2022

1]Department of Astrophysics/IMAPP, Radboud University, 6525 AJ Nijmegen, The
Netherlands

2]Department of Physics, University of Warwick, Coventry, CV4 7AL, UK

3]Cosmic Dawn Center (DAWN), Denmark

4]Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200,
Copenhagen N, Denmark

5]DTU Space, Technical University of Denmark, Elektrovej 327, 2800, Kongens
Lyngby, Denmark

6]Institute for Gravitational Wave Astronomy and School of Physics and
Astronomy, University of Birmingham, B15 2TT, UK

7]Center for Interdisciplinary Exploration and Research in Astrophysics and
Department of Physics and Astronomy, Northwestern University, 2145 Sheridan
Road, Evanston, 60208-3112, IL, USA

8]Astrophysics Research Institute, Liverpool John Moores University, Liverpool
Science Park, 146 Brownlow Hill, Liverpool, UK, L3 5RF

9]Center for Computational Astrophysics, Flatiron Institute, 162 W. 5th
Avenue, New York, 10011, NY, USA

10]Department of Physics and Columbia Astrophysics Laboratory, Columbia
University, New York, 10027, NY, USA

11]Department of Physics, The Oskar Klein Center, Stockholm University,
AlbaNova Stockholm, Sweden

12]SRON, Netherlands Institute for Space Research, Niels Bohrweg 4, NL-2333
CA, Leiden, the Netherlands

13]Australian Astronomical Optics, Macquarie University, 105 Delhi Road, North
Ryde, NSW 2113, Australia

14]Astronomy, Astrophysics and Astrophotonics Research Centre, Macquarie
University, Sydney, NSW 2109, Australia

15]Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía
s/n, 18008, Granada, Spain

16]Space Telescope Science Institute, 3700 San Martin Drive Baltimore, 21218,
MD, USA

17]Université Côte D’Azur, Observatoire de la Côte D’Azur, CNRS, Artemis,
Nice, F-063004, France

18]DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200
Copenhagen, Denmark

19]Centre for Astrophysics and Cosmology, Science Institute, University of
Iceland, Dunhagi 5, Reykjavík, 107, Iceland

20]School of Physics and Astronomy, University of Leicester, LE1 7RH,
University Road, Leicester, UK

21]Monash Centre for Astrophysics, School of Physics and Astronomy , Monash
University, 3800, Clayton, VIC, Australia

22]OzGrav, ARC Centre of Excellence for Gravitational Wave Discovery,
Hawthorn, Australia

23]School of Physics and Astronomy, University of Leicester, University Road,
Leicester LE1 7RH, UK; Jodrell Bank Centre for Astrophysics

24]INAF, Astronomical Observatory of Brera, via E. Bianchi 46, 23807, Merate
(LC), Italy

25]Department of Astronomy, The Oskar Klein Center, Stockholm University,
AlbaNova, Stockholm, Sweden

# A long-duration gamma-ray burst of dynamical origin from the nucleus of an
ancient galaxy

Andrew J. Levan<EMAIL_ADDRESS>Daniele B. Malesani  Benjamin P. Gompertz
Anya E. Nugent  Matt Nicholl  Samantha R. Oates  Daniel A. Perley  Jillian
Rastinejad  Brian D. Metzger  Steve Schulze  Elizabeth R. Stanway  Anne
Inkenhaag  Tayyaba Zafar  J. Feliciano Agüí Fernández  Ashley A. Chrimes
Kornpob Bhirombhakdi  Antonio de Ugarte Postigo  Wen-fai Fong  Andrew S.
Fruchter  Giacomo Fragione  Johan P. U. Fynbo  Nicola Gaspari  Kasper E.
Heintz  Jens Hjorth  Pall Jakobsson  Peter G. Jonker  Gavin P. Lamb  Ilya
Mandel  Soheb Mandhai  Maria E. Ravasio  Jesper Sollerman  Nial R. Tanvir  [
[  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [  [

###### Abstract

The majority of long duration ($>2$ s) gamma-ray bursts (GRBs) are believed to
arise from the collapse of massive stars Hjorth+03 , with a small proportion
created from the merger of compact objects rastinejad22 ; troja22 ; yang22 .
Most of these systems are likely formed via standard stellar evolution
pathways. However, it has long been thought that a fraction of GRBs may
instead be an outcome of dynamical interactions in dense environments
grindlay06 ; fragione19 ; mckernan20 , channels which could also contribute
significantly to the samples of compact object mergers detected as
gravitational wave sources oleary16 . Here we report the case of GRB 191019A,
a long GRB ($T_{90}=64.4\pm 4.5$ s) which we pinpoint close ($\lessapprox 100$
pc projected) to the nucleus of an ancient ($>1$ Gyr old) host galaxy at
$z=0.248$. The lack of evidence for star formation and deep limits on any
supernova emission make a massive star origin difficult to reconcile with
observations, while the timescales of the emission rule out a direct
interaction with the supermassive black hole in the nucleus of the galaxy, We
suggest that the most likely route for progenitor formation is via dynamical
interactions in the dense nucleus of the host, consistent with the centres of
such galaxies exhibiting interaction rates up to two orders of magnitude
larger than typical field galaxies stone16 . The burst properties could
naturally be explained via compact object mergers involving white dwarfs (WD),
neutron stars (NS) or black holes (BH). These may form dynamically in dense
stellar clusters, or originate in a gaseous disc around the supermassive black
hole perna21 ; lazzati22 . Future electromagnetic and gravitational-wave
observations in tandem thus offer a route to probe the dynamical fraction and
the details of dynamical interactions in galactic nuclei and other high
density stellar systems.

The evolution of most stars in the Universe is dominated by their stellar or
binary evolution. However, for a small fraction in dense environments
additional many-body interactions create new channels to the formation of
exotic stellar systems, such as the progenitors of gamma-ray bursts. These
bursts arise in at least two varieties. The first is formed from the collapse
of massive stars and typically with duration $>$ 2s Galama+98 . The second
arises from the mergers of compact objects, and typically have duration $<$2s
Abbott+17a , although recent evidence demonstrates some can be much longer
rastinejad22 ; troja22 ; yang22 .

GRB 191019A was detected by the Neil Gehrels Swift Observatory (hereafter
Swift) at 15:12:33 UT on 19 October 2019 simpson19 . The burst is
characterised by a fast rise and slower decay with additional variability
superimposed (Figure 1). The duration is measured to be $T_{90}=64.4\pm 4.5$ s
krimm19 , hence classified as a long GRB. The burst is relatively soft with a
power law photon index of $\Gamma=2.25\pm 0.05$. Its fluence is $S=(1.00\pm
0.03)\times 10^{-7}$ erg cm-2 (15–150 keV) krimm19 .

Space-craft constraints prevented a prompt slew from Swift, and observations
with the X-ray Telescope (XRT) and the Ultraviolet and Optical Telescope
(UVOT) began 52 minutes after the burst. These revealed an X-ray and UV
afterglow evans19 . We obtained optical observations of the field with the
Nordic Optical Telescope (NOT) beginning 4.52 hours after the burst perley19 .
Comparison with later epochs reveals a faint afterglow positionally consistent
with the nucleus of the host galaxy visible in each of the $g,r,i$ and
$z$-bands (Figure 2). Spectroscopy obtained with the NOT on 19 October 2019,
and confirmed with the Gemini-South telescope on 1 December 2019, found a
redshift of $z=0.248$ based on several absorption lines, including Ca H&K and
the hydrogen Balmer series (Figure 3). The standard star-forming emission
lines are notably absent from these spectra, suggesting an old galaxy.

Following these observations, we obtained deep imaging in the $g$, $r$ and
$z$-bands from the NOT and the Gemini-South telescope from 2 to 73 days after
the burst, and optical imaging with the Hubble Space Telescope at 30 and 184
days. None of these images reveal any evidence for transient emission to
limits of typically $g>24$, $r>23.5$, $z>22$ (see Figure 4).

The non-detection of optical light between 2 and 70 days places stringent
limits on any associated supernova to levels $\sim 20$ times fainter than SN
1998bw (Figure 4; see also Methods). In fact, the deepest $r$-band/F606W
limits reach absolute magnitudes of $M\sim-16$. This is comparable to the
faint end of the core-collapse supernova distribution and fainter than any
known stripped-envelope events found in the large sample from the Zwicky
Transient Factory perley20 . It is also fainter than optically selected tidal
disruption events nicholl22 ; hammerstein22 . The limiting luminosity is
comparable to the peak luminosity of kilonovae. However, our observations
probe much longer timescales than those of kilonovae, such that we could not
rule out events equivalent to AT2017gfo villar+17 . The lack of a SN detection
cannot readily be ascribed to dust extinction since the spectral energy
distribution of the afterglow constrains this to be small (see Methods).

Combining HST UV observations with our spectroscopy and archival imaging, we
fit the available photometric and spectroscopic data with the stellar
population inference code Prospector (Figure 3 and see Methods). The results
favour an old stellar population for the host, with the majority of stellar
mass forming $>1$ Gyr ago, and little ongoing star formation ($\approx
0.05~{}M_{\odot}$ yr-1). The stellar mass itself is found to be $\approx
3\times 10^{10}~{}M_{\odot}$.

The location of GRB 191019A in the galaxy nucleus could indicate an origin
associated with the supermassive black hole which resides there, with scaling
relations implying a black hole with a mass of a $\text{few}\times 10^{7}$
$M_{\odot}$ kormendy13 . However, the timescales for the emission are too
short for either variability in an active galactic nucleus (AGN) or a tidal
disruption event (TDE) (see Methods). Instead, the burst most likely arises
from a stellar progenitor. The lack of a supernova and the location in an old
population rule out a massive star. Instead, it appears that GRB 191019A
belongs to the population of apparently long GRBs formed from compact object
mergers rastinejad22 ; troja22 ; yang22 . Its apparent energy release and
afterglow luminosity are consistent with this group of GRBs (Methods).

However, the nuclear location of the GRB on its host galaxy differs from
compact object merger expectations. Systems formed via standard stellar
evolution channels involve two supernovae; at each supernova, the combination
of natal kicks and those induced from mass loss combined to give the binary a
substantial (50–500 km s-1) systemic velocity. Indeed, no short GRB with sub-
arcsecond localisation is consistent with the nucleus of its host galaxy
fong22 .

We suggest instead that the binary which created GRB 191019A formed via
dynamical interactions in the dense nucleus of its host galaxy. Dynamical
channels for compact object formation may be due to many-body interactions in
dense stellar systems such as globular clusters grindlay06 ; ye20  or nuclear
star clusters in galaxies antonini16 ; fragione19 . Alternatively, they may
also form at a significantly enhanced rate in the gaseous discs that surround
supermassive black holes mckernan20 ; tagawa20 .

The host galaxy of GRB 191019A appears similar to those that preferentially
host tidal disruption events, with a very compact core and Balmer absorption
lines. The Lick indices for H$\delta$ in absorption and H$\alpha$ in emission
are $1.54^{+1.44}_{-0.74}$ and $2.51^{+1.81}_{-2.51}$, consistent with those
of the TDE population which make up only $\sim 2$% of SDSS galaxies, but 75%
of the TDE hosts French17 . The TDE rate effectively measures the stellar
interaction rate close to the black hole. Scattering events are responsible
for placing stars on paths which cross closer than the tidal radius for the
star around the SMBH. The preference for TDEs in galaxies of certain types is
related directly to their dense stellar environments, and interaction rates
stone16 . At face value, then, the host galaxy of GRB 191019A may have a
dynamical interaction rate one to two orders of magnitude larger than typical
galaxies.

If GRB 191019A results from a dynamically formed compact object merger, it may
arise from several possible merger products, including NS-NS, NS-BH, NS-WD and
BH-WD. The nature of the merger product and its location (e.g. stellar cluster
versus gas disc) should have a direct impact on the observed properties of the
burst, particularly concerning duration, spectral hardness and energetics.

In the case of NS-NS or NS-BH systems, one may wonder why no apparent short
($<2$ s) spike is observed in the prompt lightcurve, as in short GRBs with
extended emission. The detection of the kilonova in GRB 211211A demonstrates
that such a short spike is not necessarily required, although GRB 211211A
appears to show other similarities to extended emission (EE) bursts gompertz22
. However, GRB 191019A may arise from a similar population where the contrast
between “spike” and “extended” emission is smaller perley09 , or that the
extended emission is beamed with a larger opening angle than the initial spike
and is unseen in this case Bucciantini12 ; lu22 . Alternatively, mergers
involving white dwarfs have longer timescales naturally king07 , and such an
event is also possible here. Indeed, interactions in dense clusters tend to
leave the more massive components in binaries, so BH-NS or BH-WD mergers may
be favoured ye20 . White dwarf-containing systems should yield rapid,
relatively faint transients, with one event, AT2018kzr mcbrien19 ;
Gillanders20 , suggested to arise from the merger of a white dwarf with a
black hole. Our observations are not sufficiently sensitive to constrain the
presence of such a signal in GRB 191019A.

Alternatively, the nuclear location also allows compact object mergers within
a disc around the supermassive black hole, although there is no strong
evidence for AGN activity in the host (see Methods). In these discs, the
compact object binaries are frequently formed by “gas capture” mergers, which
can substantially enhance the rate, despite the relatively small number of
stars within the disc tagawa20 . In this scenario, the long duration may well
be expected, even for an intrinsically short engine. The higher densities
within the disc cause the external shock to form and slow much closer to the
progenitor than in bursts with a normal interstellar medium density. This
extra baryon loading may effectively choke the jet perna21  for very high
densities. However, this interaction’s effect smears out the prompt emission
over an extended period. A very recent and explicit prediction of compact
object mergers within discs is that intrinsically short-hard GRBs should
become longer and softer lazzati22 , with a notable hard-soft evolution. This
is exactly what is seen in GRB 191019A.

It is relevant to consider whether similar events exist within the GRB
population but have been hitherto unrecognised. The vast majority of long GRB
hosts are star-forming galaxies and, where searches are possible, usually show
the signatures of broad-lined type Ic supernovae. There is a small population
of long bursts without supernova signatures Fynbo+06 ; GalYam+06 . Some of
these have already been classified as short GRBs with extended emission
(Gehrels+06, ), however there are additional bursts which bear further
scrutiny. GRB 111005A Michalowski+18  was localised only via its radio
afterglow but has deep limits on associated supernova emission. It lies in a
local galaxy at only 55 Mpc and is also close to the nucleus. It could well
have arisen from a compact object merger as suggested by le22  and its
location raises the prospect of dynamical formation. GRB 050219A does not have
a sub-arcsecond localisation, but is likely associated with a post-starburst
galaxy whose properties are similar to the host of GRB 191019A rossi14 .
Finally, there are several long GRBs whose locations are consistent with their
host nucleus fruchter06 , although most of these are in star-forming hosts and
likely arise from massive star collapse. Overall, the observational evidence
suggests that, at most, a few per cent of the observed (long and short) GRB
population forms via dynamical channels and that most of the observed systems
arise via stellar (binary) evolution.

Identifying a likely dynamically produced GRB offers some of the first
evidence for forming stellar-mass compact objects via dynamical channels in
galactic nuclei. The mergers of such systems have received significant
attention as a possible explanation for a fraction of the observed
gravitational-wave population, particularly with regard to more massive black
holes which can be formed via successive mergers fragione22 . The gamma-ray
bright population of mergers may be dwarfed by those that do not emit such
high-energy flashes. In particular, very high densities within gaseous discs
can result in the choking of any GRB-like emission perna21 , and BH-BH mergers
are generally expected to be EM-dark. GRBs in dense galactic nuclei therefore
offer a unique new route to probe exotic compact object formation channels.

Figure 1: a) The $\gamma$-ray light curve of GRB 191019A as observed by the
Swift-BAT. The burst consists of a single emission episode, with additional
intrinsic variability. The burst begins with a short spike, but it is not
especially hard, nor separated from the bulk of the emission. The lower panel
shows the hardness ratio between the 50–100 and 15–25 keV bands, demonstrating
some degree of spectral softening, with the initial peak being the hardest
emission episode. b) The location of GRB 191019A on the hardness–duration
plane. The background red points represent bursts from the Swift-BAT catalog
Lien+16 , while GRB 191019A is indicated with the dark blue circle. Also
marked are the locations of bursts identified as short+EE based on the
duration of their initial complex and extended emission (EE) separately. The
properties of GRB 191019A are comparable with the properties of the EE-
component in other bursts.

Figure 2: Optical images of the afterglow of GRB 191019A and its host galaxy.
a) The $i$-band afterglow discovery image from the NOT. b) The result of a
PSF-matched image subtraction with an image taken on 29 October. A residual is
clearly visible at the centre of the galaxy. c) The field as observed by HST
in April 2020, matched to the NOT images. d) A zoomed in region around the
host galaxy of GRB 191019A as seen with HST (as indicated with the cyan box in
panel c). The ellipses indicate the $2\sigma$ uncertainty regions for the
optical afterglow on the host as inferred from the NOT $g$ (cyan), $r$
(green), $i$ (yellow) and $z$ (magenta). The location of the afterglow is
consistent with the nucleus of the host galaxy with a projected offset, based
on the $i$-band measurement, of $r_{\text{proj}}=78\pm 109$ pc.

Figure 3:  The optical spectrum of the host galaxy of GRB 191019A as observed
with the NOT. The spectrum shows no emission lines associated with star
formation (the expected locations of strong emission lines are marked with
grey bands, and telluric absorption in pink). There is weak evidence for
emission from [N ii] (6584 Å). The locations of prominent absorption features
from which the redshift is determined are marked with dashed lines. Also shown
are the results of a Prospector fit to the stellar spectrum (e.g. omitting any
emission lines). Any lines would appear in the residuals.

Figure 4: Comparison between the upper-limits obtained from our targeted
observations of GRB 191019A and the expectations of the lightcurve from
supernova or tidal disruption events. The upper limits represent the depth of
our NOT, Gemini and HST observations, while the solid lines correspond to the
expectations of SN 1998bw at $z=0.248$, based on the light curves of
clocchiatti11 . The right hand panel shows histograms of the peak absolute
magnitude distributions of supernovae and tidal disruption events found by ZTF
perley20 ; hammerstein22 . Also shown are the faintest and fastest evolving
tidal disruption event iPTF16fnl blagorodnova17 ; nicholl22 , AT2018kzr,
suggested to form via a BH-WD mergers mcbrien19  and AT2017gfo, associated
with GW170817 villar+17 . Our optical observations reach a depth where we
would have expected to observe the vast majority of supernovae or tidal
disruption events. However, we do not have sensitivity to detect kilonovae
like AT2017gfo.

## Methods

###  Swift Observations

#### BAT

BAT data were downloaded from the UK _Swift_ Science Data Centre (UKSSDC;
Evans07 ; Evans09 ). Reduction was performed using the dedicated pipeline
batgrbproduct v2.48 from the High Energy Astrophysics Software package
(HEAsoft v6.28; HEAsoft )111http://heasarc.gsfc.nasa.gov/ftools. We extract
count-rate light curves in four energy bands: 15–25 keV, 25–50 keV, 50–100 keV
and 100–150 keV, using the batbinevt routine with 64 ms time bins. Spectral
lag in the $T_{90}$ interval is calculated with the Python routine
signal.correlate from the scipy package SciPy . The time lag is taken to be
the value corresponding to the peak of the correlation coefficient, and the
confidence interval as $2/\sqrt{n-d}$, where $n$ is the size of the data array
and $d$ is the measured lag Tonry79 .

To obtain the hardness ratios presented in Figure 1, BAT spectra in the energy
range 15–150 keV were extracted with batbinevt. Spectra were produced for the
duration of the initial pulse complex (IPC; see Figure 1), and from the end of
the IPC to $T_{90}$ (marked ‘EE’ in Figure 1), following the definitions of
these epochs in Barthelmy05 ; Gehrels+06 ; perley09  for GRBs 080503, 060614
and 050724, respectively. Spectra were then fit in xspec v12.11.1 with an
absorbed power-law model of the form cflux*tbabs*ztbabs*pow Wilms00 , where
cflux is used to measure the time-averaged flux in the 25–50 keV and 50–100
keV bands in each spectrum. Absorption in the Milky Way is fixed to the values
derived in Willingale13 , while flux, photon index and redshifted absorption
are free parameters.

#### XRT

XRT data for light curves and spectral parameters are taken directly from the
UKSSDC Evans07 ; Evans09 .

#### UVOT

The Swift/UVOT began settled observations of the field of GRB 191019A 3294 s
after the Swift/BAT trigger. The source counts were extracted initially using
a source region of $5^{\prime\prime}$ radius. When the count rate dropped to
below 0.5 counts per second, we used a source region of $3^{\prime\prime}$
radius. In order to be consistent with the UVOT calibration, these count rates
were then corrected to $5^{\prime\prime}$ using the curve of growth contained
in the calibration files. Background counts were extracted using 3 circular
regions of radius $15^{\prime\prime}$ located in source-free regions. The
count rates were obtained from the image lists using the Swift tools uvotevtlc
and uvotsource, respectively. At late times the light curves are contaminated
by the underlying host galaxy. In order to estimate the level of
contamination, for each filter we combined the late time exposures (beyond
$10^{7}$ s) until the end of observations. We extracted the count rate in the
late combined exposures using the same $3^{\prime\prime}$ and
$5^{\prime\prime}$ radii apertures, aperture correcting where appropriate.
These were subtracted from the source count rates derived with the same size
aperture to obtain the afterglow count rates. The afterglow count rates were
converted to magnitudes using the UVOT photometric zero points (Poole et al.
2008; Breeveld et al. 2011). To improve the signal-to-noise ratio, the count
rates in each filter were binned using $\Delta t/t=0.2$.

### Nordic Optical Telescope

We obtained multiple epochs of observation of GRB 191019A with the Nordic
Optical Telescope (NOT) and ALFOSC imaging spectrograph. Our first night
observations were obtained in the $griz$ bands, beginning 0.19 days after the
burst. Images were reduced using standard procedures. To search for transient
emission we undertook PSF matched image subtraction alard98 . This revealed a
clear transient source in the first epoch in all four bands. Further
observations were obtained at 2.4, 3.2, 10.2, 34 and 245 days. However, these
observations did not reveal any transient emission. A full log of imaging
observations is shown in Table 1.

In addition to imaging observations we also obtained a spectrum of GRB 191019A
on 19 October 2019, approximately 6 hours after the GRB. The spectrum was
processed through IRAF for flat-fielding, wavelength and flux calibration.

### Gemini South

We obtained a series of observations of the location of GRB 191019A from the
Gemini-South Observatory using GMOS. Imaging observations were obtained in the
$g$, $r$ and $z$-bands at 8 epochs between 11 and 70 days after the burst,
with the primary aim of detecting and characterising any associated supernova.
Data were bias subtracted, flat-field corrected and combined via the Gemini
IRAF package. To determine any transient contribution we use two different
approaches. The first is the standard approach of image subtractions which we
attempted via the HOTPANTS code. These images reveal no evidence for transient
emission. However, because of the compact nature of the host galaxy core which
is unresolved in ground based resolution, not all epochs yielded clean
subtractions. Therefore, to determine limits across all epochs we utilise the
simpler approach of direct photometry in a large (3 arcsecond) apertures.
There is no evidence for any variation in the galaxy with the RMS between the
different epochs corresponding to 1.3% in $g$, 1.0% in $r$ and 1.5% in $z$.
This suggests that there is no variation in the source across the 11–70 day
period of observations. To obtain limits for individual epochs we set the host
galaxy value as the mean of all epochs and subtract this from each individual
epoch to obtain measured fluxes at the time of each observation. These values
are tabulated in Table 1 and are plotted as $3\sigma$ upper limits in Figure
4. Photometric calibration is performed against Pan-STARRS.

###  Hubble Space Telescope Observations

We observed GRB 191019A with the Hubble Space Telescope (HST) at two epochs on
19 November 2019 and 24 April 2020. At each epoch we obtained imaging
observations in the F606W (exposure times of 180 and 680 s, respectively)
filter and grism spectroscopy with G800L. We reduced the imaging with the
astrodrizzle software, and subtracted the first epoch from the second. Such an
analysis is complicated because in the first epoch the first image was short
(180 s) and intended to act as a direct image for the grism spectroscopy.
Subsequently multiple cosmic rays are present that cannot be removed by the
addition of multiple images. This complicates direct photometry of the galaxy.
However, subtraction of the two epochs of imaging reveals no evidence for any
transient emission at the burst location. Inserting artificial stars suggests
these would be readily visible should they be brighter than
$\text{F606W}>23.5$ AB.

In addition to these observations we also obtained UV observations in F225W
and F275W with exposure times of 2200 s. The data were reduced via
astrodrizzle and aligned to our NOT and Gemini observations. The host galaxy
is well detected in both filters, and appears extended. The resulting
photometry is shown in Table 3.

### Astrometry

To determine the location of GRB 191019A on its host galaxy we performed
astrometry between the images taken with the NOT on 19 October 2019 and that
with HST on 24 April 2020. We chose 20 compact sources in common to each image
and derived a map between the two sets of pixel co-ordinates via the IRAF task
geomap in each of the $g$,$r$,$i$ and $z$-bands. The resulting uncertainties
arise from the astrometric fit and the uncertainty in the centroid of the
afterglow in the NOT subtracted images. We estimate the centroid error be 0.3
ACS pixels (appropriate for a S/N=30 detection of the source with a seeing of
$\sim 1.0$ arcseconds). This is typically (but not always) smaller than the
error from the astrometric fit. The resulting positions are shown in Figure 2.
In the $i-$band (which has the tightest astrometric fit) we find that the
offset from the centroid of the host galaxy is $\delta_{x(i)}=0.30\pm 0.41$
and $\delta_{y(i)}=0.27\pm 0.41$ pixels. In $g$, $r$ and $z$ the corresponding
values are $\delta_{x(g)}=0.44\pm 0.82$, $\delta_{y(g)}=0.03\pm 1.21$,
$\delta_{x(r)}=0.43\pm 0.50$, $\delta_{y(r)}=1.48\pm 0.54$,
$\delta_{x(z)}=0.85\pm 0.91$. $\delta_{y(z)}=-0.68\pm 0.87$. We therefore
conclude that the source is consistent with the nucleus of the host galaxy at
a projected offset (based on the $i-$band astrometry) of $r=0.020\pm 0.029$
arcseconds or $78\pm 109$ pc at $z=0.248$.

### Chance alignment

It is relevant to consider the probability of chance alignment of a given
position with a galaxy. Such chance alignments are inevitable in large samples
of transient sources, such as the Swift-BAT catalog. However, the location of
GRB 191019A, so close to the nucleus of a relatively bright ($r\sim 19$)
galaxy, leads to an extremely small chance probability. Formally, following
Bloom+02 , the probability of lying within $0.04^{\prime\prime}$ of such a
host galaxy is $\sim 10^{-6}$. Therefore, even considering the $\sim 1000$
long GRBs observed by Swift, the likelihood of a chance alignment of GRB
191019A with the nucleus of this galaxy is very small. We therefore consider
the association to be robust.

### Afterglow properties

#### Light curve

The optical afterglow is detected only at a single epoch at $\sim 0.2$ days.
All observations beyond this point are upper limits.

The X-ray light curve parameters, obtained from the UKSSDC, show that the
X-ray afterglow can be adequately modelled by a single power-law with index
$\alpha_{1}=1.27^{+0.17}_{-0.15}$. Alternatively, a broken power-law with
$\alpha_{1}=-0.14^{+0.54}_{-0.16}$, $\alpha_{2}=1.6^{+0.5}_{-0.4}$ and a break
time of $t_{b}=(5.9^{+4.2}_{-1.8})\times 10^{3}$ s also provides a good fit,
although not statistically required (chance improvement probability of 4.5%,
or $\sim 2\sigma$).

To place the X-ray (and early $\gamma$-ray data) in context with the overall
Swift population, we retrieve from the Swift Burst Analyser Evans+09  the
$\gamma$-ray and X-ray light curves of all Swift GRBs detected up until 9
October 2022. We select all GRBs with at least 2 detections by BAT and XRT
each and a measured redshift with an accuracy of $\leq 0.1$ in redshift space.
To divide the final input sample of 395 GRBs into long and short GRBs, we
follow fong22 . In total, our sample consists of 356 long and 39 short GRBs.
We processed their light curve data and moved them to their rest-frames
following Schulze+14 . Figure 5 shows the parameter space occupied by the long
(left) and short (right) GRBs as a density plot and the BAT+XRT light curve of
191019A in blue. In both plots, we also display the light curves of GRB
050219A and 211211A (in red) and, in the right hand panel, also highlight the
short GRBs with extended emission Gompertz+20 .

The X-ray light curve of GRB 191019A is relatively poorly sampled, but its
evolution in luminosity space is consistent with the population of short-GRBs
with extended emission (see Figure 5), while being far less consistent with
the long-GRB population. This offers further support of the interpretation of
GRB 191019A as belonging to the population of GRBs created via compact object
mergers.

Figure 5: The X-ray afterglow of GRB 191019A in context with other GRBs. The
left hand panel shows a comparison to the long duration GRBs, and the right
hand panel to the short bursts. The greyscale background indicates the
fraction of bursts at a given luminosity. GRB 191019A lies at the fainter end
of the prompt emission for long GRBs (i.e. within the first hundred seconds),
and has an X-ray afterglow which is significantly underluminous for long
bursts. However, it has a luminosity entirely consistent with short GRBs.

#### Spectral energy distribution and extinction

A straightforward way to explain the non-detection of any supernova emission
would be to invoke dust extinction. To explain the non-detection of the
supernova in our observations would require $A_{V}>3$ mag. However, the
afterglow in this case would also be subject to extinction and would be red.
The detection in the UVW2 ultraviolet filter offers a strong indication that
the extinction is low.

Moreover, corrected for the (small) Galactic extinction, the optical and UV
data do not show a reddened spectrum (Fig. 6), and the spectral energy
distribution is well described with a power-law with spectral index
$\beta_{\rm opt}=0.78\pm 0.08$, which is consistent both with the X-ray value
$\beta_{\rm X}=1.0^{+0.4}_{-0.3}$ and especially with the optical-to-X-ray
slope $\beta_{\rm OX}=0.82$ DAi19 . This indicates that the optical flux is
not suppressed, indicating negligible extinction, and that a single power law
can describe the entire data set. Supporting this finding is the X-ray derived
hydrogen-equivalent column density $N_{\rm H}$ = 1.2${}^{+1.6}_{-1.2}\times
10^{21}$ cm-2, consistent with zero. All of these diagnostics argue against
any role of extinction.

Figure 6: The X-ray to optical spectral energy distribution of the GRB 191019
afterglow, 0.21 days after the detection (average time of the first-night NOT
observations). The optical data ($z$ to UVW2) are corrected for the (small)
Galactic extinction corresponding to $A_{V}=0.10$ mag. The solid butterfly
represents the observed X-ray spectrum and uncertainty (0.3–10 keV).
Optical/UV and X-ray points have been extrapolated to the same time assuming
they follow the observed X-ray decay. In practice, this is a small change for
the $griz$ NOT data, which are driving the optical fit. The yellow/orange
shaded area represents the best-fit to the optical/UV data, and its
extrapolation to the X-ray range, while the grey region shows the same
extrapolation of the X-ray to the optical/UV regime. The X-ray and UV/optical
spectral indices are consistent with each other, indicating no requirement for
any additional extinction.

### Host galaxy properties

The host galaxy is morphologically smooth and highly centrally concentrated
(Figure 8). We determine the surface brightness profile via fitting elliptical
isophotes to the late time HST observations. The peak surface brightness is
$\sim 16.5$ mag arcsec-2, almost a magnitude brighter than, for example, the
central surface brightness of the very luminous host of the short GRB 050509B
(at $z=0.22$, a similar redshift). The surface brightness profile is not well
modelled by a single Sersic profile, but constitutes a near point-like source
with lower surface brightness emission. Its 20, 50 and 80% light radii are
0.09, 0.27 and 0.75 arcsec. Notably, its concentration index $r_{20}/r_{80}$
is extreme compared to most samples of galaxies conselice03 , but comparable
to those of TDE hosts (see Figure 9). It is relevant to consider if some of
this light could arise from an AGN. However, we cannot confirm this in the
absence of any AGN-like emission lines in the optical spectrum of the source.
The presence of a weak [N ii] line is apparent in both the NOT and Gemini
spectra, and the absence of oxygen or hydrogen emission lines may favour a
more AGN-like set of line ratios, but such an interpretation is not
conclusive. A late time observation with the Swift X-ray Telescope suggests an
upper limit of $F_{\rm X}<3\times 10^{-14}$ erg s-1 cm-2, corresponding to a
luminosity of $L_{\rm X}<6\times 10^{42}$ erg s-1. This rules out X-ray
luminous AGN, but not fainter, low luminosity examples. Finally, the colours
in the WISE catalog of $\text{W1}-\text{W2}=0.25\pm 0.12$ lie far from the
expected colours of AGN in these bands ($\text{W1}-\text{W2}>0.8$).

Figure 7: The star (left) and mass (right) formation histories of the host of
GRB 191019A, determined through the Prospector fitting. The dark green lines
indicate the median SFR and mass formed in each bin, and the light green
regions represent the $1\sigma$ uncertainty. We find that the majority of
stars and mass in the galaxy formed at $t_{\textrm{lookback}}>1$ Gyr, and that
the host has transitioned into a quiescent galaxy, with a low present-day SFR.

We fit the optical NOT/ALFOSC spectrum and broader-band photometry of the host
galaxy with Prospector (Leja+17, ; jlc+2021, ), a stellar population modeling
inference code, to determine its stellar population properties, such as
stellar population age, mass formation history, and star formation history
(SFH). Prospector samples each property parameter space with a nested sampling
fitting routine, dynesty (Dynesty, ), and produces model spectral energy
distributions with FSPS and Python-fsps (FSPS_2009, ; FSPS_2010, ). We apply a
Milky Way extinction law (MilkyWay, ), Chabrier IMF (Chabrier2003, ), and a
non-parametric SFH to the fit. We choose a non-parametric SFH model as we can
then more accurately determine when the majority of stars formed in the
galaxy’s history, and thus when the progenitor likely formed. However, we note
that most stellar population modeling to date uses a parametric SFH that tends
to result in lower stellar masses and stellar population ages. We use a non-
parametric SFH with seven age bins; the first two are between 0 and 30 Myr and
30 and 100 Myr, and the final five are log-spaced from 100 Myr to the age of
the universe at GRB 191019A’s redshift ($z=0.248$, $t_{\textrm{univ}}\sim
10.78$ Gyr). We further apply a mass-metallicity relation (gcb+05, ) to sample
realistic masses and stellar metallicities, and a dust 2:1 ratio between the
old and young stellar populations (pkb+14, ; Leja2019, ; cab+20, ). We fit the
model spectral continuum with a 10th order Chebyshev polynomial and include a
nebular emission model with gas-phase metallicity and a gas-ionization
parameter in the fit to measure spectral line strengths. Since the host may
also contain an AGN we also add two AGN components, that dictate the mid-IR
optical depth and the fraction of AGN luminosity in the galaxy.

We find that the host of GRB 191019A has a stellar population age of
$4.34^{+0.88}_{-0.47}$ Gyr (median and $1\sigma$), stellar mass with
$\log(M/M_{\odot})=10.57^{+0.02}_{-0.01}$, and current-day SFR of
$0.06^{+0.08}_{-0.03}~{}M_{\odot}$ yr-1, thus is currently a quiescent galaxy,
given the sSFR and redshift. From a limit of the H$\alpha$ flux, we determine
an H$\alpha$ $\text{SFR}<0.12^{+0.07}_{-0.06}~{}M_{\odot}$ yr-1. We report the
SFH and mass formation history of the host in terms of the lookback time
($t_{\textrm{lookback}}$), and show the subsequent histories in Figure 7. We
find that the majority of stellar mass and stars formed at
$t_{\textrm{lookback}}\gtrsim 1$ Gyr, with a steep decline in mass and star
formation to present-day, $\sim 99$% of the stellar mass was assembled $>1$
Gyr before the merger (Figure 7, right). Thus, the progenitor of GRB 191019A
has a higher a priori probability of forming $>1$ Gyr ago, making it unlikely
to originate from a young stellar progenitor.

As an independent check of the absence of emission lines in the host galaxy of
GRB 191019A we also fit the NOT spectrum with penalised pixel fitting pPXF
Cappellari2022 , where we fit only the stellar component and no emission lines
following inkenhaag22 . As with our Prospector fitting the resulting residuals
provide no evidence for emission features.

#### Comparison with short and long GRB host galaxies

We can compare the properties of the host of GRB 191019A with those of other
long and short duration GRBs. A bulk comparison is often done utilizing the
stellar mass and star formation rate of these galaxies. This is plotted for a
sample of long Perley2013  and short nugent22  host galaxies in Figure 10. The
long GRBs overwhelmingly favour actively star forming hosts, with high
specific star formation rates. In contrast the short GRBs span a wide range of
star formation rates including a modest fraction apparently in quiescent
systems.

There are two long GRB host galaxies which stand out from the apparent trend.
One is the host of GRB 191019A. The other is the host of GRB 050219A rossi14 .
This burst is only localised via its X-ray afterglow, but has a comparable
redshift to GRB 191019A and similar energetics ($E_{\rm iso}\sim 10^{51}$
erg). With only an X-ray position it is not possible to accurately determine
if the burst is nuclear, and indeed the probability of chance alignment is
larger due to the poor localisation ($P_{\text{chance}}\sim 0.8\%$). However,
it also lies in a galaxy showing Balmer absorption lines but little evidence
for star formation. Rossi et al. rossi14  also classify it as a post starburst
system. The similarities with GRB 191019A are striking, and we consider it a
possible example of a similar event.

Figure 8: The surface brightness profile of the GRB 191019A host as determined
via elliptical isophote fitting in ellipse. The host has a very compact,
almost point-like core, although its surface brightness profile is not well
fit with either a point-source plus a Sersic profile, nor the sum of two
Sersic profiles, especially beyond $1^{\prime\prime}$.

Figure 9: Concentration and asymmetry measurements for the host of GRB 191019A
compared with those of a sample of normal galaxies from conselice03 , and the
hosts of tidal disruption events from french20 . Morphologically, the GRB
191019A host appears very similar to the TDE systems, consistent with an
origin in dense environments where stellar interactions are common.

Figure 10: A comparison of the host properties (stellar mass and specific star
formation rate) of GRB 191019A with those of long GRBs (from Perley2013 ) and
short duration GRBs (from nugent22 ). The GRB 191019A host has a very low star
formation rate, and lies in a region devoid of other long GRB hosts. However,
this region is populated by short-GRB host galaxies. The same is true for the
host of GRB 050219A rossi14 . Another plausibly similar event, GRB 110005A
Michalowski+18  is in a region populated by both long and short GRB hosts.

### GRB 191019A as a merger-GRB

#### Collapsars

At first sight, GRB 191019A appears a relatively normal, if soft, long
duration GRB. It consists of a fast rise with a slower decay with some
variability super-imposed on this decay. It is not a short GRB, nor is it
obviously a member of the population of short GRBs with extended emission,
where an initial spike is followed by longer-lived, softer emission. However,
the location in an old host galaxy and the lack of any visible supernova
emission strongly disfavour the presence of any massive stars which could
produce collapsar-like events. Although previously identified supernova-less
GRBs have been suggested to arise from direct collapse of massive stars to
black holes Fynbo+06 ; GalYam+06 ; DellaValle+06 , in those cases the bursts
were associated with star forming host galaxies, and in one case with a highly
active star forming region within them Fynbo+06 . In principle massive stars
can be built by the merger of lower mass stars in dense environments pg04 .
However, with a $>1$ Gyr old population, the turn off mass is $<2$
$M_{\odot}$. It would take multiple mergers to build a star sufficiently
massive to directly collapse to a black hole.

#### Tidal disruption events

The location in the galaxy nucleus could be indicative of an origin associated
with the supermassive black hole which resides there. In particular, a
population of relativistic tidal disruption events have been identified by the
Swift-BAT bloom11 ; burrows11 ; levan11 ; cenko12 ; brown15 . However, these
events are typically of very long duration and were visible to the Swift-BAT
for several days at a luminosity of $>10^{47}$ erg s-1. Alternatively, more
typical tidal disruption events do not generate detectable $\gamma$-ray
emission but are found with long-lived ($>10^{7}$ s), lower luminosity X-ray
emission ($\sim 10^{42}$–$10^{44}$ erg s-1 auchettl17 ; saxton20 ), as well as
long-lived optical/UV thermal signatures significantly brighter than our
limits for GRB 191019A (Figure 4) perley20 .

The timescale for tidal disruption events is generally thought to be related
to the return time for the most bound ejecta of the disrupted star. It can be
much shorter in the case of white dwarfs disrupted by intermediate mass black
holes maguire20 . Such a black hole mass is inconsistent with that inferred
for the black hole mass in the GRB 191019A host via scaling relations (few
$\times 10^{7}$ $M_{\odot}$). Furthermore, even these systems have generally
been discussed in the context of long GRBs with extremely long durations
(levan14, ; macleod14, ), and simulations suggest they should give rise to
detectable X-ray and optical emission for tens of days following the
disruption macleod16 . There is also a suggested population of micro-TDEs, in
which a main sequence star is disrupted by a stellar mass black hole Perets16
. However, these events are also suggested as an explanation for the longest
duration (so-called ultra-long) GRBs levan14  and do not naturally match the
timescales here.

#### Compact object mergers

The recent identification of a kilonova in GRB 211211A demonstrated that much
longer lived bursts can arise from compact object mergers rastinejad22 ;
yang22 ; troja22 . For GRB 191019A, the older host and lack of supernova would
be consistent with this expectation. However, it is relevant to consider if
its properties are consistent with previous examples of long-lived merger-
GRBs.

The $\gamma$-ray light curve of GRB 191019A does start with a short lived (0.5
s), somewhat harder pulse, but this is not clearly distinct from the overall
prompt emission. However, in the population of short GRBs with extended
emission there is a range of contrast ratios between the short spike and the
extended emission ranging from 0.2 to $>50$ perley09 . There is also a
substantial variation in the time between the short spike and the appearance
of extended emission from $\sim 0$ to $\sim 20$ s NorrisBonnell06 ; gompertz22
. The combination of a low contrast and short delay could readily mean that
some bursts are not easily identifiable as short+EE based on their light
curves. While at durations of $\sim 1$ minute the majority of GRBs are likely
to arise from collapsars, a small fraction from mergers is entirely plausible.
Indeed, the softer than usual spectrum for GRB 191019A places it in a region
of hardness duration space which is comparable to extended emission see in
other GRBs (see Figure 1).

We also measure the spectral lag between the harder and softer emission. In
collapsar GRBs there is a noticable spectral lag in which the softer emission
is delayed (lags) the harder emission. Such a measurement is not seen in
merger-GRBs Gehrels+06 . For GRB 191019A, formally the soft emission leads the
harder emission with a measured spectral lag of $\tau=-96\pm 63$ ms (between
the 50–100 and 15–25 keV bands, with 16 ms binning). This lag measurement is
atypical for long GRBs, and suggests a merger-origin is plausible.

It may also be the case that the burst arises from a merger, but there is no
short spike in this case (hidden or otherwise). This may be the case if, for
example, there are different beaming angles for the short spike and extended
emission. Indeed, it has been suggested that a population of orphan extended
emission bursts should also be present Bucciantini12 ; lu22 . Furthermore,
there are claims that a population of fast X-ray transients seen in narrow
field X-ray observations (e.g with Chandra) arise from compact object mergers
xue19 ; qv22 . None of these systems show initial short spikes (albeit in a
much softer energy band than the Swift-BAT).

Finally, mergers within the discs surrounding supermassive black holes create
jets with very different dynamics to those in a tenuous interstellar medium.
In particular, the high densities result in the formation of an external shock
very close to the progenitor, and the dissipation of energy within this shock
causes bursts which are intrinsically short and hard to be smeared out and
softened lazzati22 . Although not conclusive, the similarity of GRB 191019A to
these models is remarkable.

#### Dynamical formation channels

There are various ways in which dynamical interactions create compact object
binaries. Firstly, the interactions can create new compact object binaries via
2+1 interactions which tend to leave the more massive components within a
binary. Once formed these binaries can be further hardened (have their
separations reduced) by additional interactions and eventually merger within
the Hubble time heggie03 . The SMBH can also act as a perturbation, in
particular via the creation of Kozai-Lidov cycles, which increase the
eccentricity and decrease the periapsis separation of the binary, thus
increasing GW energy losses and ultimately enhancing the merger rate hoang18 .
Fragione et al. fragione19  find the rates of compact object binary formation
in galactic nuclei to be of order 1 Gpc-3 yr-1, although these are highly
sensitive to the details of the dynamics within the galactic nuclei. If indeed
galaxies similar to the hosts of GRB 191019A have much higher interaction
rates than MW-like galaxies, this could be enhanced significantly.

A challenge for dynamical production via many-body interactions is that these
interactions tend to leave the most massive objects within the binaries ye20 .
Hence, the expected rates of NS-NS mergers within globular clusters are much
smaller than the BH-BH rate ye20 . This is somewhat in conflict with the 1-3
out of $\sim 20$ BNS systems in the Milky Way which are found within globular
clusters (the range reflects the uncertainty in the nature of the compact
companions in some cases). It may be that in these systems the BNS is a
transitory state, and further interactions may yet take place before the GW-
induced merger. However, the rate of dynamical formation is higher than the
rate of mergers in clusters. Many NS-NS and BH-NS systems which are
dynamically formed in globular clusters are ejected, and ultimately merge far
from the cluster. The escape velocities of globular clusters are small ($\sim
50$ km s-1), in contrast, the escape velocities from the centre of the GRB
191019A host are much larger. The central regions cannot be directly resolved,
but assuming the half-light radius is also half the stellar mass the escape
velocity from $\sim 1$ kpc would be $>300$ km s-1, so that binaries ejected
via dynamical formation would also likely merge close to the nucleus,
especially since these ejected systems likely have lower velocities than field
binaries ye20 . Of course, should systems formed in the field also be formed
while the galactic potential is so centrally concentrated they are also less
likely to escape, although would be placed on eccentric orbits, spending most
of their time at larger projected radii.

In addition to these star-star (or star-SMBH) interactions there are also
interactions with the gaseous disk which may exist around the SMBH. The rates
of such systems are subject to significant uncertainty and debate; upper
limits as high as 400 Gpc-1 yr-1 mckernan20  have been suggested. Indeed,
associations with unusual AGN outbursts have been claimed for some
gravitational wave (BBH) sources at moderate significance graham20 ; graham22
.There remain significant model and observational uncertainties associated
with these results tagawa20 , however, if they are correct, then a rather
large fraction of BBH mergers would be taking place within the discs of AGN.

#### Dynamical versus field rates

If we assume that GRB 191019A were created by a compact object binary it is
also relevant to consider the probability that it arises via field binary
evolution, or via dynamical interactions. Published rates mandel22  for field
interactions span a range from 0.3–8900 Gpc-3 yr-1 and nuclear interactions
from 0.004–1.5 Gpc-3 yr-1 or $<400$ Gpc-3 yr-1 considering gaseous discs. This
large range of rates makes it difficult to make any robust prediction as to
the fraction of mergers which form via each channel. However, median values
would imply a ratio of several hundred field binary mergers per dynamically
formed nuclear system.

This is consistent with the fact that no well localised (sub-arcsecond) short
GRBs are apparently consistent with the nuclei of their hosts. Indeed,
population synthesis predictions suggest that very few mergers should be
nuclear Belczynski06 ; fong22 . Wiggins et al. Wiggins18  find that less than
1% of mergers originate at $<100$ pc of the nucleus of their host galaxies.
Therefore, within the uncertainty of the models, the fraction of mergers
formed via binary evolution is similar to the fraction of mergers that form
dynamically in the nuclear region of host galaxies.

However, the properties of the galaxy in the case of GRB 191019A offer strong
suggestions that the merger is dynamical, and not of a field binary. Firstly,
in ancient galaxies we primarily observe the population of field compact
object mergers with long delay times. These will travel further from their
birth sites, and so have larger offsets than for binaries with short merger
times. Indeed, in the short-GRB population there are apparently larger offsets
to early type hosts fong22 ; nugent22 . Therefore, the presence of GRB 191019A
in the nucleus of an ancient host already suggests a more likely dynamical
origin.

Secondly, not all galaxies have identical interaction rates in their cores.
Those interaction rates are a sensitive function of the core density, of the
properties of its nuclear star cluster (e.g. mass, the presence of a disc),
and of the characteristics of its black hole population. Galaxies with similar
properties to the host of GRB 191019A (in terms of Lick indices) are over-
represented as the hosts of tidal disruption events by up to two orders of
magnitude (representing 2.3% of the observed SDSS population but 75% of TDE
hosts French17 ). The TDE rate is influenced by the scattering of stars into
the loss cone of the supermassive black hole. It is not straightforward to
scale from the TDE rate to the dynamical formation rate of compact objects,
however, it is reasonable to assume that the enhanced TDE rate also leads to
increased rates of other dynamical interactions.

Hence, the probability of a field binary arising in the nuclear regions of an
ancient galaxy in which the interaction rates are very high, is substantially
lower than arising in any galactic nucleus. The dynamical probability would
also increase for systems including black holes, relative to those with
neutron stars (BH-NS, BH-WD). We therefore conclude that in the case of GRB
191019A a dynamical origin is more likely than a field system.

## Declarations

Acknowledgments

A.J. Levan, D.B. Malesani and N.R. Tanvir are supported by the European
Research Council (ERC) under the European Union’s Horizon 2020 research and
innovation programme (grant agreement No. 725246). D.B.M. also acknowledges
research grant 19054 from VILLUM FONDEN. M. Nicholl and B. Gompertz are
supported by the European Research Council (ERC) under the European Union’s
Horizon 2020 research and innovation programme (grant agreement No. 948381).
M. Nicholl acknowledges a Turing Fellowship. The Fong Group at Northwestern
acknowledges support by the National Science Foundation under grant Nos.
AST-1814782, AST-1909358 and CAREER grant No. AST-2047919. W.F. gratefully
acknowledges support by the David and Lucile Packard Foundation. K.E. Heintz
acknowledges support from the Carlsberg Foundation Reintegration Fellowship
Grant CF21-0103. J. Hjorth was supported by a VILLUM FONDEN Investigator grant
(project number 16599). G. Lamb is supported by the UK Science Technology and
Facilities Council grant, ST/S000453/1. A. Inkenhaag acknowledges the research
programme Athena with project number 184.034.002, which is financed by the
Dutch Research Council (NWO). K. Bhirombhakdi was supported by STScI HST
General Observer Programs 16548 and 16051 through a grant from STScI under
NASA contract NAS5-26555. The Cosmic Dawn Center is funded by the Danish
National Research Foundation under grant No. 140. G. Fragione acknowledges
support from NASA Grant 80NSSC21K1722 and NSF Grant AST-2108624 at
Northwestern University. I. Mandel acknowledges support from the Australian
Research Council through the Centre of Excellence for Gravitational Wave
Discovery (OzGrav), project number CE17010004, and through Future Fellowship
FT190100574.

Partly based on observations made with the Nordic Optical Telescope, under
programs 58-502 and 61-503, owned in collaboration by the University of Turku
and Aarhus University, and operated jointly by Aarhus University, the
University of Turku and the University of Oslo, representing Denmark, Finland
and Norway, the University of Iceland and Stockholm University at the
Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de
Astrofísica de Canarias. And on observations obtained at the international
Gemini Observatory (program IDs GS-2019B-DD-106 and GS-2019B-FT-209), a
program of NOIRLab, which is managed by the Association of Universities for
Research in Astronomy (AURA) under a cooperative agreement with the National
Science Foundation on behalf of the Gemini Observatory partnership: the
National Science Foundation (United States), National Research Council
(Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio
de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência,
Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space
Science Institute (Republic of Korea). Processed using the Gemini IRAF package
and DRAGONS (Data Reduction for Astronomy from Gemini Observatory North and
South). And on observations made with the NASA/ESA Hubble Space Telescope
obtained from the Space Telescope Science Institute, which is operated by the
Association of Universities for Research in Astronomy, Inc., under NASA
contract NAS 5–26555. These observations are associated with program #16051
and 16458. This work made use of data supplied by the UK Swift Science Data
Centre at the University of Leicester.

The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been
made possible through contributions by the Institute for Astronomy, the
University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society
and its participating institutes, the Max Planck Institute for Astronomy,
Heidelberg and the Max Planck Institute for Extraterrestrial Physics,
Garching, The Johns Hopkins University, Durham University, the University of
Edinburgh, the Queen’s University Belfast, the Harvard-Smithsonian Center for
Astrophysics, the Las Cumbres Observatory Global Telescope Network
Incorporated, the National Central University of Taiwan, the Space Telescope
Science Institute, the National Aeronautics and Space Administration under
Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA
Science Mission Directorate, the National Science Foundation Grant No.
AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), the
Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation.
Partly based on observations obtained as part of the VISTA Hemisphere Survey,
ESO Progam, 179.A-2010 (PI: McMahon). This publication makes use of data
products from the Wide-field Infrared Survey Explorer, which is a joint
project of the University of California, Los Angeles, and the Jet Propulsion
Laboratory/California Institute of Technology, funded by the National
Aeronautics and Space Administration.

Data Availability

The majority of data generated or analysed during this study are included in
this published article (and its supplementary information files). Gamma-ray
and X-ray data from _Swift_ may be downloaded from the UK _Swift_ Science Data
Centre at https://www.swift.ac.uk/. HST, Gemini and NOT data can be downloaded
from the relevant archives at https://archive.stsci.edu,
https://archive.gemini.edu,
https://www.not.iac.es/observing/forms/fitsarchive/.

Code Availability

The Prospector stellar population modeling code is available at
https://github.com/bd-j/prospector. The IRAF and python scripts necessary for
HST data reduction can be obtained via astroconda, and IRAF (including the
relevant Gemini IRAF packages) from http://www.gemini.edu/observing/phase-
iii/understanding-and-processing-data/data-processing-software/gemini-iraf-
general.

Conflict of interest

We declare no conflicts of interests.

Authors’ Contributions

AJL obtained, reduced and analysed observations and wrote the text. DBM
obtained and reduced the NOT observations, performed subtractions and
photometry and contributed to analysis and interpretation. BPG undertook the
Swift BAT and XRT analysis and contributed to analysis and interpretation. AEN
performed analysis of the host galaxy with Prospector. MN contributed to the
light curve and TDE sections and spectral analysis. SRO analysed the UVOT
data. DAP contributed to the NOT observations and interpretation. JR worked
with the Gemini observations, photometry and subtractions. BDM contributed to
the theoretical discussion and interpretation. SS provided the comparison
between the X-ray/gamma-ray light curves of GRB 191019A and other bursts. ERS
worked on population modelling of the host galaxy. AI performed the fit of the
spectrum with pPXF. AAC investigated the host population and contributed to
interpretation. KB and AF worked on the HST observations and provided
comments. AdUP worked on the NOT observations and commented on the text. WF
worked on the interpretation. GF provided theoretical interpretation. JPUF led
the first NOT observations and provided comments. NG worked on the offset
implications. KEH worked on the NOT data and interpretation. JH worked on
interpretation and text. PGJ worked on the interpretation, in particular with
regard to TDE possibilities. GL worked on the interpretation, IM provided
theoretical input. JS and PJ worked on the NOT data and provided comments. NRT
was involved in the NOT, Gemini and HST observations.

Supplementary Information

Supplementary Information is available for this paper.

## Supplementary Methods

## Supplementary Discussion

## Supplementary Tables

Table 1: Optical observations of the counterpart of GRB 191019A. The magnitude
given is the integrated magnitude of host + afterglow, while the afterglow
column provides the afterglow flux. An (s) indicates this flux is measured in
a subtracted image while other magnitudes are based on the subtraction of the
mean host galaxy flux in a large aperture. Magnitudes have not been corrected
for foreground extinction of $E(B-V)=0.04$ mag

.

Date | MJD | $\Delta T$ | Telescope | Band | Exptime | Magnitude | Afterglow
---|---|---|---|---|---|---|---
|  | (days) |  |  | (s) | (AB) |  ($\mu$Jy)
2019-10-19 | 58775.82559 | 0.188 | NOT | $i$ | 600 |  18.585 $\pm$ 0.022 |  9.12$\pm$0.36 (s)
2019-10-19 | 58775.83911 | 0.205 | NOT | $g$ | 900 |  19.806 $\pm$ 0.014 |  $5.40\pm 0.16$ (s)
2019-10-19 | 58775.83911 | 0.217 | NOT | $r$ | 900 |  19.028 $\pm$ 0.018 |  $7.05\pm 0.21$ (s)
2019-10-19 | 58775.86312 | 0.229 | NOT | $z$ | 1000 |  19.212 $\pm$ 0.014 |  $13.30\pm 0.40$ (s)
2019-10-22 | 58778.87524 | 3.242 | NOT | $i$ | 1500 |  18.646 $\pm$ 0.028 |  1.30 $\pm$ 3.66
2019-10-29 | 58785.85191 | 10.218 | NOT | $i$ | 900 |  18.678 $\pm$ 0.029 |  -2.36 $\pm$ 3.69
2019-10-29 | 58785.86350 | 10.230 | NOT | $g$ | 900 |  19.998 $\pm$ 0.014 |  0.017 $\pm$ 0.509
2019-10-29 | 58785.87499 | 10.241 | NOT | $r$ | 900 |  19.093 $\pm$ 0.021 |  1.57 $\pm$ 1.93
2019-10-29 | 58785.88748 | 10.254 | NOT | $z$ | 1000 |  19.391 $\pm$ 0.017 | —
2019-10-31 | 58787.03036 | 11.397 | Gemini-S | $g$ | 900 |  19.940 $\pm$ 0.006 |  -0.14 $\pm$ 0.29
2019-10-31 | 58787.04344 | 11.410 | Gemini-S | $r$ | 900 |  19.039 $\pm$ 0.004 |  0.82 $\pm$ 0.48
2019-10-31 | 58787.18344 | 11.550 | Gemini-S | $z$ | 900 |  18.348 $\pm$ 0.008 |  1.04 $\pm$ 1.18
2019-11-10 | 58797.04364 | 21.410 | Gemini-S | $z$ | 720 |  18.383 $\pm$ 0.010 |  -4.23 $\pm$ 1.78
2019-11-22 | 58809.82539 | 34.192 | NOT | $i$ | 3000 |  18.648 $\pm$ 0.034 |  1.06 $\pm$ 4.39
2019-11-22 | 58809.84448 | 34.211 | NOT | $r$ | 3000 |  19.110 $\pm$ 0.021 |  0.27 $\pm$ 1.91
2019-11-26 | 58813.02799 | 37.394 | Gemini-S | $g$ | 900 |  19.938 $\pm$ 0.006 |  -0.08 $\pm$ 0.29
2019-11-26 | 58813.03911 | 37.405 | Gemini-S | $r$ | 900 |  19.060 $\pm$ 0.004 |  -0.85 $\pm$ 0.46
2019-11-26 | 58813.05029 | 37.417 | Gemini-S | $z$ | 600 |  18.368 $\pm$ 0.009 |  -1.99 $\pm$ 1.65
2019-12-09 | 58826.02618 | 50.393 | Gemini-S | $z$ | 780 |  18.336 $\pm$ 0.011 |  2.88 $\pm$ 2.00
2019-12-16 | 58833.04820 | 57.415 | Gemini-S | $g$ | 750 |  19.931 $\pm$ 0.007 |  0.17 $\pm$ 0.32
2019-12-16 | 58833.05932 | 57.426 | Gemini-S | $r$ | 750 |  19.047 $\pm$ 0.005 |  0.18 $\pm$ 0.54
2019-12-16 | 58833.07047 | 57.437 | Gemini-S | $z$ | 750 |  18.342 $\pm$ 0.009 |  1.95 $\pm$ 1.68
2019-12-17 | 58834.05827 | 58.425 | Gemini-S | $g$ | 750 |  19.936 $\pm$ 0.006 |  -0.01 $\pm$ 0.29
2019-12-17 | 58834.07159 | 58.438 | Gemini-S | $r$ | 750 |  19.041 $\pm$ 0.004 |  0.66 $\pm$ 0.47
2019-12-17 | 58834.08246 | 58.449 | Gemini-S | $z$ | 750 |  18.353 $\pm$ 0.011 |  0.27 $\pm$ 1.97
2019-12-21 | 58838.05466 | 62.421 | Gemini-S | $g$ | 750 |  19.955 $\pm$ 0.006 |  -0.67 $\pm$ 0.29
2019-12-21 | 58838.06358 | 62.430 | Gemini-S | $r$ | 750 |  19.044 $\pm$ 0.005 |  0.42 $\pm$ 0.54
2019-12-21 | 58838.07468 | 62.441 | Gemini-S | $z$ | 750 |  18.347 $\pm$ 0.010 |  1.18 $\pm$ 1.83
2019-12-30 | 58847.03322 | 71.400 | Gemini-S | $g$ | 800 |  19.915 $\pm$ 0.013 |  0.74 $\pm$ 0.53
2019-12-30 | 58847.04607 | 71.412 | Gemini-S | $r$ | 800 |  19.065 $\pm$ 0.006 |  -1.25 $\pm$ 0.61
2020-01-01 | 58849.04549 | 73.412 | Gemini-S | $z$ | 750 |  18.362 $\pm$ 0.007 |  -1.10 $\pm$ 1.38
2020-06-21 | 59021.15875 | 245.525 | NOT | $r$ | 1800 |  19.138 $\pm$ 0.010 |  -1.83 $\pm$ 1.13
2020-06-21 | 59021.18441 | 245.551 | NOT | $g$ | 2400 |  19.999 $\pm$ 0.010 |  -0.017 $\pm$ 0.364

Table 2: Log of Swift-UVOT observations of GRB 191019A. The given magnitudes are a combination of afterglow + host galaxy. The afterglow flux densities are the remaining afterglow flux after the subtraction of the final epoch values for the White, $V$, $B$ and $U$ bands. For the UV filters (UVW1, UVM2, UVW2) we have HST observations which demonstrate that the host galaxy is much fainter that these detections. Therefore, rather than subtract the (low signal to noise) late UVOT observations, we subtract instead a source of $1.7\pm 0.5$ $\mu$Jy (with the error larger than those measured in the HST observations to reflect uncertainties in the precise band). The magnitudes are indicated in the table with an (a). Magnitudes have not been corrected for foreground extinction of $E(B-V)=0.04$ mag. MJD | $\Delta T$ | Telescope | Band |  $t_{1/2}$ (s) | Magnitude | Afterglow
---|---|---|---|---|---|---
| (days) |  |  | (s) | (AB) |  ($\mu$Jy)
58775.673 | 0.0389 | UVOT | White | 75 | $20.85^{+0.39}_{-0.29}$ | $9.26\pm 4.29$
58775.690 | 0.0562 | UVOT | White | 100 | $20.48^{+0.16}_{-0.14}$ | $14.59\pm 3.73$
58775.962 | 0.3279 | UVOT | White | 343 | $21.02^{+0.13}_{-0.12}$ | $4.01\pm 1.50$
58781.722 | 6.0880 | UVOT | White | 40666 | $21.24^{+0.04}_{-0.04}$ | $1.52\pm 0.53$
58961.436 | 185.8020 | UVOT | White | 37620 | $21.43^{+0.14}_{-0.13}$ | —
58775.675 | 0.0410 | UVOT | $V$ | 100 | $18.90^{+0.29}_{-0.23}$ | $44.92\pm 26.64$
58775.695 | 0.0609 | UVOT | $V$ | 100 | $19.11^{+0.31}_{-0.24}$ | $27.4\pm 24.17$
58775.811 | 0.1769 | UVOT | $V$ | 80 | $19.93^{+0.82}_{-0.46}$ | $-15.58\pm 24.38$
58955.963 | 179.3290 | UVOT | $V$ | 589 | $19.55^{+0.30}_{-0.24}$ | —
58775.688 | 0.0538 | UVOT | $B$ | 100 | $20.52^{+0.50}_{-0.34}$ | $10.09\pm 10.71$
58775.829 | 0.1952 | UVOT | $B$ | 333 | $20.52^{+0.25}_{-0.21}$ | $9.74\pm 6.31$
58775.952 | 0.3186 | UVOT | $B$ | 453 | $20.54^{+0.22}_{-0.18}$ | $9.52\pm 5.56$
58776.781 | 1.1474 | UVOT | $B$ | 9405 | $20.68^{+0.16}_{-0.14}$ | $7.21\pm 3.54$
58959.945 | 184.3120 | UVOT | $B$ | 444 | $20.95^{+0.66}_{-0.41}$ | —
58775.685 | 0.0514 | UVOT | $U$ | 100 | $21.10^{+0.41}_{-0.30}$ | $9.89\pm 5.17$
58775.743 | 0.1096 | UVOT | $U$ | 73 | $21.22^{+0.57}_{-0.37}$ | $8.47\pm 5.72$
58775.942 | 0.3081 | UVOT | $U$ | 453 | $21.81^{+0.39}_{-0.29}$ | $3.58\pm 2.75$
58776.781 | 1.1475 | UVOT | $U$ | 9670 | $22.28^{+0.31}_{-0.24}$ | $1.27\pm 1.50$
58961.638 | 186.0050 | UVOT | $U$ | 26238 | $22.42^{+1.42}_{-0.60}$ | —
58775.683 | 0.0491 | UVOT | UVW1 | 100 | $21.282^{+0.41}_{-0.30}$ |  $9.31\pm 3.46$a
58775.699 | 0.0654 | UVOT | UVW1 | 74 | $21.27^{+0.48}_{-0.33}$ |  $9.44\pm 3.98$a
58775.890 | 0.2564 | UVOT | UVW1 | 789 | $22.40^{+0.50}_{-0.34}$ |  $2.22\pm 1.54$a
58776.006 | 0.3724 | UVOT | UVW1 | 222 | $21.83^{+0.46}_{-0.32}$ |  $4.94\pm 2.33$a
58962.195 | 186.5620 | UVOT | UVW1 | 500 | $23.21^{+1.74}_{-0.64}$ | —
58775.677 | 0.0435 | UVOT | UVM2 | 100 | $22.36^{+1.12}_{-0.54}$ |  $2.43\pm 2.69$a
58775.697 | 0.0633 | UVOT | UVM2 | 100 | $21.68^{+0.57}_{-0.37}$ |  $6.04\pm 3.21$a
58775.876 | 0.2419 | UVOT | UVM2 | 450 | $23.52^{+1.37}_{-0.59}$ |  $-0.28\pm 1.13$a
58968.894 | 193.2610 | UVOT | UVM2 | 400 | $23.11^{+0.94}_{-0.50}$ | —
58775.692 | 0.0585 | UVOT | UVW2 | 100 | $22.06^{+0.59}_{-0.38}$ |  $3.73\pm 2.33$a
58775.762 | 0.1280 | UVOT | UVW2 | 404 | $22.02^{+0.26}_{-0.21}$ |  $3.94\pm 1.3$a
58959.813 | 184.1790 | UVOT | UVW2 | 444 | $23.46^{+1.40}_{-0.59}$ | —
Table 3: Multiband photometry of the host galaxy of GRB 191019A. Filter |  $\lambda$ (nm) | Magnitude (AB) | Origin
---|---|---|---
F225W | 235.8 | 23.32 $\pm$ 0.07 | This work
F275W | 270.3 | 23.43 $\pm$ 0.04 | This work
$g$ | 481.0 | 20.17 $\pm$ 0.02 | Pan-STARRS Chambers+16
$r$ | 617.0 | 19.18 $\pm$ 0.01 | Pan-STARRS Chambers+16
$i$ | 752.0 | 18.76 $\pm$ 0.01 | Pan-STARRS Chambers+16
$z$ | 866.0 | 18.58 $\pm$ 0.01 | Pan-STARRS Chambers+16
$y$ | 962.0 | 18.53 $\pm$ 0.025 | Pan-STARRS Chambers+16
$Y$ | 1020.0 | 18.21 $\pm$ 0.057 | VHS McMahon+2013
$J$ | 1252 | 18.096 $\pm$ 0.079 | VHS McMahon+2013
$K_{s}$ | 2147 | 17.547 $\pm$ 0.09 | VHS McMahon+2013
WISE W1 | 3353 | 18.338 $\pm$ 0.047 | WISE WISE_Wright+10
WISE W2 | 4603 | 18.729 $\pm$ 0.112 | WISE WISE_Wright+10

## References

  *   * (1) Hjorth, J., Sollerman, J., Møller, P., Fynbo, J.P.U., Woosley, S.E., Kouveliotou, C., Tanvir, N.R., Greiner, J., Andersen, M.I., Castro-Tirado, A.J., Castro Cerón, J.M., Fruchter, A.S., Gorosabel, J., Jakobsson, P., Kaper, L., Klose, S., Masetti, N., Pedersen, H., Pedersen, K., Pian, E., Palazzi, E., Rhoads, J.E., Rol, E., van den Heuvel, E.P.J., Vreeswijk, P.M., Watson, D., Wijers, R.A.M.J.: A very energetic supernova associated with the $\gamma$-ray burst of 29 March 2003. Nature 423(6942), 847–850 (2003) arXiv:astro-ph/0306347 [astro-ph]. https://doi.org/10.1038/nature01750
  * (2) Rastinejad, J.C., Gompertz, B.P., Levan, A.J., Fong, W., Nicholl, M., Lamb, G.P., Malesani, D.B., Nugent, A.E., Oates, S.R., Tanvir, N.R., de Ugarte Postigo, A., Kilpatrick, C.D., Moore, C.J., Metzger, B.D., Ravasio, M.E., Rossi, A., Schroeder, G., Jencson, J., Sand, D.J., Smith, N., Agüí Fernández, J.F., Berger, E., Blanchard, P.K., Chornock, R., Cobb, B.E., De Pasquale, M., Fynbo, J.P.U., Izzo, L., Kann, D.A., Laskar, T., Marini, E., Paterson, K., Rouco Escorial, A., Sears, H.M., Thöne, C.C.: A Kilonova Following a Long-Duration Gamma-Ray Burst at 350 Mpc. arXiv e-prints, 2204–10864 (2022) arXiv:2204.10864 [astro-ph.HE]
  * (3) Troja, E., Fryer, C.L., O’Connor, B., Ryan, G., Dichiara, S., Kumar, A., Ito, N., Gupta, R., Wollaeger, R., Norris, J.P., Kawai, N., Butler, N., Aryan, A., Misra, K., Hosokawa, R., Murata, K.L., Niwano, M., Pandey, S.B., Kutyrev, A., van Eerten, H.J., Chase, E.A., Hu, Y.-D., Caballero-Garcia, M.D., Castro-Tirado, A.J.: A long gamma-ray burst from a merger of compact objects. arXiv e-prints, 2209–03363 (2022) arXiv:2209.03363 [astro-ph.HE]
  * (4) Yang, J., Ai, S., Zhang, B.-B., Zhang, B., Liu, Z.-K., Wang, X.I., Yang, Y.-H., Yin, Y.-H., Li, Y., Lü, H.-J.: A long-duration gamma-ray burst with a peculiar origin. arXiv e-prints, 2204–12771 (2022) arXiv:2204.12771 [astro-ph.HE]
  * (5) Grindlay, J., Portegies Zwart, S., McMillan, S.: Short gamma-ray bursts from binary neutron star mergers in globular clusters. Nature Physics 2, 116–119 (2006) astro-ph/0512654. https://doi.org/10.1038/nphys214
  * (6) Fragione, G., Grishin, E., Leigh, N.W.C., Perets, H.B., Perna, R.: Black hole and neutron star mergers in galactic nuclei. MNRAS 488(1), 47–63 (2019) arXiv:1811.10627 [astro-ph.GA]. https://doi.org/10.1093/mnras/stz1651
  * (7) McKernan, B., Ford, K.E.S., O’Shaughnessy, R.: Black hole, neutron star, and white dwarf merger rates in AGN discs. MNRAS 498(3), 4088–4094 (2020) arXiv:2002.00046 [astro-ph.HE]. https://doi.org/10.1093/mnras/staa2681
  * (8) O’Leary, R.M., Meiron, Y., Kocsis, B.: Dynamical Formation Signatures of Black Hole Binaries in the First Detected Mergers by LIGO. ApJ 824(1), 12 (2016) arXiv:1602.02809 [astro-ph.HE]. https://doi.org/10.3847/2041-8205/824/1/L12
  * (9) Stone, N.C., Metzger, B.D.: Rates of stellar tidal disruption as probes of the supermassive black hole mass function. MNRAS 455(1), 859–883 (2016) arXiv:1410.7772 [astro-ph.HE]. https://doi.org/10.1093/mnras/stv2281
  * (10) Perna, R., Lazzati, D., Cantiello, M.: Electromagnetic Signatures of Relativistic Explosions in the Disks of Active Galactic Nuclei. ApJ 906(2), 7 (2021) arXiv:2011.08873 [astro-ph.HE]. https://doi.org/10.3847/2041-8213/abd319
  * (11) Lazzati, D., Soares, G., Perna, R.: Prompt Emission of Gamma-Ray Bursts in the High-density Environment of Active Galactic Nuclei Accretion Disks. arXiv e-prints, 2209–14308 (2022) arXiv:2209.14308 [astro-ph.HE]
  * (12) Galama, T.J., Vreeswijk, P.M., van Paradijs, J., Kouveliotou, C., Augusteijn, T., Böhnhardt, H., Brewer, J.P., Doublier, V., Gonzalez, J.-F., Leibundgut, B., Lidman, C., Hainaut, O.R., Patat, F., Heise, J., in’t Zand, J., Hurley, K., Groot, P.J., Strom, R.G., Mazzali, P.A., Iwamoto, K., Nomoto, K., Umeda, H., Nakamura, T., Young, T.R., Suzuki, T., Shigeyama, T., Koshut, T., Kippen, M., Robinson, C., de Wildt, P., Wijers, R.A.M.J., Tanvir, N., Greiner, J., Pian, E., Palazzi, E., Frontera, F., Masetti, N., Nicastro, L., Feroci, M., Costa, E., Piro, L., Peterson, B.A., Tinney, C., Boyle, B., Cannon, R., Stathakis, R., Sadler, E., Begam, M.C., Ianna, P.: An unusual supernova in the error box of the $\gamma$-ray burst of 25 April 1998. Nature 395(6703), 670–672 (1998) arXiv:astro-ph/9806175 [astro-ph]. https://doi.org/10.1038/27150
  * (13) Abbott, B.P., Abbott, R., Abbott, T.D., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P., Adhikari, R.X., Adya, V.B., Affeldt, C., Afrough, M., Agarwal, B., Agathos, M., Agatsuma, K., Aggarwal, N., Aguiar, O.D., Aiello, L., et al.: GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral. Phys. Rev. Lett. 119(16), 161101 (2017) arXiv:1710.05832 [gr-qc]. https://doi.org/10.1103/PhysRevLett.119.161101
  * (14) Simpson, K.K., Barthelmy, S.D., Gropp, J.D., Lien, A.Y., Page, K.L., Palmer, D.M., Tohuvavohu, A., Neil Gehrels Swift Observatory Team: GRB 191019A: Swift detection of a burst. GRB Coordinates Network 26031, 1 (2019)
  * (15) Krimm, H.A., Barthelmy, S.D., Cummings, J.R., Laha, S., Lien, A.Y., Markwardt, C.B., Palmer, D.M., Sakamoto, T., Simpson, K.K., Stamatikos, M., Ukwatta, T.N.: GRB 191019A: Swift-BAT refined analysis. GRB Coordinates Network 26046, 1 (2019)
  * (16) Evans, P.A., Osborne, J.P., Burrows, D.N., Kennea, J.A., Campana, S., Cusumano, G., Swift-XRT Team: GRB 191019A: Swift-XRT observations. GRB Coordinates Network 26034, 1 (2019)
  * (17) Perley, D.A., Malesani, D.B., Levan, A.J., Fynbo, J.P.U., Djupvik, A.A., et al.: GRB 191019A: NOT optical afterglow and host association confirmation. GRB Coordinates Network 26062, 1 (2019)
  * (18) Perley, D.A., Fremling, C., Sollerman, J., Miller, A.A., Dahiwale, A.S., Sharma, Y., Bellm, E.C., Biswas, R., Brink, T.G., Bruch, R.J., De, K., Dekany, R., Drake, A.J., Duev, D.A., Filippenko, A.V., Gal-Yam, A., Goobar, A., Graham, M.J., Graham, M.L., Ho, A.Y.Q., Irani, I., Kasliwal, M.M., Kim, Y.-L., Kulkarni, S.R., Mahabal, A., Masci, F.J., Modak, S., Neill, J.D., Nordin, J., Riddle, R.L., Soumagnac, M.T., Strotjohann, N.L., Schulze, S., Taggart, K., Tzanidakis, A., Walters, R.S., Yan, L.: The Zwicky Transient Facility Bright Transient Survey. II. A Public Statistical Sample for Exploring Supernova Demographics. ApJ 904(1), 35 (2020) arXiv:2009.01242 [astro-ph.HE]. https://doi.org/%****␣nature.tex␣Line␣1500␣****10.3847/1538-4357/abbd98
  * (19) Nicholl, M., Lanning, D., Ramsden, P., Mockler, B., Lawrence, A., Short, P., Ridley, E.J.: Systematic light curve modelling of TDEs: statistical differences between the spectroscopic classes. arXiv e-prints, 2201–02649 (2022) arXiv:2201.02649 [astro-ph.HE]
  * (20) Hammerstein, E., van Velzen, S., Gezari, S., Cenko, S.B., Yao, Y., Ward, C., Frederick, S., Villanueva, N., Somalwar, J.J., Graham, M.J., Kulkarni, S.R., Stern, D., Bellm, E.C., Dekany, R., Drake, A.J., Groom, S.L., Kasliwal, M.M., Kool, E.C., Masci, F.J., Medford, M.S., van Roestel, J.: The Final Season Reimagined: 30 Tidal Disruption Events from the ZTF-I Survey. arXiv e-prints, 2203–01461 (2022) arXiv:2203.01461 [astro-ph.HE]
  * (21) Villar, V.A., Guillochon, J., Berger, E., Metzger, B.D., Cowperthwaite, P.S., Nicholl, M., Alexand er, K.D., Blanchard, P.K., Chornock, R., Eftekhari, T., Fong, W., Margutti, R., Williams, P.K.G.: The Combined Ultraviolet, Optical, and Near-infrared Light Curves of the Kilonova Associated with the Binary Neutron Star Merger GW170817: Unified Data Set, Analytic Models, and Physical Implications. ApJL 851(1), 21 (2017) arXiv:1710.11576 [astro-ph.HE]. https://doi.org/10.3847/2041-8213/aa9c84
  * (22) Kormendy, J., Ho, L.C.: Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies. ARA&A 51(1), 511–653 (2013) arXiv:1304.7762 [astro-ph.CO]. https://doi.org/10.1146/annurev-astro-082708-101811
  * (23) Fong, W.-f., Nugent, A.E., Dong, Y., Berger, E., Paterson, K., Chornock, R., Levan, A., Blanchard, P., Alexander, K.D., Andrews, J., Cobb, B.E., Cucchiara, A., Fox, D., Fryer, C.L., Gordon, A.C., Kilpatrick, C.D., Lunnan, R., Margutti, R., Miller, A., Milne, P., Nicholl, M., Perley, D., Rastinejad, J., Rouco Escorial, A., Schroeder, G., Smith, N., Tanvir, N., Terreran, G.: Short GRB Host Galaxies I: Photometric and Spectroscopic Catalogs, Host Associations, and Galactocentric Offsets. arXiv e-prints, 2206–01763 (2022) arXiv:2206.01763 [astro-ph.GA]
  * (24) Ye, C.S., Fong, W.-f., Kremer, K., Rodriguez, C.L., Chatterjee, S., Fragione, G., Rasio, F.A.: On the Rate of Neutron Star Binary Mergers from Globular Clusters. ApJ 888(1), 10 (2020) arXiv:1910.10740 [astro-ph.HE]. https://doi.org/10.3847/2041-8213/ab5dc5
  * (25) Antonini, F., Rasio, F.A.: Merging Black Hole Binaries in Galactic Nuclei: Implications for Advanced-LIGO Detections. ApJ 831(2), 187 (2016) arXiv:1606.04889 [astro-ph.HE]. https://doi.org/10.3847/0004-637X/831/2/187
  * (26) Tagawa, H., Haiman, Z., Kocsis, B.: Formation and Evolution of Compact-object Binaries in AGN Disks. ApJ 898(1), 25 (2020) arXiv:1912.08218 [astro-ph.GA]. https://doi.org/10.3847/1538-4357/ab9b8c
  * (27) French, K.D., Arcavi, I., Zabludoff, A.: The Post-starburst Evolution of Tidal Disruption Event Host Galaxies. ApJ 835(2), 176 (2017) arXiv:1609.04755 [astro-ph.GA]. https://doi.org/10.3847/1538-4357/835/2/176
  * (28) Gompertz, B.P., Ravasio, M.E., Nicholl, M., Levan, A.J., Metzger, B.D., Oates, S.R., Lamb, G.P., Fong, W., Malesani, D.B., Rastinejad, J.C., Tanvir, N.R., Evans, P.A., Jonker, P.G., Page, K.L., Pe’er, A.: A minute-long merger-driven gamma-ray burst from fast-cooling synchrotron emission. arXiv e-prints, 2205–05008 (2022) arXiv:2205.05008 [astro-ph.HE]
  * (29) Perley, D.A., Metzger, B.D., Granot, J., Butler, N.R., Sakamoto, T., Ramirez-Ruiz, E., Levan, A.J., Bloom, J.S., Miller, A.A., Bunker, A., Chen, H.-W., Filippenko, A.V., Gehrels, N., Glazebrook, K., Hall, P.B., Hurley, K.C., Kocevski, D., Li, W., Lopez, S., Norris, J., Piro, A.L., Poznanski, D., Prochaska, J.X., Quataert, E., Tanvir, N.: GRB 080503: Implications of a Naked Short Gamma-Ray Burst Dominated by Extended Emission. ApJ 696(2), 1871–1885 (2009) arXiv:0811.1044 [astro-ph]. https://doi.org/10.1088/0004-637X/696/2/1871
  * (30) Bucciantini, N., Metzger, B.D., Thompson, T.A., Quataert, E.: Short gamma-ray bursts with extended emission from magnetar birth: jet formation and collimation. MNRAS 419(2), 1537–1545 (2012) arXiv:1106.4668 [astro-ph.HE]. https://doi.org/%****␣nature.tex␣Line␣1800␣****10.1111/j.1365-2966.2011.19810.x
  * (31) Lu, W., Quataert, E.: Late-time accretion in neutron star mergers: implications for short gamma-ray bursts and kilonovae. arXiv e-prints, 2208–04293 (2022) arXiv:2208.04293 [astro-ph.HE]
  * (32) King, A., Olsson, E., Davies, M.B.: A new type of long gamma-ray burst. MNRAS 374(1), 34–36 (2007) arXiv:astro-ph/0610452 [astro-ph]. https://doi.org/10.1111/j.1745-3933.2006.00259.x
  * (33) McBrien, O.R., Smartt, S.J., Chen, T.-W., Inserra, C., Gillanders, J.H., Sim, S.A., Jerkstrand, A., Rest, A., Valenti, S., Roy, R., Gromadzki, M., Taubenberger, S., Flörs, A., Huber, M.E., Chambers, K.C., Gal-Yam, A., Young, D.R., Nicholl, M., Kankare, E., Smith, K.W., Maguire, K., Mandel, I., Prentice, S., Rodríguez, Ó., Pineda Garcia, J., Gutiérrez, C.P., Galbany, L., Barbarino, C., Clark, P.S.J., Sollerman, J., Kulkarni, S.R., De, K., Buckley, D.A.H., Rau, A.: SN2018kzr: A Rapidly Declining Transient from the Destruction of a White Dwarf. ApJ 885(1), 23 (2019) arXiv:1909.04545 [astro-ph.HE]. https://doi.org/10.3847/2041-8213/ab4dae
  * (34) Gillanders, J.H., Sim, S.A., Smartt, S.J.: AT2018kzr: the merger of an oxygen-neon white dwarf and a neutron star or black hole. MNRAS 497(1), 246–262 (2020) arXiv:2007.12110 [astro-ph.HE]. https://doi.org/10.1093/mnras/staa1822
  * (35) Fynbo, J.P.U., Watson, D., Thöne, C.C., Sollerman, J., Bloom, J.S., Davis, T.M., Hjorth, J., Jakobsson, P., Jørgensen, U.G., Graham, J.F., Fruchter, A.S., Bersier, D., Kewley, L., Cassan, A., Castro Cerón, J.M., Foley, S., Gorosabel, J., Hinse, T.C., Horne, K.D., Jensen, B.L., Klose, S., Kocevski, D., Marquette, J.-B., Perley, D., Ramirez-Ruiz, E., Stritzinger, M.D., Vreeswijk, P.M., Wijers, R.A.M., Woller, K.G., Xu, D., Zub, M.: No supernovae associated with two long-duration $\gamma$-ray bursts. Nature 444(7122), 1047–1049 (2006) arXiv:astro-ph/0608313 [astro-ph]. https://doi.org/10.1038/nature05375
  * (36) Gal-Yam, A., Fox, D.B., Price, P.A., Ofek, E.O., Davis, M.R., Leonard, D.C., Soderberg, A.M., Schmidt, B.P., Lewis, K.M., Peterson, B.A., Kulkarni, S.R., Berger, E., Cenko, S.B., Sari, R., Sharon, K., Frail, D., Moon, D.-S., Brown, P.J., Cucchiara, A., Harrison, F., Piran, T., Persson, S.E., McCarthy, P.J., Penprase, B.E., Chevalier, R.A., MacFadyen, A.I.: A novel explosive process is required for the $\gamma$-ray burst GRB 060614. Nature 444(7122), 1053–1055 (2006) arXiv:astro-ph/0608257 [astro-ph]. https://doi.org/10.1038/nature05373
  * (37) Gehrels, N., Norris, J.P., Barthelmy, S.D., Granot, J., Kaneko, Y., Kouveliotou, C., Markwardt, C.B., Mészáros, P., Nakar, E., Nousek, J.A., O’Brien, P.T., Page, M., Palmer, D.M., Parsons, A.M., Roming, P.W.A., Sakamoto, T., Sarazin, C.L., Schady, P., Stamatikos, M., Woosley, S.E.: A new $\gamma$-ray burst classification scheme from GRB060614. Nature 444(7122), 1044–1046 (2006) arXiv:astro-ph/0610635 [astro-ph]. https://doi.org/10.1038/nature05376
  * (38) MichałowskI, M.J., Xu, D., Stevens, J., Levan, A., Yang, J., Paragi, Z., Kamble, A., Tsai, A.-L., Dannerbauer, H., van der Horst, A.J., Shao, L., Crosby, D., Gentile, G., Stanway, E., Wiersema, K., Fynbo, J.P.U., Tanvir, N.R., Kamphuis, P., Garrett, M., Bartczak, P.: The second-closest gamma-ray burst: sub-luminous GRB 111005A with no supernova in a super-solar metallicity environment. A&A 616, 169 (2018) arXiv:1610.06928 [astro-ph.HE]. https://doi.org/10.1051/0004-6361/201629942
  * (39) Leśniewska, A., Michałowski, M.J., Kamphuis, P., Dziadura, K., Baes, M., Cerón, J.M.C., Gentile, G., Hjorth, J., Hunt, L.K., Jespersen, C.K., Koprowski, M.P., Floc’h, E.L., Miraghaei, H., Guelbenzu, A.N., Oszkiewicz, D., Palazzi, E., Polińska, M., Rasmussen, J., Schady, P., Watson, D.: The Interstellar Medium in the Environment of the Supernova-less Long-duration GRB 111005A. ApJS 259(2), 67 (2022) arXiv:2202.01188 [astro-ph.GA]. https://doi.org/10.3847/1538-4365/ac5022
  * (40) Rossi, A., Piranomonte, S., Savaglio, S., Palazzi, E., Michałowski, M.J., Klose, S., Hunt, L.K., Amati, L., Elliott, J., Greiner, J., Guidorzi, C., Japelj, J., Kann, D.A., Lo Faro, B., Nicuesa Guelbenzu, A., Schulze, S., Vergani, S.D., Arnold, L.A., Covino, S., D’Elia, V., Ferrero, P., Filgas, R., Goldoni, P., Küpcü Yoldaş, A., Le Borgne, D., Pian, E., Schady, P., Stratta, G.: A quiescent galaxy at the position of the long GRB 050219A. A&A 572, 47 (2014) arXiv:1409.0017 [astro-ph.HE]. https://doi.org/10.1051/0004-6361/201423865
  * (41) Fruchter, A.S., Levan, A.J., Strolger, L., Vreeswijk, P.M., Thorsett, S.E., Bersier, D., Burud, I., Castro Cerón, J.M., Castro-Tirado, A.J., Conselice, C., Dahlen, T., Ferguson, H.C., Fynbo, J.P.U., Garnavich, P.M., Gibbons, R.A., Gorosabel, J., Gull, T.R., Hjorth, J., Holland, S.T., Kouveliotou, C., Levay, Z., Livio, M., Metzger, M.R., Nugent, P.E., Petro, L., Pian, E., Rhoads, J.E., Riess, A.G., Sahu, K.C., Smette, A., Tanvir, N.R., Wijers, R.A.M.J., Woosley, S.E.: Long $\gamma$-ray bursts and core-collapse supernovae have different environments. Nature 441(7092), 463–468 (2006) arXiv:astro-ph/0603537 [astro-ph]. https://doi.org/10.1038/nature04787
  * (42) Fragione, G., Kocsis, B., Rasio, F.A., Silk, J.: Repeated Mergers, Mass-gap Black Holes, and Formation of Intermediate-mass Black Holes in Dense Massive Star Clusters. ApJ 927(2), 231 (2022) arXiv:2107.04639 [astro-ph.GA]. https://doi.org/%****␣nature.tex␣Line␣2200␣****10.3847/1538-4357/ac5026
  * (43) Lien, A., Sakamoto, T., Barthelmy, S.D., Baumgartner, W.H., Cannizzo, J.K., Chen, K., Collins, N.R., Cummings, J.R., Gehrels, N., Krimm, H.A., Markwardt, C.B., Palmer, D.M., Stamatikos, M., Troja, E., Ukwatta, T.N.: The Third Swift Burst Alert Telescope Gamma-Ray Burst Catalog. ApJ 829(1), 7 (2016) arXiv:1606.01956 [astro-ph.HE]. https://doi.org/10.3847/0004-637X/829/1/7
  * (44) Clocchiatti, A., Suntzeff, N.B., Covarrubias, R., Candia, P.: The Ultimate Light Curve of SN 1998bw/GRB 980425. AJ 141(5), 163 (2011) arXiv:1106.1695 [astro-ph.HE]. https://doi.org/10.1088/0004-6256/141/5/163
  * (45) Blagorodnova, N., Gezari, S., Hung, T., Kulkarni, S.R., Cenko, S.B., Pasham, D.R., Yan, L., Arcavi, I., Ben-Ami, S., Bue, B.D., Cantwell, T., Cao, Y., Castro-Tirado, A.J., Fender, R., Fremling, C., Gal-Yam, A., Ho, A.Y.Q., Horesh, A., Hosseinzadeh, G., Kasliwal, M.M., Kong, A.K.H., Laher, R.R., Leloudas, G., Lunnan, R., Masci, F.J., Mooley, K., Neill, J.D., Nugent, P., Powell, M., Valeev, A.F., Vreeswijk, P.M., Walters, R., Wozniak, P.: iPTF16fnl: A Faint and Fast Tidal Disruption Event in an E+A Galaxy. ApJ 844(1), 46 (2017) arXiv:1703.00965 [astro-ph.HE]. https://doi.org/10.3847/1538-4357/aa7579
  * (46) Evans, P.A., Beardmore, A.P., Page, K.L., Tyler, L.G., Osborne, J.P., Goad, M.R., O’Brien, P.T., Vetere, L., Racusin, J., Morris, D., Burrows, D.N., Capalbi, M., Perri, M., Gehrels, N., Romano, P.: An online repository of Swift/XRT light curves of $\gamma$-ray bursts. A&A 469(1), 379–385 (2007) arXiv:0704.0128 [astro-ph]. https://doi.org/%****␣nature.tex␣Line␣2325␣****10.1051/0004-6361:20077530
  * (47) Evans, P.A., Beardmore, A.P., Page, K.L., Osborne, J.P., O’Brien, P.T., Willingale, R., Starling, R.L.C., Burrows, D.N., Godet, O., Vetere, L., Racusin, J., Goad, M.R., Wiersema, K., Angelini, L., Capalbi, M., Chincarini, G., Gehrels, N., Kennea, J.A., Margutti, R., Morris, D.C., Mountford, C.J., Pagani, C., Perri, M., Romano, P., Tanvir, N.: Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs. MNRAS 397(3), 1177–1201 (2009) arXiv:0812.3662 [astro-ph]. https://doi.org/10.1111/j.1365-2966.2009.14913.x
  * (48) Nasa High Energy Astrophysics Science Archive Research Center (Heasarc): HEAsoft: Unified Release of FTOOLS and XANADU (2014)
  * (49) Virtanen, P., Gommers, R., Oliphant, T.E., Haberland, M., Reddy, T., Cournapeau, D., Burovski, E., Peterson, P., Weckesser, W., Bright, J., van der Walt, S.J., Brett, M., Wilson, J., Millman, K.J., Mayorov, N., Nelson, A.R.J., Jones, E., Kern, R., Larson, E., Carey, C.J., Polat, İ., Feng, Y., Moore, E.W., VanderPlas, J., Laxalde, D., Perktold, J., Cimrman, R., Henriksen, I., Quintero, E.A., Harris, C.R., Archibald, A.M., Ribeiro, A.H., Pedregosa, F., van Mulbregt, P., SciPy 1.0 Contributors: SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python. Nature Methods 17, 261–272 (2020). https://doi.org/10.1038/s41592-019-0686-2
  * (50) Tonry, J., Davis, M.: A survey of galaxy redshifts. I. Data reduction techniques. AJ 84, 1511–1525 (1979). https://doi.org/10.1086/112569
  * (51) Barthelmy, S.D., Chincarini, G., Burrows, D.N., Gehrels, N., Covino, S., Moretti, A., Romano, P., O’Brien, P.T., Sarazin, C.L., Kouveliotou, C., Goad, M., Vaughan, S., Tagliaferri, G., Zhang, B., Antonelli, L.A., Campana, S., Cummings, J.R., D’Avanzo, P., Davies, M.B., Giommi, P., Grupe, D., Kaneko, Y., Kennea, J.A., King, A., Kobayashi, S., Melandri, A., Meszaros, P., Nousek, J.A., Patel, S., Sakamoto, T., Wijers, R.A.M.J.: An origin for short $\gamma$-ray bursts unassociated with current star formation. Nature 438(7070), 994–996 (2005) arXiv:astro-ph/0511579 [astro-ph]. https://doi.org/10.1038/nature04392
  * (52) Wilms, J., Allen, A., McCray, R.: On the Absorption of X-Rays in the Interstellar Medium. ApJ 542(2), 914–924 (2000) arXiv:astro-ph/0008425 [astro-ph]. https://doi.org/%****␣nature.tex␣Line␣2500␣****10.1086/317016
  * (53) Willingale, R., Starling, R.L.C., Beardmore, A.P., Tanvir, N.R., O’Brien, P.T.: Calibration of X-ray absorption in our Galaxy. MNRAS 431(1), 394–404 (2013) arXiv:1303.0843 [astro-ph.HE]. https://doi.org/10.1093/mnras/stt175
  * (54) Alard, C., Lupton, R.H.: A Method for Optimal Image Subtraction. ApJ 503(1), 325–331 (1998) arXiv:astro-ph/9712287 [astro-ph]. https://doi.org/10.1086/305984
  * (55) Bloom, J.S., Kulkarni, S.R., Djorgovski, S.G.: The Observed Offset Distribution of Gamma-Ray Bursts from Their Host Galaxies: A Robust Clue to the Nature of the Progenitors. AJ 123(3), 1111–1148 (2002) arXiv:astro-ph/0010176 [astro-ph]. https://doi.org/10.1086/338893
  * (56) Evans, P.A., Beardmore, A.P., Page, K.L., Osborne, J.P., O’Brien, P.T., Willingale, R., Starling, R.L.C., Burrows, D.N., Godet, O., Vetere, L., Racusin, J., Goad, M.R., Wiersema, K., Angelini, L., Capalbi, M., Chincarini, G., Gehrels, N., Kennea, J.A., Margutti, R., Morris, D.C., Mountford, C.J., Pagani, C., Perri, M., Romano, P., Tanvir, N.: Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs. MNRAS 397(3), 1177–1201 (2009) arXiv:0812.3662 [astro-ph]. https://doi.org/10.1111/j.1365-2966.2009.14913.x
  * (57) Schulze, S., Malesani, D., Cucchiara, A., Tanvir, N.R., Krühler, T., de Ugarte Postigo, A., Leloudas, G., Lyman, J., Bersier, D., Wiersema, K., Perley, D.A., Schady, P., Gorosabel, J., Anderson, J.P., Castro-Tirado, A.J., Cenko, S.B., De Cia, A., Ellerbroek, L.E., Fynbo, J.P.U., Greiner, J., Hjorth, J., Kann, D.A., Kaper, L., Klose, S., Levan, A.J., Martín, S., O’Brien, P.T., Page, K.L., Pignata, G., Rapaport, S., Sánchez-Ramírez, R., Sollerman, J., Smith, I.A., Sparre, M., Thöne, C.C., Watson, D.J., Xu, D., Bauer, F.E., Bayliss, M., Björnsson, G., Bremer, M., Cano, Z., Covino, S., D’Elia, V., Frail, D.A., Geier, S., Goldoni, P., Hartoog, O.E., Jakobsson, P., Korhonen, H., Lee, K.Y., Milvang-Jensen, B., Nardini, M., Nicuesa Guelbenzu, A., Oguri, M., Pandey, S.B., Petitpas, G., Rossi, A., Sandberg, A., Schmidl, S., Tagliaferri, G., Tilanus, R.P.J., Winters, J.M., Wright, D., Wuyts, E.: GRB 120422A/SN 2012bz: Bridging the gap between low- and high-luminosity gamma-ray bursts. A&A 566, 102 (2014) arXiv:1401.3774 [astro-ph.HE]. https://doi.org/10.1051/0004-6361/201423387
  * (58) Gompertz, B.P., Levan, A.J., Tanvir, N.R.: A Search for Neutron Star-Black Hole Binary Mergers in the Short Gamma-Ray Burst Population. ApJ 895(1), 58 (2020) arXiv:2001.08706 [astro-ph.HE]. https://doi.org/10.3847/1538-4357/ab8d24
  * (59) D’Ai, A., Melandri, A., D’Avanzo, P., Gropp, J.D., Tohuvavohu, A., Kennea, J.A., Evans, P.A., Osborne, J.P., Page, K.L., Simpson, K.K., Swift-XRT Team: GRB 191019A: Swift-XRT refined Analysis. GRB Coordinates Network 26045, 1 (2019)
  * (60) Conselice, C.J.: The Relationship between Stellar Light Distributions of Galaxies and Their Formation Histories. ApJS 147(1), 1–28 (2003) arXiv:astro-ph/0303065 [astro-ph]. https://doi.org/10.1086/375001
  * (61) Leja, J., Johnson, B.D., Conroy, C., van Dokkum, P.G., Byler, N.: Deriving Physical Properties from Broadband Photometry with Prospector: Description of the Model and a Demonstration of its Accuracy Using 129 Galaxies in the Local Universe. ApJ 837(2), 170 (2017) arXiv:1609.09073 [astro-ph.GA]. https://doi.org/%****␣nature.tex␣Line␣2750␣****10.3847/1538-4357/aa5ffe
  * (62) Johnson, B.D., Leja, J., Conroy, C., Speagle, J.S.: Stellar Population Inference with Prospector. ApJS 254(2), 22 (2021) arXiv:2012.01426 [astro-ph.GA]. https://doi.org/10.3847/1538-4365/abef67
  * (63) Speagle, J.S.: dynesty: A Dynamic Nested Sampling Package for Estimating Bayesian Posteriors and Evidences. MNRAS (2020) arXiv:1904.02180 [astro-ph.IM]. https://doi.org/10.1093/mnras/staa278
  * (64) Conroy, C., Gunn, J.E., White, M.: The Propagation of Uncertainties in Stellar Population Synthesis Modeling. I. The Relevance of Uncertain Aspects of Stellar Evolution and the Initial Mass Function to the Derived Physical Properties of Galaxies. ApJ 699(1), 486–506 (2009) arXiv:0809.4261 [astro-ph]. https://doi.org/10.1088/0004-637X/699/1/486
  * (65) Conroy, C., Gunn, J.E.: The Propagation of Uncertainties in Stellar Population Synthesis Modeling. III. Model Calibration, Comparison, and Evaluation. ApJ 712(2), 833–857 (2010) arXiv:0911.3151 [astro-ph.CO]. https://doi.org/10.1088/0004-637X/712/2/833
  * (66) Cardelli, J.A., Clayton, G.C., Mathis, J.S.: The Relationship between Infrared, Optical, and Ultraviolet Extinction. ApJ 345, 245 (1989). https://doi.org/10.1086/167900
  * (67) Chabrier, G.: Galactic Stellar and Substellar Initial Mass Function. PASP 115(809), 763–795 (2003) arXiv:astro-ph/0304382 [astro-ph]. https://doi.org/10.1086/376392
  * (68) Gallazzi, A., Charlot, S., Brinchmann, J., White, S.D.M., Tremonti, C.A.: The ages and metallicities of galaxies in the local universe. MNRAS 362(1), 41–58 (2005) arXiv:astro-ph/0506539 [astro-ph]. https://doi.org/10.1111/j.1365-2966.2005.09321.x
  * (69) Price, S.H., Kriek, M., Brammer, G.B., Conroy, C., Förster Schreiber, N.M., Franx, M., Fumagalli, M., Lundgren, B., Momcheva, I., Nelson, E.J., Skelton, R.E., van Dokkum, P.G., Whitaker, K.E., Wuyts, S.: Direct Measurements of Dust Attenuation in z ~1.5 Star-forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates. ApJ 788(1), 86 (2014) arXiv:1310.4177 [astro-ph.CO]. https://doi.org/10.1088/0004-637X/788/1/86
  * (70) Leja, J., Johnson, B.D., Conroy, C., van Dokkum, P., Speagle, J.S., Brammer, G., Momcheva, I., Skelton, R., Whitaker, K.E., Franx, M., Nelson, E.J.: An Older, More Quiescent Universe from Panchromatic SED Fitting of the 3D-HST Survey. ApJ 877(2), 140 (2019) arXiv:1812.05608 [astro-ph.GA]. https://doi.org/10.3847/1538-4357/ab1d5a
  * (71) Calzetti, D., Armus, L., Bohlin, R.C., Kinney, A.L., Koornneef, J., Storchi-Bergmann, T.: The Dust Content and Opacity of Actively Star-forming Galaxies. ApJ 533(2), 682–695 (2000) arXiv:astro-ph/9911459 [astro-ph]. https://doi.org/10.1086/308692
  * (72) Cappellari, M.: Full spectrum fitting with photometry in ppxf: non-parametric star formation history, metallicity and the quenching boundary from 3200 LEGA-C galaxies at redshift $z\approx 0.8$. MNRAS submitted (2022) 2208.14974. https://doi.org/10.48550/arXiv.2208.14974
  * (73) Inkenhaag, A., Jonker, P.G., Cannizzaro, G., Mata Sánchez, D., Saxton, R.D.: Host galaxy line diagnostics for the candidate tidal disruption events XMMSL1 J111527.3+180638 and PTF09axc. MNRAS 507(4), 6196–6204 (2021) arXiv:2109.01092 [astro-ph.HE]. https://doi.org/10.1093/mnras/stab2541
  * (74) Perley, D.A., Levan, A.J., Tanvir, N.R., Cenko, S.B., Bloom, J.S., Hjorth, J., Krühler, T., Filippenko, A.V., Fruchter, A., Fynbo, J.P.U., Jakobsson, P., Kalirai, J., Milvang-Jensen, B., Morgan, A.N., Prochaska, J.X., Silverman, J.M.: A Population of Massive, Luminous Galaxies Hosting Heavily Dust-obscured Gamma-Ray Bursts: Implications for the Use of GRBs as Tracers of Cosmic Star Formation. ApJ 778(2), 128 (2013) arXiv:1301.5903 [astro-ph.CO]. https://doi.org/10.1088/0004-637X/778/2/128
  * (75) Nugent, A.E., Fong, W.-f., Dong, Y., Leja, J., Berger, E., Zevin, M., Chornock, R., Cobb, B.E., Kelley, L.Z., Kilpatrick, C.D., Levan, A., Margutti, R., Paterson, K., Perley, D., Rouco Escorial, A., Smith, N., Tanvir, N.: Short GRB Host Galaxies II: A Legacy Sample of Redshifts, Stellar Population Properties, and Implications for their Neutron Star Merger Origins. arXiv e-prints, 2206–01764 (2022) arXiv:2206.01764 [astro-ph.GA]
  * (76) French, K.D., Arcavi, I., Zabludoff, A.I., Stone, N., Hiramatsu, D., van Velzen, S., McCully, C., Jiang, N.: The Structure of Tidal Disruption Event Host Galaxies on Scales of Tens to Thousands of Parsecs. ApJ 891(1), 93 (2020) arXiv:2002.02498 [astro-ph.HE]. https://doi.org/10.3847/1538-4357/ab7450
  * (77) Della Valle, M., Chincarini, G., Panagia, N., Tagliaferri, G., Malesani, D., Testa, V., Fugazza, D., Campana, S., Covino, S., Mangano, V., Antonelli, L.A., D’Avanzo, P., Hurley, K., Mirabel, I.F., Pellizza, L.J., Piranomonte, S., Stella, L.: An enigmatic long-lasting $\gamma$-ray burst not accompanied by a bright supernova. Nature 444(7122), 1050–1052 (2006) arXiv:astro-ph/0608322 [astro-ph]. https://doi.org/10.1038/nature05374
  * (78) Portegies Zwart, S.F., Baumgardt, H., Hut, P., Makino, J., McMillan, S.L.W.: Formation of massive black holes through runaway collisions in dense young star clusters. Nature 428(6984), 724–726 (2004) arXiv:astro-ph/0402622 [astro-ph]. https://doi.org/10.1038/nature02448
  * (79) Bloom, J.S., Giannios, D., Metzger, B.D., Cenko, S.B., Perley, D.A., Butler, N.R., Tanvir, N.R., Levan, A.J., O’Brien, P.T., Strubbe, L.E., De Colle, F., Ramirez-Ruiz, E., Lee, W.H., Nayakshin, S., Quataert, E., King, A.R., Cucchiara, A., Guillochon, J., Bower, G.C., Fruchter, A.S., Morgan, A.N., van der Horst, A.J.: A Possible Relativistic Jetted Outburst from a Massive Black Hole Fed by a Tidally Disrupted Star. Science 333, 203 (2011) arXiv:1104.3257 [astro-ph.HE]. https://doi.org/10.1126/science.1207150
  * (80) Burrows, D.N., Kennea, J.A., Ghisellini, G., Mangano, V., Zhang, B., Page, K.L., Eracleous, M., Romano, P., Sakamoto, T., Falcone, A.D., Osborne, J.P., Campana, S., Beardmore, A.P., Breeveld, A.A., Chester, M.M., Corbet, R., Covino, S., Cummings, J.R., D’Avanzo, P., D’Elia, V., Esposito, P., Evans, P.A., Fugazza, D., Gelbord, J.M., Hiroi, K., Holland, S.T., Huang, K.Y., Im, M., Israel, G., Jeon, Y., Jeon, Y.-B., Jun, H.D., Kawai, N., Kim, J.H., Krimm, H.A., Marshall, F.E., P. Mészáros, Negoro, H., Omodei, N., Park, W.-K., Perkins, J.S., Sugizaki, M., Sung, H.-I., Tagliaferri, G., Troja, E., Ueda, Y., Urata, Y., Usui, R., Antonelli, L.A., Barthelmy, S.D., Cusumano, G., Giommi, P., Melandri, A., Perri, M., Racusin, J.L., Sbarufatti, B., Siegel, M.H., Gehrels, N.: Relativistic jet activity from the tidal disruption of a star by a massive black hole. Nature 476, 421–424 (2011) arXiv:1104.4787 [astro-ph.HE]. https://doi.org/%****␣nature.tex␣Line␣3225␣****10.1038/nature10374
  * (81) Levan, A.J., Tanvir, N.R., Cenko, S.B., Perley, D.A., Wiersema, K., Bloom, J.S., Fruchter, A.S., Postigo, A.d.U., O’Brien, P.T., Butler, N., van der Horst, A.J., Leloudas, G., Morgan, A.N., Misra, K., Bower, G.C., Farihi, J., Tunnicliffe, R.L., Modjaz, M., Silverman, J.M., Hjorth, J., Thöne, C., Cucchiara, A., Cerón, J.M.C., Castro-Tirado, A.J., Arnold, J.A., Bremer, M., Brodie, J.P., Carroll, T., Cooper, M.C., Curran, P.A., Cutri, R.M., Ehle, J., Forbes, D., Fynbo, J., Gorosabel, J., Graham, J., Hoffman, D.I., Guziy, S., Jakobsson, P., Kamble, A., Kerr, T., Kasliwal, M.M., Kouveliotou, C., Kocevski, D., Law, N.M., Nugent, P.E., Ofek, E.O., Poznanski, D., Quimby, R.M., Rol, E., Romanowsky, A.J., Sánchez-Ramírez, R., Schulze, S., Singh, N., van Spaandonk, L., Starling, R.L.C., Strom, R.G., Tello, J.C., Vaduvescu, O., Wheatley, P.J., Wijers, R.A.M.J., Winters, J.M., Xu, D.: An Extremely Luminous Panchromatic Outburst from the Nucleus of a Distant Galaxy. Science 333, 199 (2011) arXiv:1104.3356 [astro-ph.HE]. https://doi.org/10.1126/science.1207143
  * (82) Cenko, S.B., Krimm, H.A., Horesh, A., Rau, A., Frail, D.A., Kennea, J.A., Levan, A.J., Holland, S.T., Butler, N.R., Quimby, R.M., Bloom, J.S., Filippenko, A.V., Gal-Yam, A., Greiner, J., Kulkarni, S.R., Ofek, E.O., Olivares E., F., Schady, P., Silverman, J.M., Tanvir, N.R., Xu, D.: Swift J2058.4+0516: Discovery of a Possible Second Relativistic Tidal Disruption Flare? ApJ 753, 77 (2012) arXiv:1107.5307 [astro-ph.HE]. https://doi.org/10.1088/0004-637X/753/1/77
  * (83) Brown, G.C., Levan, A.J., Stanway, E.R., Tanvir, N.R., Cenko, S.B., Berger, E., Chornock, R., Cucchiaria, A.: Swift J1112.2-8238: a candidate relativistic tidal disruption flare. MNRAS 452, 4297–4306 (2015) arXiv:1507.03582 [astro-ph.HE]. https://doi.org/10.1093/mnras/stv1520
  * (84) Auchettl, K., Guillochon, J., Ramirez-Ruiz, E.: New Physical Insights about Tidal Disruption Events from a Comprehensive Observational Inventory at X-Ray Wavelengths. ApJ 838(2), 149 (2017) arXiv:1611.02291 [astro-ph.HE]. https://doi.org/10.3847/1538-4357/aa633b
  * (85) Saxton, R., Komossa, S., Auchettl, K., Jonker, P.G.: X-Ray Properties of TDEs. Space Sci. Rev. 216(5), 85 (2020). https://doi.org/10.1007/s11214-020-00708-4
  * (86) Maguire, K., Eracleous, M., Jonker, P.G., MacLeod, M., Rosswog, S.: Tidal Disruptions of White Dwarfs: Theoretical Models and Observational Prospects. Space Sci. Rev. 216(3), 39 (2020) arXiv:2004.00146 [astro-ph.HE]. https://doi.org/10.1007/s11214-020-00661-2
  * (87) Levan, A.J., Tanvir, N.R., Starling, R.L.C., Wiersema, K., Page, K.L., Perley, D.A., Schulze, S., Wynn, G.A., Chornock, R., Hjorth, J., Cenko, S.B., Fruchter, A.S., O’Brien, P.T., Brown, G.C., Tunnicliffe, R.L., Malesani, D., Jakobsson, P., Watson, D., Berger, E., Bersier, D., Cobb, B.E., Covino, S., Cucchiara, A., de Ugarte Postigo, A., Fox, D.B., Gal-Yam, A., Goldoni, P., Gorosabel, J., Kaper, L., Krühler, T., Karjalainen, R., Osborne, J.P., Pian, E., Sánchez-Ramírez, R., Schmidt, B., Skillen, I., Tagliaferri, G., Thöne, C., Vaduvescu, O., Wijers, R.A.M.J., Zauderer, B.A.: A New Population of Ultra-long Duration Gamma-Ray Bursts. ApJ 781, 13 (2014) arXiv:1302.2352 [astro-ph.HE]. https://doi.org/10.1088/0004-637X/781/1/13
  * (88) MacLeod, M., Goldstein, J., Ramirez-Ruiz, E., Guillochon, J., Samsing, J.: Illuminating Massive Black Holes with White Dwarfs: Orbital Dynamics and High-energy Transients from Tidal Interactions. ApJ 794(1), 9 (2014) arXiv:1405.1426 [astro-ph.HE]. https://doi.org/10.1088/0004-637X/794/1/9
  * (89) MacLeod, M., Guillochon, J., Ramirez-Ruiz, E., Kasen, D., Rosswog, S.: Optical Thermonuclear Transients from Tidal Compression of White Dwarfs as Tracers of the Low End of the Massive Black Hole Mass Function. ApJ 819(1), 3 (2016) arXiv:1508.02399 [astro-ph.HE]. https://doi.org/10.3847/0004-637X/819/1/3
  * (90) Perets, H.B., Li, Z., Lombardi, J. James C., Milcarek, J. Stephen R.: Micro-tidal Disruption Events by Stellar Compact Objects and the Production of Ultra-long GRBs. ApJ 823(2), 113 (2016) arXiv:1602.07698 [astro-ph.HE]. https://doi.org/10.3847/0004-637X/823/2/113
  * (91) Norris, J.P., Bonnell, J.T.: Short Gamma-Ray Bursts with Extended Emission. ApJ 643(1), 266–275 (2006) arXiv:astro-ph/0601190 [astro-ph]. https://doi.org/10.1086/502796
  * (92) Xue, Y.Q., Zheng, X.C., Li, Y., Brandt, W.N., Zhang, B., Luo, B., Zhang, B.-B., Bauer, F.E., Sun, H., Lehmer, B.D., Wu, X.-F., Yang, G., Kong, X., Li, J.Y., Sun, M.Y., Wang, J.-X., Vito, F.: A magnetar-powered X-ray transient as the aftermath of a binary neutron-star merger. Nature 568(7751), 198–201 (2019) arXiv:1904.05368 [astro-ph.HE]. https://doi.org/10.1038/s41586-019-1079-5
  * (93) Quirola-Vásquez, J., Bauer, F.E., Jonker, P.G., Brandt, W.N., Yang, G., Levan, A.J., Xue, Y.Q., Eappachen, D., Zheng, X.C., Luo, B.: Extragalactic fast X-ray transient candidates discovered by Chandra (2000-2014). A&A 663, 168 (2022) arXiv:2201.07773 [astro-ph.HE]. https://doi.org/10.1051/0004-6361/202243047
  * (94) Heggie, D., Hut, P.: The Gravitational Million-Body Problem: A Multidisciplinary Approach to Star Cluster Dynamics, (2003)
  * (95) Hoang, B.-M., Naoz, S., Kocsis, B., Rasio, F.A., Dosopoulou, F.: Black Hole Mergers in Galactic Nuclei Induced by the Eccentric Kozai-Lidov Effect. ApJ 856(2), 140 (2018) arXiv:1706.09896 [astro-ph.HE]. https://doi.org/10.3847/1538-4357/aaafce
  * (96) Graham, M.J., Ford, K.E.S., McKernan, B., Ross, N.P., Stern, D., Burdge, K., Coughlin, M., Djorgovski, S.G., Drake, A.J., Duev, D., Kasliwal, M., Mahabal, A.A., van Velzen, S., Belecki, J., Bellm, E.C., Burruss, R., Cenko, S.B., Cunningham, V., Helou, G., Kulkarni, S.R., Masci, F.J., Prince, T., Reiley, D., Rodriguez, H., Rusholme, B., Smith, R.M., Soumagnac, M.T.: Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational-Wave Event S190521g∗. Phys. Rev. Lett. 124(25), 251102 (2020) arXiv:2006.14122 [astro-ph.HE]. https://doi.org/10.1103/PhysRevLett.124.251102
  * (97) Graham, M.J., McKernan, B., Ford, K.E.S., Stern, D., Djorgovski, S.G., Coughlin, M., Burdge, K.B., Bellm, E.C., Helou, G., Mahabal, A.A., Masci, F.J., Purdum, J., Rosnet, P., Rusholme, B.: A light in the dark: searching for electromagnetic counterparts to black hole-black hole mergers in LIGO/Virgo O3 with the Zwicky Transient Facility. arXiv e-prints, 2209–13004 (2022) arXiv:2209.13004 [astro-ph.HE]
  * (98) Mandel, I., Broekgaarden, F.S.: Rates of compact object coalescences. Living Reviews in Relativity 25(1), 1 (2022) arXiv:2107.14239 [astro-ph.HE]. https://doi.org/10.1007/s41114-021-00034-3
  * (99) Belczynski, K., Perna, R., Bulik, T., Kalogera, V., Ivanova, N., Lamb, D.Q.: A Study of Compact Object Mergers as Short Gamma-Ray Burst Progenitors. ApJ 648(2), 1110–1116 (2006) arXiv:astro-ph/0601458 [astro-ph]. https://doi.org/10.1086/505169
  * (100) Wiggins, B.K., Fryer, C.L., Smidt, J.M., Hartmann, D., Lloyd-Ronning, N., Belcynski, C.: The Location and Environments of Neutron Star Mergers in an Evolving Universe. ApJ 865(1), 27 (2018) arXiv:1807.02853 [astro-ph.HE]. https://doi.org/10.3847/1538-4357/aad2d4
  * (101) Chambers, K.C., Magnier, E.A., Metcalfe, N., Flewelling, H.A., Huber, M.E., Waters, C.Z., Denneau, L., Draper, P.W., Farrow, D., Finkbeiner, D.P., Holmberg, C., Koppenhoefer, J., Price, P.A., Rest, A., Saglia, R.P., Schlafly, E.F., Smartt, S.J., Sweeney, W., Wainscoat, R.J., Burgett, W.S., Chastel, S., Grav, T., Heasley, J.N., Hodapp, K.W., Jedicke, R., Kaiser, N., Kudritzki, R.-P., Luppino, G.A., Lupton, R.H., Monet, D.G., Morgan, J.S., Onaka, P.M., Shiao, B., Stubbs, C.W., Tonry, J.L., White, R., Bañados, E., Bell, E.F., Bender, R., Bernard, E.J., Boegner, M., Boffi, F., Botticella, M.T., Calamida, A., Casertano, S., Chen, W.-P., Chen, X., Cole, S., Deacon, N., Frenk, C., Fitzsimmons, A., Gezari, S., Gibbs, V., Goessl, C., Goggia, T., Gourgue, R., Goldman, B., Grant, P., Grebel, E.K., Hambly, N.C., Hasinger, G., Heavens, A.F., Heckman, T.M., Henderson, R., Henning, T., Holman, M., Hopp, U., Ip, W.-H., Isani, S., Jackson, M., Keyes, C.D., Koekemoer, A.M., Kotak, R., Le, D., Liska, D., Long, K.S., Lucey, J.R., Liu, M., Martin, N.F., Masci, G., McLean, B., Mindel, E., Misra, P., Morganson, E., Murphy, D.N.A., Obaika, A., Narayan, G., Nieto-Santisteban, M.A., Norberg, P., Peacock, J.A., Pier, E.A., Postman, M., Primak, N., Rae, C., Rai, A., Riess, A., Riffeser, A., Rix, H.W., Röser, S., Russel, R., Rutz, L., Schilbach, E., Schultz, A.S.B., Scolnic, D., Strolger, L., Szalay, A., Seitz, S., Small, E., Smith, K.W., Soderblom, D.R., Taylor, P., Thomson, R., Taylor, A.N., Thakar, A.R., Thiel, J., Thilker, D., Unger, D., Urata, Y., Valenti, J., Wagner, J., Walder, T., Walter, F., Watters, S.P., Werner, S., Wood-Vasey, W.M., Wyse, R.: The Pan-STARRS1 Surveys. arXiv e-prints, 1612–05560 (2016) arXiv:1612.05560 [astro-ph.IM]
  * (102) McMahon, R.G., Banerji, M., Gonzalez, E., Koposov, S.E., Bejar, V.J., Lodieu, N., Rebolo, R., VHS Collaboration: First Scientific Results from the VISTA Hemisphere Survey (VHS). The Messenger 154, 35–37 (2013)
  * (103) Wright, E.L., Eisenhardt, P.R.M., Mainzer, A.K., Ressler, M.E., Cutri, R.M., Jarrett, T., Kirkpatrick, J.D., Padgett, D., McMillan, R.S., Skrutskie, M., Stanford, S.A., Cohen, M., Walker, R.G., Mather, J.C., Leisawitz, D., Gautier, I. Thomas N., McLean, I., Benford, D., Lonsdale, C.J., Blain, A., Mendez, B., Irace, W.R., Duval, V., Liu, F., Royer, D., Heinrichsen, I., Howard, J., Shannon, M., Kendall, M., Walsh, A.L., Larsen, M., Cardon, J.G., Schick, S., Schwalm, M., Abid, M., Fabinsky, B., Naes, L., Tsai, C.-W.: The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance. AJ 140(6), 1868–1881 (2010) arXiv:1008.0031 [astro-ph.IM]. https://doi.org/10.1088/0004-6256/140/6/1868