11institutetext: INAF - Osservatorio Astronomico di Brera, Via Brera 28,
20121, Milano, Italy & Via Bianchi 46, Merate (LC), Italy 22institutetext:
Department of Physics, Institute for Astrophysics and Computational Sciences,
The Catholic University of America, Washington, DC, 20064, USA
33institutetext: Dipartimento di Fisica, Università degli Studi di Roma “Tor
Vergata”, Via della Ricerca Scientifica 1, 00133, Roma, Italy 44institutetext:
X-ray Astrophysics Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD
20771, USA 55institutetext: Department of Astronomy, University of Maryland,
College Park, MD 20742, USA 66institutetext: INAF – Osservatorio Astronomico
di Roma, Via Frascati 33, 00044 Monte Porzio Catone, Roma, Italy
77institutetext: Dipartimento di Fisica, Università degli Studi di Milano, Via
Celoria, 16, 20133 Milano, Italy 88institutetext: INAF - Istituto di
Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133,
Roma, Italy 99institutetext: INAF, Osservatorio di Astrofisica e Scienza dello
Spazio, via P. Gobetti 93/3, 40129 Bologna, Italy 1010institutetext:
Department of Astrophysical Sciences, Princeton University, Princeton, NJ
08544, USA 1111institutetext: Space Science Data Center, Agenzia Spaziale
Italiana, Via del Politecnico snc, 00133 Roma, Italy 1212institutetext: Núcleo
de Astronomía de la Facultad de Ingeniería, Universitad Diego Portales, Av.
Ejército Libertador 441, Santiago, Chile

# X-ray obscuration from a variable ionized absorber in PG 1114+445

R. Serafinelli<EMAIL_ADDRESS>V. Braito 1122 P. Severgnini 11
F. Tombesi 33445566 G. Giani 1177 E. Piconcelli 66 R. Della Ceca 11
F. Vagnetti 3388 M. Gaspari 991010 F. G. Saturni 661111 R. Middei 661111 A.
Tortosa 1212

(Received XXX; accepted YYY)

Photoionized absorbers of outflowing gas are commonly found in the X-ray
spectra of active galactic nuclei (AGN). While most of these absorbers are
seldom significantly variable, some ionized obscurers have been increasingly
found to substantially change their column density on a wide range of time
scales. These $N_{\text{H}}$ variations are often considered as the signature
of the clumpy nature of the absorbers. Here we present the analysis of a new
Neil Gehrels Swift Observatory campaign of the type-1 quasar PG 1114+445,
which was observed to investigate the time evolution of the multiphase
outflowing absorbers previously detected in its spectra. The analyzed dataset
consists of 22 observations, with a total exposure of $\sim 90$ ks, spanning
about $20$ months. During the whole campaign, we report an unusually low flux
state with respect to all previous X-ray observations of this quasar. From the
analysis of the stacked spectra we find a fully covering absorber with a
column density $\log(N_{\text{H}}/\text{cm}^{-2})=22.9^{+0.3}_{-0.1}$. This is
an order of magnitude higher than the column density measured in the previous
observations. This is either due to a variation of the known absorbers, or by
a new one, eclipsing the X-ray emitting source. We also find a ionization
parameter of $\log(\xi/\text{erg cm s}^{-1})=1.4^{+0.6}_{-0.2}$. Assuming that
the obscuration lasts for the whole duration of the campaign, i.e. more than
$20$ months, we estimate the minimum distance of the ionized clump, which is
located at $r\gtrsim 0.5$ pc.

###### Key Words.:

X-rays: galaxies – galaxies: active – quasars: general – quasars: individual:
PG 1114+445

##  1 Introduction

Observation ID | Date | Exposure (s)
---|---|---
00011004001 | 2019-03-08 | 4909
00011004002 | 2019-03-08 | 4978
00011004003 | 2019-03-15 | 4258
00011004004 | 2019-03-15 | 4475
00011004005 | 2019-03-29 | 4249
00011004006 | 2019-03-30 | 4750
00011004007 | 2019-04-29 | 4957
00011004008 | 2019-04-29 | 4821
00011004009 | 2019-05-06 | 4313
00011004010 | 2019-05-06 | 1920
00011004011 | 2019-05-21 | 5152
00011004012 | 2019-05-21 | 4874
00011004013 | 2019-06-21 | 5070
00011004014 | 2019-06-21 | 5151
00011004015 | 2019-06-28 | 4404
00011004016 | 2019-06-28 | 4849
00011004017 | 2019-07-13 | 4051
00011004018 | 2019-07-13 | 4527
00089058001 | 2020-10-26 | 1804
00011004019 | 2020-12-06 | 1855
00011004020 | 2020-12-08 | 2453
00011004021 | 2020-12-08 | 2795
Table 1: The list of X-ray observations taken by Swift-XRT, with OBSID,
observation date and exposure.

Active galactic nuclei (AGN) are extremely luminous extragalactic objects,
located at the center of their host galaxies, and powered by the accretion of
matter onto a supermassive black hole (SMBH). AGN are now considered a major
player in shaping their host galaxy during its evolution, since many of its
properties are correlated with the mass of the central SMBH (e.g., Ferrarese &
Merritt, 2000; Häring & Rix, 2004; Gaspari et al., 2019). Outflows are one of
the main mechanisms by which the black hole is believed to transport its
energy to large distances (e.g., King & Pounds, 2015; Fiore et al., 2017;
Cicone et al., 2018; Laha et al., 2021). Such winds are commonly found in AGN
spectra, at many wavelengths (e.g., Gibson et al., 2009; Harrison et al.,
2014; Cicone et al., 2014; Vietri et al., 2018).
In the X-ray band, absorption features are the typical signature of the
presence of outflows. Low-ionization absorbers ($\log(\xi/\text{erg cm
s}^{-1})\lesssim 2$), characterized by a low outflow velocity
($v_{\text{out}}\sim 100-1000$ km s-1), are found in about $65\%$ of soft
X-ray ($E\lesssim 2$ keV) spectra of nearby AGN, and they are often known as
warm absorbers (WAs, e.g., Halpern, 1984; Blustin et al., 2005; McKernan et
al., 2007; Laha et al., 2014). More than $30\%$ X-ray-detected AGN show
evidence of the presence of ultra-fast outflows (UFOs, e.g., Chartas et al.,
2002; Pounds et al., 2003b, a; Braito et al., 2007; Tombesi et al., 2010;
Gofford et al., 2013; Tombesi et al., 2015; Nardini et al., 2015; Ballo et
al., 2015). UFOs are extremely ionized ($\log(\xi/\text{erg cm s}^{-1})\sim
3-6$) absorbers, detected as blueshifted absorption lines of Fe XXV and XXVI,
with typical outflow velocity of $v_{\text{out}}\sim 0.1c$, but capable of
reaching near-relativistic values of $\sim 0.5c$ (e.g., Reeves et al., 2018;
Luminari et al., 2021).
While UFOs are extremely variable (e.g., Matzeu et al., 2017), variability of
soft X-ray ionized absorbers is found less frequently. In some cases, some
sources are found in a state with diminished X-ray flux, due to an increase of
the column density of the obscuring medium. The absorbers are sometimes found
to be persistent for about a decade (e.g., NGC 5548, Kaastra et al., 2014). In
other cases, the obscurer has a much shorter variability timescale (e.g.,
Severgnini et al., 2015; Matzeu et al., 2016; Mehdipour et al., 2017; Middei
et al., 2020). In a few other cases, a source was found in an higher flux
state than its usual one, due to a diminished obscuring power of the WA (e.g.,
Braito et al., 2014). All these cases suggest a clumpy structure for the
ionized and possibly outflowing absorbers around the AGN, which is predicted
by duty-cycle theoretical models such as chaotic cold accretion (CCA, e.g.,
Gaspari et al., 2013; Gaspari & Sadowski, 2017). Such clumpy material can be
part of the multiphase rain condensing out of the hot halo, which then
eventually contributes to the feeding component, alongside the feedback
channel. Indeed, both feeding and feedback processes are expected to be
tightly self-regulated over the cosmic time and over nine orders of magnitude
in spatial scale (see e.g., Gaspari et al., 2020, for a review).
The type-1 quasar PG 1114+445 ($z=0.144$, Hewett & Wild, 2010) has an
estimated black hole mass of $\log(M/M_{\odot})\simeq 8.8$ and bolometric
luminosity of $\log(L_{\text{bol}}/\text{erg s}^{-1})\simeq 45.7$ (Shen et
al., 2011). Hence, the source is accreting with an Eddington ratio of
$\log(L_{\text{bol}}/L_{\text{Edd}})\simeq-1.14$. The source is well known to
host multiple absorbers, in both the UV and X-ray bands. An UV observation
taken in 1996 with the Faint Object Spectrograph (FOS) on board of the Hubble
Space Telescope (HST) was able to detect Ly$\alpha$ and C IV absorption lines
in the spectrum of this quasar. For such lines, an outflowing velocity of
$\sim 530$ km s-1 was measured (Mathur et al., 1998). The observation was
simultaneous with an Advance Satellite for Cosmology and Astrophysics (ASCA)
pointing, that highlighted the presence of an ionized WA, and showed marginal
evidence of the presence of an absorption line at $E\sim 7.3$ keV (George et
al., 1997). The UV absorption lines and the X-ray warm absorber have similar
ionizations and therefore they likely trace the same material (Mathur et al.,
1998).
The source was observed again in 2002 with XMM-Newton (Jansen et al., 2001),
revealing that the absorption complex consisted of two WA layers (Ashton et
al., 2004; Piconcelli et al., 2005). A further XMM-Newton campaign of 11
observations was performed in 2010. The data from this campaign, together with
a re-analysis of the 2002 observation (Serafinelli et al., 2019, hereafter
Paper I), found that one of the two absorbers has typical WA parameters – i.e.
column density $N_{\text{H}}\simeq 7.6\times 10^{21}$ cm-2, and ionization
parameter $\log(\xi/\text{erg cm s}^{-1})\simeq 0.35$ with velocity below the
energy resolution – likely associated with the UV absorber (Mathur et al.,
1998). The second absorber shares very similar parameters with the WA
($N_{\text{H}}\sim 3\times 10^{21}$ cm-2 and $\log(\xi/\text{erg cm
s}^{-1})\leavevmode\nobreak\ \sim 0.5$), with the exception of the outflow
velocity, which is high enough to be detected with the EPIC cameras on board
XMM-Newton ($v_{\text{out}}/c=0.12\pm 0.03$). Low-ionization fast outflows
were also found in other sources (e.g., Longinotti et al., 2015; Pounds et
al., 2016; Reeves et al., 2020). In addition, a high-ionization UFO
($v_{\text{out}}/c=0.15\pm 0.04$, consistent with the fast absorber) was found
in three spectra. This evidence led to the interpretation of a UFO pushing and
entraining the host galaxy interstellar medium to a comparable velocity,
producing a so-called entrained ultra-fast outflow (E-UFO, Paper I).
In this paper we analyze the data taken during a recent Neil Gehrels Swift
Observatory (hereafter Swift) X-Ray Telescope (XRT, Gehrels et al., 2004)
campaign, which was proposed to study the possible variability of the
absorbers found in Paper I, on timescales from days to months. In Sect. 2 we
describe how the data was prepared for the analysis. In Sect. 3 we analyze the
X-ray amplitude and spectral variability, while in Sect. 4 we present a
detailed spectroscopy of the source. In Sect. 5 we analyze the variability of
the X-ray/UV ratio. We summarize and discuss our results in Sect. 6.
Throughout the paper, we adopt the following cosmology: $\Omega_{m}=0.3$,
$\Omega_{\Lambda}=0.7$, and $H_{0}=70$ km s-1 Mpc-1. All uncertainties are
reported at a $90\%$ confidence level.

##  2 Observations and data reduction

Figure 1: Swift-XRT count rates in the energy band $E=0.5-10$ keV. The magenta
star represents OBSID 00089058001, that was not part of our campaign.

Figure 2: Left panel. Full-band ($E=0.5-10$ keV) light curve, using ASCA data
(blue triangle), XMM-Newton (red squares), our Swift-XRT campaign (black
circles) and additional archival Swift-XRT observation (magenta star). Right
panel. The time variability of the hardness ratio HR=$(H-S)/(H+S)$, where $S$
and $H$ are the $0.5-2$ and $2-10$ keV count rates, respectively, is shown.
There is a noticeable hardening of the spectrum in the most recent data. The
count rates of the ASCA and EPIC-pn observations were converted into Swift-XRT
count rates following the procedure described in Sect. 3.

The observations were performed during Swift Cycle 15 (PI: Serafinelli) from
March to July $2019$ (OBSID 00011004001 to 00011004018), and then three
additional observations were taken $15$ months later, in December $2020$
(OBSID 00011004019 to 00011004021). The observations were spaced by $7$, $15$
and $30$ days, in order to analyze possible short-time variability within the
campaign. A further archival observation, OBSID 00089058001, not part of our
campaign, taken in October 26th 2020, is also considered here. Most
observations are about $\sim 4-5$ ks long, with some observations being only
$\sim 2$ ks long. The list of Swift-XRT observations is shown in Table 1. The
total exposure time is $\sim 90$ ks.
For each Swift-XRT observation, the source and background spectra were
extracted using the HEASOFT task XSELECT. The source spectrum was extracted
from a circular area of $40"$ radius around the object, while the background
spectrum was extracted from two source-free circular areas of $40"$ radius
each in the proximity of the source. Ancillary files were produced using the
XRTMKARF task, while the response was taken from the HEASOFT CALDB repository.
Each Swift observation provided a UltraViolet and Optical Telescope (UVOT)
pointing, with a single filter, centered on the source. The source
monochromatic flux was measured within circular apertures of $5"$ radius,
while the background was extracted from an annulus region, centered on the
source, with internal radius of $15"$ and external radius of $40"$, using the
UVOTSOURCE task.

##  3 X-ray variability

The Swift-XRT count rate light curve of PG 1114+445 in the $0.5-10$ keV full
band is shown in Fig. 1. The average count rate is $\sim 1.5\times 10^{-2}$
cts s-1. We compare the current data set with archival X-ray pointings from
ASCA, taken in 1996 and XMM-Newton, taken in 2002 and 2010. The products of
the ASCA observation were downloaded from the Tartarus
database111https://heasarc.gsfc.nasa.gov/FTP/asca/data/tartarus/products/74072000/74072000_gsfc.html
(Turner et al., 2001), while details on the XMM-Newton data reduction can be
found in Paper I. In order to compare data taken with different telescopes, we
convert the X-ray count rates into fluxes. All fluxes are obtained with the
web tool WebPIMMS222https://heasarc.gsfc.nasa.gov/cgi-
bin/Tools/w3pimms/w3pimms.pl, adopting a simple AGN X-ray spectrum, composed
by a typical $\Gamma=1.9$ powerlaw (e.g., Corral et al., 2011; Serafinelli et
al., 2017), at the redshift of the source ($z=0.144$), with Galactic
absorption ($N_{\text{H,Gal}}=1.87\times 10^{20}$ cm-2, HI4PI Collaboration et
al., 2016). The full band fluxes as a function of the observation time are
plotted in the left panel of Fig. 2, where an evident decrease of the X-ray
flux can be already identified with a visual inspection.
The possible presence of obscuration can be investigated by the use of the
hardness ratio (HR), which we define as $(H-S)/(H+S)$, where $S$ is the count
rate in the soft band ($E=0.5-2$ keV), and $H$ the count rate in the hard band
($E=2-10$ keV). In order to deal with comparable HR, which are typically
different due to the different response of the instruments, we convert all the
count rates to the ones of Swift-XRT, using WebPIMMS and assuming again a
simple absorbed $\Gamma=1.9$ powerlaw at $z=0.144$, with
$N_{\text{H,Gal}}=1.87\times 10^{20}$ cm-2. As shown in Fig. 2 (right panel),
there is an average hardening of the spectrum in the Swift-XRT observations,
whereas the HR values during the whole Swift-XRT campaign are roughly
consistent within the error bars. During the observation performed on 26th
October 2020, i.e. the magenta point in Figs. 1 and 2 the flux was higher than
during the rest of the 2019-2020 campaign. However, the HR is still consistent
with the value of the other observations of the Swift campaign. The increased
HR with respect to the XMM-Newton observations suggests that the lower flux
state is not due to a change in the primary continuum, but likely to a
variation of the column density of one or more of the known absorbers found in
Paper I.

##  4 X-ray spectral analysis

Figure 3: Composite Swift-XRT spectrum (black), with its best-fit model (upper
panel) and data-to-model ratios (lower panel). For comparison, we also show
the 2002 EPIC-pn observation (blue) and the lowest-flux spectrum of the 2010
campaign (orange). Figure 4: Contour plot for the ionization $\log\xi$ and the
column density $N_{\text{H}}$. The red line represents the $1\sigma$
confidence level ($68\%$), while the green and blue lines represent the
$2\sigma$ ($95\%$) and $3\sigma$ ($99.7\%$) confidence levels. The X marks the
best-fit values.

Given that all Swift-XRT observations have small number of photon counts, in
order to maximize the signal-to-noise ratio we combine all the observations
into a single spectrum using the HEASOFT task ADDSPEC. We bin the combined
spectrum, which consists of $\sim 1300$ net counts, to have at least $10$
counts per energy channel.
All spectral fits are performed using XSPEC v12.10 (Arnaud, 1996), adopting a
C-statistic, given the low number of photons for each bin (e.g., Kaastra,
2017). We first attempt to fit the combined spectrum with a simple model,
consisting in a power-law component and and an emission line, with Galactic
absorption characterized by a fixed column density
$N_{\text{H,Gal}}=1.87\times 10^{20}$ cm-2 (HI4PI Collaboration et al., 2016):
Tbabs $\times$ (powerlaw $+$ zgauss). The fit results in an unacceptable
C-statistic: $C/\text{dof}=229/106$, where dof is the degree of freedom, and
an unrealistic photon index, $\Gamma=0.4\pm 0.1$.
Based on previous analyses of PG 1114+445 (George et al., 1997; Ashton et al.,
2004; Piconcelli et al., 2005, Paper I), we include an ionized absorber, using
a partial covering model, ZXIPCF (Reeves et al., 2008). The assumed model is
therefore Tbabs $\times$ zxipcf $\times$ (powerlaw $+$ zgauss). The addition
of this ionized absorption component significantly improves the goodness of
fit, with a C-stat of $C/\text{dof}=106/103$. The best-fit value found for the
photon index is $\Gamma=1.6^{+0.3}_{-0.4}$, which is consistent with the
values measured in Paper I. We find that the absorber is moderately ionized,
$\log(\xi/\text{erg cm s}^{-1})=1.4_{-0.2}^{+0.6}$, and almost fully covering,
with covering factor $C_{f}=0.96^{+0.03}_{-0.07}$), with a column density of
$N_{\text{H}}=7_{-1}^{+5}\times 10^{22}$ cm-2. Such value is a factor of $\sim
10$ larger than the column density of any low-ionization absorber detected in
Paper I, confirming that the flux decrease is mainly due to a column density
increase with respect to the $2010$ observations. The spectrum, the best-fit
model and the data-to-model residuals are shown in Fig. 3. The confidence
contour plot of the joint errors of the ionization parameter vs $N_{\text{H}}$
is shown in Fig. 4. In particular, the column density is larger than the
$N_{\text{H}}$ of any soft X-ray absorber detected in Paper I at $3\sigma$
confidence level.

Parameter | Value
---|---
$\log N_{\text{H}}$ (cm-2) | $22.9_{-0.1}^{+0.3}$
$\log\xi$ (erg cm s-1) | $1.4_{-0.2}^{+0.6}$
$C_{f}$ | $0.96_{-0.07}^{+0.03}$
$\Gamma$ | $1.6^{+0.3}_{-0.4}$
norm (cts s-1) | $3.1_{-1.4}^{+2.2}\times 10^{-4}$
$E_{\text{K}\alpha}$ (keV) | $6.28\pm 0.08$
norm${}_{\text{K}\alpha}$ (cts s-1) | $7_{-3}^{+4}\times 10^{-6}$
Cstat/dof | $106/103$
Table 2: Summary of best-fit parameters for our best model: TBabs $\times$
zxipcf $\times$ (powerlaw $+$ zgauss). Errors are given at $90\%$ confidence
level.

##  5 UV variability

OBSID | UV Filter | Flux ($10^{-15}$ erg cm-2 s-1 $\AA^{-1}$)
---|---|---
00011004001 | UVM2 | $4.19\pm 0.07$
00011004002 | UVW2 | $5.01\pm 0.07$
00011004003 | UVM2 | $4.39\pm 0.07$
00011004004 | UVW2 | $4.82\pm 0.07$
00011004005 | UVM2 | $4.38\pm 0.07$
00011004006 | UVW2 | $5.18\pm 0.08$
00011004007 | UVM2 | $3.92\pm 0.06$
00011004008 | UVW2 | $4.58\pm 0.07$
00011004009 | UVM2 | $3.92\pm 0.06$
00011004010 | UVW2 | $4.42\pm 0.08$
00011004011 | UVM2 | $3.91\pm 0.06$
00011004012 | UVW2 | $4.39\pm 0.07$
00011004013 | UVM2 | $4.06\pm 0.07$
00011004014 | UVW2 | $4.95\pm 0.07$
00011004015 | UVM2 | $4.35\pm 0.07$
00011004016 | UVW2 | $5.13\pm 0.08$
00011004017 | UVM2 | $4.17\pm 0.07$
00011004018 | UVW2 | $4.96\pm 0.07$
00089058001 | U | $3.68\pm 0.06$
00011004019 | UVW2 | $5.78\pm 0.10$
00011004020 | UVW1 | $4.67\pm 0.08$
00011004021 | U | $3.83\pm 0.06$
Table 3: List of flux densities in units of $10^{-15}$ erg cm-2 s-1 $\AA^{-1}$
for each Swift-UVOT pointing. The corresponding UVOT filter is also reported.
Figure 5: Plot of the $\alpha_{\text{ox}}$ index versus the UV luminosity,
using unabsorbed X-ray luminosities. The grey points are the quasars analyzed
in Chiaraluce et al. (2018), with the linear best-fit shown as a solid line.
The dashed line is the X-ray weak limit defined by Pu et al. (2020). The red
squares correspond to the XMM-Newton observations, while the black points
correspond to those performed by Swift.

The UV observations are provided by the XMM-Newton Optical Monitor (OM) and by
Swift-UVOT. The OM data were retrieved from the XMM Serendipitous Ultraviolet
Source Survey (XMM-SUSS, Page et al., 2012). All UVOT filters do not show
evidence of relevant variability between 2010 and 2019-2020 (see Table 3).
We computed the X-ray/UV ratio $\alpha_{\text{ox}}$ (e.g., Vignali et al.,
2003; Vagnetti et al., 2010; Lusso & Risaliti, 2016; Chiaraluce et al., 2018),
in order to analyze the relative variability of the X-ray and UV bands, which
is defined as

$\alpha_{\text{ox}}=\frac{\log L(2\text{ keV})-\log
L(2500\,\AA)}{\log\nu(2\text{ keV})-\log\nu(2500\,\AA)},$

where $\nu(2$ keV$)$ and $\nu(2500\,\AA)$ are the frequencies (in Hz) in the
rest frame, corresponding to an energy of $2$ keV and a wavelength of
$2500\,\AA$, respectively. The $2$ keV luminosity of the XRT observations was
computed using XSPEC. We adopted the best-fit model (see Sect. 4) and froze
every parameter with the exception of the column density $N_{\text{H}}$ of the
absorber and the normalization of the power law. We fit each snapshot with
this model to obtain a best-fit model as accurate as possible, and then we
remove the absorption component and use the LUMIN task between $1.99$ and
$2.01$ keV, from which we derive the intrinsic X-ray luminosity $L(2$ keV$)$.
Since the UVOT observations were performed with a single source-centered
filter, we compute the luminosity at $2500\,\AA$ interpolating a spectral
energy distribution obtained averaging thousands of Sloan Digital Sky Survey
(SDSS) observations (Richards et al., 2006). We conservatively compute
$L(2500\,\AA)$ only for those observations performed with the UVM2 filter,
which is centered at $\sim 2250$ $\AA$, corresponding to a rest-frame
wavelength of $\sim 2510$ $\AA$, and therefore close enough to $2500$ $\AA$.
The fluxes are finally corrected for reddening due to the Galactic extintion
adopting $E(B-V)=0.0264$ (Güver & Özel, 2009).
The result is shown in Fig. 5. The Swift observations lie on the ensemble
trend found by Chiaraluce et al. (2018), which is represented by a solid line.
We note that none of the points lie on the X-ray weak limit (dashed line),
which is set $0.3$ dex below the best-fit line (Pu et al., 2020). This is a
further proof that the low flux state of the source is clearly driven by the
obscuration and not by an intrinsic luminosity change.

##  6 Summary and discussion

Figure 6: Contour plots between the redshift of the absorber in the observer
frame $z_{\text{obs}}$ and the ionization parameter $\log\xi$. The red, green
and blue line represent the $1\sigma$ ($68\%$), $2\sigma$ ($95\%$) and
$3\sigma$ ($99.7\%$) confidence levels, respectively. Figure 7: Time
variability of the absorber parameters $N_{\text{H}}$ (top) and $\xi$
(middle). For all observations prior to 2019, the black points are referred to
the variable E-UFO, while the constant WA is represented by a red dashed line.
In the lower panel, the light curve of soft X-ray ($E=0.5-2$ keV) count rates
is shown, where the XMM rates were converted into Swift-XRT count rates using
WebPIMMS.

In this work, we have presented the analysis of the Swift observations of the
type-1 quasar PG 1114+445, performed $10$ years after the XMM-Newton
observations analyzed in Paper I. The source is found in a strongly reduced
flux state (Fig. 2), which can be ascribed to an absorption increase by an
obscuring material. Indeed, the spectral analysis highlights the presence of
ionized ($\log\xi/\text{erg cm s}^{-1}\sim 1.4$) material, characterized by a
column density $N_{\text{H}}\sim 7\times 10^{22}$ cm-2. No substantial
variations on the unabsorbed X-ray luminosity of the source is found.
In Paper I two absorbers were found in the soft X-rays, a slow and constant WA
with $N_{\text{H}}\sim 7\times 10^{21}$ cm-2, and a mildly-relativistic
absorber, identified with an entrained ultra-fast outflow (E-UFO), with
variable column density with median value $N_{\text{H}}\sim 3\times 10^{21}$
cm-2 and a dispersion of $\sim 6\times 10^{20}$ cm-2. Both these column
densites are a factor of $10$ smaller than the one found in this work. If we
allow for an outflowing velocity of this ionized absorber, we obtain that the
best-fit value of the redshift of the absorber in the observer frame is
$z_{\text{obs}}\sim 0.09$, which corresponds to $v_{\text{out}}\sim 0.05c$.
However, the low statistic of the data set does not allow to successfully
measure both the ionization parameter and the velocity, which are notoriously
affected by degeneracy, as shown by their contour plot in Fig. 6. We note that
lower values of the absorber redshift are allowed at $1\sigma$ confidence
level, down to $z_{\text{obs}}\simeq-0.03$ ($v_{\text{out}}\simeq 0.16c$),
consistent with both the E-UFO and the WA measured in Paper I. In addition,
the ionization parameter can be as low as $\log\xi\lesssim 0.4$ at $3\sigma$
confidence level, consistent with the E-UFO median value of 2010. This
suggests that Swift-XRT is not able to resolve the complex structure of the
absorbers measured in Paper I, but it may be hidden by the dominant absorber
that we observe in this campaign.
We can estimate a lower limit for its distance using the equation by Risaliti
et al. (2002):

$r\simeq 4\times
10^{16}\frac{M_{\text{BH}}}{10^{M}_{\odot}}\left(\frac{n}{10^{9}\text{
cm}^{-3}}\frac{t}{1\text{ day}}\frac{N_{\text{H}}}{5\times 10^{22}\text{
cm}^{-2}}\right)^{2}\text{cm}\\\ $ (1) $\simeq 2\times
10^{23}n_{9}^{2}\;\text{cm,}$

where $M_{\text{BH}}\simeq 6.3\times 10^{8}M_{\odot}$ is the black hole mass,
$n$ is the density of the clump ($n_{9}$ in units of $10^{9}$ cm-3),
$N_{\text{H}}\simeq 7\times 10^{22}$ cm-2 the column density of the clump, and
$t$ is the duration of the obscuration. We assume here that the obscuration
lasts during the whole campaing, including the times between 2019 and 2020
when the source was not observed. Therefore, we adopt $t\gtrsim 560$ days
(rest-frame) as the duration of the obscuration, which is only a lower limit
since it could last beyond the end of the campaign. The density of the clump
can be replaced by inverting the definition of ionization parameter:

$n=\frac{L_{\text{ion}}}{r^{2}\xi},$ (2)

where $L_{\text{ion}}\simeq 1.5\times 10^{44}$ erg s-1 is obtained from the
unabsorbed best-fit model, $\xi=25^{+35}_{-11}$ erg cm s-1 is the best-fit
value (see Table 2). Combining Eq.1 and Eq. 2 we obtain an upper limit for the
density of the obscuring clump $n=(2.7\pm 0.5)\times 10^{6}$ cm-3, which means
that it is located at least at $r=(1.5\pm 0.5)\times
10^{18}\;\text{cm}=(0.50\pm 0.15)\;\text{pc}=(8\pm 2)\times 10^{3}r_{s}$,
where $r_{s}=2GM/c^{2}$ is the Schwarzschild radius. The estimated minimum
size of the clump is therefore $R\simeq N_{\text{H}}/n=(6\pm 2)\times 10^{-3}$
pc.
An estimate of the maximum distance of the cloud from the central source might
be given by noting that the size of the clump cannot be larger than its
distance from the X-ray source. Therefore we assume
$N_{\text{H}}=nR<nr_{\text{max}}$ (e.g., Crenshaw & Kraemer, 2012; Tombesi et
al., 2013). Substituting into the definition of ionization parameter we obtain

$r_{\text{max}}=\frac{L_{\text{ion}}}{N_{\text{H}}\xi}.$ (3)

Assuming again $L_{\text{ion}}\simeq 1.5\times 10^{44}$ erg s-1, and the best-
fit values of $N_{\text{H}}$ and $\xi$ (Table 2), we obtain
$r_{\text{max}}=30^{+40}_{-13}\;\text{pc}=5^{+5}_{-2}\times 10^{5}\;r_{s}$.
The increase of column density is likely due to a new clump of absorbing
material, either due to a superposition of the WA and the E-UFO observed in
Paper I, with an increased column density $N_{\text{H}}$, or an additional
absorber located between the central source and the previously known absorber.
The values of the minimum and maximum distance of the clump found in Eqs. 1
and 3 strongly suggest that the absorbing clumps is located outside the
typical boundaries of the broad line region for a quasar of this luminosity.
Indeed, we estimate a broad line region radius of $R_{\text{BLR}}\simeq 0.07$
pc, considering the luminosity $\log(L_{5100\AA}/\text{erg s}^{-1})\simeq
44.77$ of PG 1114+445 (Shen et al., 2011), once the relation between
$R_{\text{BLR}}$ and $L_{5100\AA}$ derived by Bentz et al. (2009) is assumed.
A comparison between the parameters of the absorber here detected and the ones
measured in Paper I is shown in Fig. 7.
While no strong flux variability is detected between the Swift-XRT
observations, minor variations are present (Figs. 1 and 2) and may be tied to
the observed increased clumpiness. For instance, chaotic cold accretion (CCA)
predicts fractal variations with power spectral density proportional to
$f^{-1}$, where $f$ is the time frequency. In other words, smaller clumps are
expected to contribute to the micro variations observed in the light curves
(e.g., Gaspari et al., 2017). The distance estimate puts the cloud at the meso
scale in the CCA self-regulation framework (Gaspari et al., 2020). This is the
typical transition scale at which CCA clouds become more clustered and collide
frequently, thus generating flickering absorbers along the line of sight,
starting from the X-ray/hot phase and potentially down to the radio/molecular
phase (e.g., Tremblay et al., 2018; Rose et al., 2019).
In the last decade many obscuring variable absorbers were found in the X-ray
spectra of nearby AGN (e.g., Markowitz et al., 2014), with timescales ranging
from decades (e.g., Kaastra et al., 2014) to months or weeks (e.g., Matzeu et
al., 2016; Mehdipour et al., 2017; Middei et al., 2020) and even days (e.g,
Braito et al., 2014; Severgnini et al., 2015). These winds, with velocities
than can be higher than typical WA velocities, are important because they may
carry sufficient kinetic power to contribute to possible AGN feedback on the
host galaxy. It is therefore important to continue monitoring these sources
and possibly several others with current facilities such as Swift or eROSITA
(Merloni et al., 2012), and with future missions such as the enhanced X-ray
Timing and Polarimetry mission (eXTP, Zhang et al., 2019), XRISM/Xtend (e.g.,
Yoneyama et al., 2020) or the Athena Wide Field Imager (WFI, Meidinger et al.,
2015) in order to look for both long-term and transient obscuration from
ionized clumps. In the case of PG 1114+445, given the long-term nature of its
obscuration, a monthly monitoring could help to identify lowest and highest
states, to study them with current X-ray telescopes such as XMM-Newton. In the
future, forthcoming microcalorimeters such as Resolve on board XRISM (XRISM
Science Team, 2020) and Athena/X-IFU (Barret et al., 2016) will be able to
measure the X-ray spectrum with unprecedented energy resolution, letting us
measure the outflow velocity of these obscurers with much higher accuracy,
allowing to observe the full range of absorbers in AGN.

###### Acknowledgements.

We thank the referee for improving the paper with useful comments. We
acknowledge financial contribution from the agreement ASI-INAF n.2017-14-H.0.
EP acknowledges support from PRIN MIUR project ”Black Hole winds and the
Baryon Life Cycle of Galaxies: the stone-guest at the galaxy evolution
supper”, contract n. 2017PH3WAT. MG acknowledges partial support by NASA
Chandra GO8-19104X/GO9-20114X and HST GO-15890.020-A grants. AT acknowledges
the financial support from FONDECYT Postdoctorado for the project n. 3190213.
We acknowledge the use of public data from the Swift data archive. This
research has made use of data and software provided by the High Energy
Astrophysics Science Archive Research Center (HEASARC), which is a service of
the Astrophysics Science Division at NASA/GSFC and the High Energy
Astrophysics Division of the Smithsonian Astrophysical Observatory.

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