# Chandra - BAT

R. Silver  Department of Physics and Astronomy, Clemson University, Kinard Lab
of Physics, Clemson, SC 29634, USA  N. Torres-Albà  Department of Physics and
Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634, USA
X. Zhao  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,
Cambridge, MA 02138, USA  Department of Physics and Astronomy, Clemson
University, Kinard Lab of Physics, Clemson, SC 29634, USA  S. Marchesi  INAF -
Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero
Gobetti, 93/3, 40129, Bologna, Italy  Department of Physics and Astronomy,
Clemson University, Kinard Lab of Physics, Clemson, SC 29634, USA  A. Pizzetti
Department of Physics and Astronomy, Clemson University, Kinard Lab of
Physics, Clemson, SC 29634, USA  M. Ajello  Department of Physics and
Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634, USA
G. Cusumano  INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, Via Ugo
la Malfa, 153, I-90146 Palermo PA, Italy  V. La Parola  INAF-Istituto di
Astrofisica Spaziale e Fisica Cosmica, Via Ugo la Malfa, 153, I-90146 Palermo
PA, Italy  A. Segreto  INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica,
Via Ugo la Malfa, 153, I-90146 Palermo PA, Italy  A. Comastri  INAF -
Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero
Gobetti, 93/3, 40129, Bologna, Italy

#  Chandra Follow-up Observations of Swift-BAT-selected AGNs II

R. Silver  Department of Physics and Astronomy, Clemson University, Kinard Lab
of Physics, Clemson, SC 29634, USA  N. Torres-Albà  Department of Physics and
Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634, USA
X. Zhao  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,
Cambridge, MA 02138, USA  Department of Physics and Astronomy, Clemson
University, Kinard Lab of Physics, Clemson, SC 29634, USA  S. Marchesi  INAF -
Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero
Gobetti, 93/3, 40129, Bologna, Italy  Department of Physics and Astronomy,
Clemson University, Kinard Lab of Physics, Clemson, SC 29634, USA  A. Pizzetti
Department of Physics and Astronomy, Clemson University, Kinard Lab of
Physics, Clemson, SC 29634, USA  M. Ajello  Department of Physics and
Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634, USA
G. Cusumano  INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, Via Ugo
la Malfa, 153, I-90146 Palermo PA, Italy  V. La Parola  INAF-Istituto di
Astrofisica Spaziale e Fisica Cosmica, Via Ugo la Malfa, 153, I-90146 Palermo
PA, Italy  A. Segreto  INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica,
Via Ugo la Malfa, 153, I-90146 Palermo PA, Italy  A. Comastri  INAF -
Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero
Gobetti, 93/3, 40129, Bologna, Italy

###### Abstract

We present the combined Chandra and Swift-BAT spectral analysis of nine low-
redshift ($z\leq 0.10$), candidate heavily obscured active galactic nuclei
(AGN) selected from the Swift-BAT 150-month catalog. We located soft (1$-$10
keV) X-ray counterparts to these BAT sources and joint fit their spectra with
physically motivated models. The spectral analysis in the 1$-$150 keV energy
band determined that all sources are obscured, with a line-of-sight column
density N${}_{H}\geq$ 1022 cm-2 at a 90% confidence level. Four of these
sources show significant obscuration with N${}_{H}\geq$ 1023 cm-2 and two
additional sources are candidate Compton-thick Active Galactic Nuclei (CT-
AGNs) with N${}_{H}\geq$ 1024 cm-2. These two sources, 2MASX J02051994-0233055
and IRAS 11058$-$1131, are the latest addition to the previous 3 CT-AGN
candidates found using our strategy for soft X-ray follow-up of BAT sources.
In here we present the results of our methodology so far, and analyze the
effectiveness of applying different selection criteria to discover CT-AGN in
the local Universe. Our selection criteria has a $\sim$20% success rate of
discovering heavily obscured AGN whose CT nature is confirmed by follow-up
NuSTAR observations. This is much higher than the $\sim$5% found in blind
surveys.

##  1 Introduction

Current models have concluded the Cosmic X-ray Background (CXB), the diffuse
X-ray emission in the 1 to $\sim$200$-$300 keV band, is primarily produced by
accreting supermassive black holes (SMBHs), i.e., active galactic nuclei
(AGNs, Alexander et al., 2003; Gandhi & Fabian, 2003; Gilli et al., 2007;
Treister et al., 2009; Ueda et al., 2014). While the CXB emission below 10 keV
has been almost entirely resolved (Worsley et al., 2005; Hickox & Markevitch,
2006), at $\sim$30 keV (the peak of the CXB, Ajello et al., 2008), only 30% of
the emission is accounted for by current observations (Aird et al., 2015;
Civano et al., 2015; Mullaney et al., 2015; Harrison et al., 2016). It is
expected that a considerable fraction (10-20%) of the CXB is produced by a
numerous population of heavily obscured, the so-called Compton thick (CT-)
AGN, which have intrinsic obscuring hydrogen column densities (NH) $\geq$ 1024
cm-2 (Risaliti et al., 1999; Alexander et al., 2003; Gandhi & Fabian, 2003;
Gilli et al., 2007; Treister et al., 2009; Ueda et al., 2014; Ananna et al.,
2019). However, only 5$-$7% of the hard X-ray detected low-$z$ AGNs are
classified as CT-AGNs (Comastri, 2004; Della Ceca et al., 2008; Burlon et al.,
2011; Ricci et al., 2015; Lanzuisi et al., 2018) which is much lower than
those predicted by population synthesis models that aim to explain the CXB
(30$-$50%; see, e.g., Gilli et al., 2007; Ueda et al., 2014; Ananna et al.,
2019). Currently, there are only $\sim$30-35 NuSTAR-confirmed CT-AGN in the
range $z\leq 0.05$ (Torres-Albà et al., 2021)111See full list at
https://science.clemson.edu/ctagn/ctagn/. The low number severely limits any
science designed to study this population. Detecting new CT-AGN in X-rays is
crucial to advance the field, in order to explain the shape of the CXB, and to
study torus properties via complex models.
The emission from CT-AGNs is heavily suppressed below 10 keV due to the heavy
obscuration of the dusty gas surrounding the SMBH, which makes detecting CT-
AGN in X-rays difficult. Their spectra is dominated by the Compton hump at
$\sim$20$-$40 keV, originating from the intrinsic emission being reflected in
the torus.

Several models developed over the past decade successfully describe the X-ray
emission of AGN reprocessed by the torus material, e.g., pexrav (Magdziarz &
Zdziarski, 1995); MYTorus (Murphy & Yaqoob, 2009; Yaqoob, 2012); BNtorus
(Brightman & Nandra, 2011); ctorus (Liu & Li, 2014); borus02 (Baloković et
al., 2018); UXClumpy (Buchner et al., 2019); XClumpy (Tanimoto et al., 2019).
These models are built adopting different assumptions on the geometrical
distribution of the obscuring material (e.g., homogeneous vs clumpy) or its
chemical composition. The clumpy models are significant because numerous works
have observed variability in the line-of-sight column density, suggesting that
a patchy, non-homogeneous distribution of obscuring material is favored by
observational data (Risaliti et al., 2002; Bianchi et al., 2012; Torricelli-
Ciamponi et al., 2014). However, implementing these models requires high-
quality data in order to break the various degeneracies between parameters. It
is thus necessary to increase our pool X-ray CT-AGN, which let the reflection
component shine through thanks to the suppressed line-of-sight. Previous works
have used high-quality X-ray data to successfully constrain torus parameters
(e.g. Zhao et al., 2020).
Instruments such as the Swift X-Ray Telescope (Swift-XRT) on board the Neil
Gehrels Swift satellite (Gehrels et al., 2004), Chandra, and XMM-Newton,
sensitive in the $\sim$0.3$-$10 keV energy range, can only detect the Compton
hump if the source’s spectrum is largely redshifted ($z>1$). In the local
universe ($z<0.1$), an instrument with sensitivity above 10 keV is necessary
to detect and characterize CT-AGNs (e.g., Marchesi et al., 2017a). The wide-
field (120$\times$90 deg2) Burst Alert Telescope (Barthelmy et al., 2005)
continually observes the whole sky in the 15$-$200 keV band. Swift-BAT is thus
an excellent tool to create a census of the hard X-ray emitting sources in the
local universe. The combination of Swift-BAT and soft X-ray instruments has
previously proved successful in selecting and identifying candidate CT-AGNs
(Burlon et al., 2011; Vasudevan et al., 2013; Ricci et al., 2015; Koss et al.,
2016; Marchesi et al., 2017a, b).
In this work, we perform a joint Chandra–Swift-BAT spectral fitting in the
1.0$-$150 keV band of nine AGN detected by Swift-BAT in 150 months of
observations. The joint analysis of Chandra and Swift-BAT data provides an
ample opportunity to constrain the column density of the obscuring material
surrounding the accreting SMBHs and possibly identify new candidate CT-AGNs.
The aim of this work is therefore to obtain a first estimate of the line-of-
sight column density for these sources, which have never been observed before
in soft X-rays. Thanks to this estimate, obtained via our quick snapshot
Chandra program (PI: Marchesi, see Section 2), we find promising targets to
follow-up with joint NuSTAR and XMM-Newton observations. This program will
allow to obtain new high-quality data of promising CT-AGN candidates to
confirm their nature, which will add to the limited pool of high-quality CT-
AGNs that can be used to constrain torus properties (e.g. Zhao et al., 2020)
and CXB models (e.g. Ananna et al., 2019). The second objective of this work
is to present the results of our program so far, and discuss the efficiency of
the selection criteria we have used to target new CT-AGN in the local
Universe.
In addition, Chandra’s unparalleled spatial resolution ($\sim$0.5$\arcsec$)
allows us to detect X-ray emission extended out to kiloparsec scales. Recent
works have discovered CT-AGN with extended emission in the 3-7 keV band
primarily aligned with the ionization cones, but also present in the
orthogonal direction (the cross-cones; see e.g., Fabbiano et al., 2017, 2018;
Jones et al., 2020; Ma et al., 2020; Jones et al., 2021). The study of the
extended emission in CT-AGN has the power to constrain the duty cycle for the
AGN feedback onto the host galaxy ISM (Ma et al., 2020).

This work is organized as follows: Section 2 describes the selection criteria
used to identify potential CT-AGN candidates and the data reduction process.
Section 3 discusses the models used in our spectral fitting and Section 4
describes the derived results. Section 5 reports the findings on the extended
emission. Section 6 summarizes the conclusions and future work. All errors
reported are at a 90% confidence level. Standard cosmological parameters are
as follows: H0 = 70 km s-1 Mpc-1, q0 = 0.0, and $\Lambda$ = 0.73.

##  2 Selection Criteria and Data Reduction

Since its launch, Swift-BAT has continuously observed the hard X-ray sky. Data
from the first 150 months have been combined into a catalog containing sources
detected with fluxes down to $f\sim$ 3.3$\times$10-12 erg s-1 cm-2 in the
15$-$150 keV band (Segreto et al. in preparation222The 150 month catalog can
be found here: https://science.clemson.edu/ctagn/bat-150-month-catalog/). Due
to its high sensitivity and ability to cover the entire sky, Swift-BAT
provides an excellent tool to study the hard X-ray AGN population in the
nearby Universe.
The Swift-BAT data are processed by the BAT_IMAGER code (Segreto et al.,
2010). This code was developed to analyze data from coded mask instruments and
can perform screening, mosaicking, and source detection. All spectra used in
this work have been background subtracted and were acquired by averaging over
the entire Swift-BAT exposure. The standard BAT spectral redistribution matrix
was
used333https://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/data/swift/bat/index.html.
The sample in this work is selected from the 150 month catalog, which includes
a total of 724 galaxies444We note that blazars were removed and 3% of sources
from the catalog do not have a determined $z$. in the local (z $<$ 0.10, D
$\lesssim$ 400 Mpc) Universe. The first step in our three-step program is to
select previously unobserved sources within these 724 to propose for quick
($\sim 10$ ks) Chandra observations. In order to find promising CT-AGN
candidates, we implement the following criteria:

  * •

We select sources at high Galactic latitude ($\lvert b\rvert>$ 10$\degree$)
without a ROSAT (Voges et al., 1999) counterpart. The emission in the 0.1 $-$
2.4 keV555https://heasarc.gsfc.nasa.gov/docs/rosat/ass.html band, in which
ROSAT is sensitive, is easily suppressed in heavily obscured AGN and the lack
of this counterpart already suggests an expected column density logN${}_{H}>$
23 (Ajello et al., 2008; Koss et al., 2016). The added requirement of high
Galactic latitude ensures that the obscuration responsible for the lack of
ROSAT counterpart is not coming from our own galaxy.

  * •

We only select Seyfert 2 galaxies (Sy2s) or sources classified as galaxies.
The absence of broad lines in Sy2s implies the presence of obscuring material
in our line of sight. This is significant as $\sim$95% of Seyfert 2 galaxies
are obscured with a column density logN${}_{H}>$ 22 (Figure 9, Koss et al.,
2017). Sources optically classified as galaxies are likewise likely to be
potentially obscured AGN. This is because a normal galaxy cannot emit strongly
enough in the $15-150$ keV range to be detected by BAT, and must therefore be
an AGN. Any AGN that is optically not classified as such is likely to be
obscured. We note that our nine sources have optical spectra available and
lack typical AGN features, hence they are likely obscured.

  * •

Finally, this sample is limited to sources in the nearby universe because CT-
AGN are detected at much lower redshifts than the rest of the AGN population
(Burlon et al., 2011). Approximately 90% of the Swift-BAT-detected CT-AGN have
been discovered at $z$ $\leq$ 0.1, while unobscured or Compton-thin AGN can be
found up to z$\sim$0.3 (Ricci et al., 2017).

The above selection criteria have proved capable of discovering heavily
obscured AGN candidates in the past, as described in Marchesi et al. (2017a).
The last nine sources for which we obtained Chandra observing time following
the described criteria are analysed in this work, and listed in Table 1.

All sources were observed with 10 ks by Chandra ACIS-S as a part of the
Chandra general observing Cycles 19 and 21 (Proposal numbers 19700430 and
21700085, P.I. Marchesi666https://cxc.harvard.edu/cgi-
bin/propsearch/prop_details.cgi?pid=5182 777https://cxc.harvard.edu/cgi-
bin/propsearch/prop_details.cgi?pid=5667). The CIAO (Fruscione et al., 2006)
4.12 software was used to reduce the data following standard procedures.
Source and background spectra were extracted utilizing the CIAO specextract
tool. Source spectra were calculated with a 5$\arcsec$ radius, while
background spectra used an annulus with internal radius rin = 6$\arcsec$ and
external radius rout = 15$\arcsec$. Background annuli experienced no
contamination from nearby sources. We applied point-source aperture correction
as a part of the source spectral extraction process. We fit the spectra using
Cstat, given how the low count statistic of our sources does not allow the
minimum 15 cts/bin required to use $\chi^{2}$ statistics (for all except MCG
$+$08-33-046888Even in the case of enough counts per bin, Lanzuisi et al.
(2013) showed that cstat yields more constraining results ($<$ 30% for most
sources) when compared to a $\chi^{2}$ analysis.). To bin the spectra, we
followed Lanzuisi et al. (2013) (Appendix A), which study the optimal binning
to use C-statistic (cstat) as a fitting statistic. They find that fitting is
stable regardless of binning at either 1 or 5 cts/bin, but 5 cts/bin results
in the optimal error determination. Therefore, we adopt this value except in
two cases: ESO 090$-$IG 014 and IRAS 11058$-$1131\. Due to the low net counts
($<$90 cts) of these two sources, 5 cts/bin resulted in the dilution of
visible features, such as the iron line, which affected the fit negatively.
For these two sources, we opted for a 3 cts/bin; the value that is closest to
5 without erasing the iron line.

Table 1: Summary of Sources in Our Sample

Swift-BAT ID | Source Name | R.A. | Decl. | $z$ | Exp. Time | Count Rate | Obs Date | Type
---|---|---|---|---|---|---|---|---
|  | (J2000) | (J2000) |  | (ks) | (1–7 keV) |  |
J0205.2$-$0232 | 2MASX J02051994$-$0233055∗ | 02:05:19.9 |  $-$02:33:05.9 | 0.0283 | 9.9 | 4.40e-2 | 2018 June 11 | Ga
J0402.6$-$2107 | ESO 549$-$50† | 04:02:46.1 |  $-$21:07:08.6 | 0.0252 | 9.9 | 1.55e-2 | 2019 Nov 23 | Sy2b
J0407.8$-$6116 | 2MASX J04075215$-$6116126∗ | 04:07:52.1 |  $-$61:16:12.8 | 0.0214 | 10.4 | 1.58e-2 | 2018 May 05 | Ga
J0844.8$+$3055 | 2MASX J08445829$+$3056386∗ | 08:44:58.3 | +30:56:38.3 | 0.0643 | 9.9 | 1.15e-1 | 2018 Jan 03 | AGNb
J0901.8$-$6418 | ESO 090$-$IG 014∗ | 09:01:37.2 |  $-$64:16:28.1 | 0.0220 | 9.9 | 8.29e-3 | 2018 June 01 | IGc
J1108.4$-$1148 | IRAS 11058$-$1131† | 11:08:20.3 |  $-$11:48:12.1 | 0.0548 | 9.7 | 3.83e-3 | 2020 Mar 2 | Sy2b
J1111.0$+$0054 | 2MASX J11110059$-$0053347† | 11:11:00.6 |  $-$00:53:34.9 | 0.0908 | 9.9 | 4.61e-2 | 2020 May 12 | Sy2b
J1258.4$+$7624 | IRAS 12571$+$7643† | 12:58:36.0 | +76:26:41.3 | 0.0634 | 9.9 | 1.95e-2 | 2020 Jan 22 | Ga
J1828.8$+$5021 | MCG $+$08-33-046† | 18:28:48.1 | +50:22:20.9 | 0.0169 | 9.9 | 1.90e-1 | 2020 Jan 24 | Sy2b

Notes:
$*$: From the 100-month BAT Catalog.
$\dagger$: From the 150-month BAT Catalog.
a: Galaxy. Paturel et al. (2003)
b: Seyfert 2 Galaxy. Véron-Cetty & Véron (2006)
c: Interacting Galaxy. Arp & Madore (1987)

##  3 Spectral Analysis Results

Spectral fitting was conducted with XSPEC v. 12.10.1f (Arnaud, 1996). The
Heasoft tool nh (Kalberla et al., 2005) was used to calculate Galactic
absorption in the direction of each source. The flux and intrinsic luminosity
for each source were calculated using
clumin999https://heasarc.gsfc.nasa.gov/xanadu/xspec/manual/node281.html in
xspec. The tables listing the results of the 1$-$7 keV spectral fitting of the
nine Swift-BAT galaxies are reported in the Appendix. In this section, we
introduce the models that are used to analyze the source spectra in $\S$3.1
and the fitting results in $\S$4.

###  3.1 Models Implemented

####  3.1.1 MYTorus

The MYTorus (Murphy & Yaqoob, 2009) model assumes a uniform torus of absorbing
material with circular cross section and a fixed opening angle of 60$\arcdeg$.
The model is composed of three components: the line-of-sight continuum, the
Compton-scattered component (i.e. reflection), and the fluorescent lines. The
line-of-sight continuum, also described as the zeroth-order continuum, is the
intrinsic X-ray emission from the AGN as observed after absorption from the
surrounding torus. Next, the Compton-scattered component models the photons
that scatter into the observer line of sight after interacting with the dust
and gas surrounding the SMBH. In the case the true covering factor of the
source differs from the default MYTorus value, $f_{c}=cos(\theta)=$ 0.5, or a
not negligible time delay exists between the intrinsic emission and the
scattered component, the two components require different normalizations. The
normalization for the scattered component is denoted as $A_{S}$ (Yaqoob,
2012). The final component models the most significant fluorescent lines,
i.e., the Fe K$\alpha$ and Fe K$\beta$ lines, at 6.4 and 7.06 keV,
respectively. This component also has its own normalization, $A_{L}$. $A_{S}$
and $A_{L}$ were fixed to 1 due to the low quality of our spectra. In our
analysis, we also searched for the presence of a thermal component below 1
keV, which is observed in the X-ray spectra of AGN. However, due to the low
count statistic of our spectra at soft X-ray energies, none of our fits was
significantly improved when adding a thermal component (mekal).
In XSPEC notation, our model is defined as:

$\displaystyle ModelA=constant_{1}*phabs*(MYTZ*$ $\displaystyle
zpowerlw+A_{S}*MYTS+A_{L}*MYTL$ $\displaystyle+f_{s}*zpowerlw),$ (1)

where $MYTZ*zpowerlw$ represents the line-of-sight continuum (or the zeroth-
order continuum), $MYTS$ the scattered component, and $MYTL$ the fluorescent
lines. Lastly, $f_{s}$ is the fraction of intrinsic emission that leaks
through the torus rather than being absorbed by the obscuring material. The
MYTorus model can be utilized in two different configurations, designated
‘coupled’ and ‘decoupled’ (Yaqoob, 2012).

####  3.1.2 MYTorus in Coupled Configuration

MYTorus measures the angle between the axis of the torus and the observer line
of sight, known as the torus inclination angle, which will hereafter be
written as $\theta_{obs}$. This angle ranges from 0$\arcdeg-$90$\arcdeg$,
where $\theta_{obs}$ = 90$\arcdeg$ represents edge-on observing and
$\theta_{obs}$ = 0$\arcdeg$ represents face-on observing. When MYTorus is in
the coupled configuration, all three components of the model are set to have
the same $\theta_{obs}$, which is a free parameter, and the same column
density.

####  3.1.3 MYTorus in Decoupled Configuration

The decoupled configuration of MYTorus was initially introduced in Yaqoob
(2012) and adds the flexibility of allowing different values for the line-of-
sight column density, $N_{H,Z}$, and the average torus column density,
$N_{H,S}$; a first approximation to a clumpy distribution. In this
configuration, the line-of-sight continuum is fixed to an angle of
$\theta_{obs,Z}$ = 90$\arcdeg$. The scattered and fluorescent line components
have an equal $\theta_{obs,S,L}$, which can either be fixed to 90$\arcdeg$ or
0$\arcdeg$ to represent edge-on or face-on reflection, respectively. In the
edge-on reflection scenario, the obscuring material between the AGN and the
observer reprocesses the photons. In the face-on reflection scenario, the
emission reflecting off the far side of the torus passes through and is
observed (which could also be a sign of a patchy distribution of material). In
MYTorus decoupled, the scattered and fluorescent line column densities are
represented by $N_{H,S}$, which can vary greatly from the line-of-sight column
density in an inhomogeneous, patchy torus.

####  3.1.4 BORUS02

The second physically motivated model we used to analyze our data is borus02
(Baloković et al., 2018). This model incorporates an absorbed intrinsic
continuum multiplied by a line-of-sight absorbing component, zphabs $\times$
cabs. Additionally, borus02 models the reprocessed component, including the
Compton-scattered component and fluorescent lines. This model includes the
torus covering factor as a free parameter which varies in the range from
$f_{c}$ = 0.1$-$1, equivalent to a torus opening angle $\theta_{tor}$ =
0$\arcdeg-$84$\arcdeg$. borus02 is implemented in XSPEC in the following way:

$\displaystyle ModelB=constant_{1}*phabs*$ (2)
$\displaystyle(borus02+zphabs*cabs*zpowerlw$ $\displaystyle+f_{s}*zpowerlaw),$

where $borus02$ models the reprocessed components, which includes the
scattered continuum and fluorescent line emission. In addition, borus02
includes the high-energy cutoff and iron abundance as free parameters. We
froze the energy cutoff at 500 keV to remain consistent with the default
setting in MYTorus and fixed the iron abundance to 1 due to low statistics in
our data. The zphabs and cabs components account for the line-of-sight
absorption within the source, including Compton scattering losses out of the
line of sight.

##  4 Results

In Figure 1, we report the borus02 best-fit line-of-sight column density as a
function of redshift for the nine objects presented in this paper, as well as
for those obtained in previous works by our group. The subsequent subsections
describe the fitting results for all nine sources. For every source, we
removed from the BAT spectra those data points with error bars compatible with
a non-detection. We note that in the tables of best-fit parameters for the
final five sources, we only list the Chandra cstat/dof as the BAT data showed
poor fitting statistics, likely due to the large intrinsic dispersion. For
example, the BAT data for 2MASX J11110059$-$0053347 had only 10 points yet was
responsible for $\sim$90% of the reduced statistic.
We note that we compared our errors from the model fits with errors calculated
using a Markov Chain Monte Carlo (MCMC)
algorithm101010https://heasarc.gsfc.nasa.gov/xanadu/xspec/manual/node43.html.
As both methods produced similar results, we are confident the errors derived
from the models are valid.
In the Appendix, we show the analysed Chandra images of each source, along
with the corresponding BAT positional uncertainty region at a 95% confidence
level. In each image, the counterpart listed in Table 1 is marked within the
BAT region. The region size is calculated by

$R_{95}(\arcmin)=12.5\times[S/N]^{-0.68}+0.54,$ (3)

where S/N is the significance of the detection (see Cusumano et al., 2010;
Segreto et al., 2010, for details). The size of this region for each source
can be found in Table 12. For the majority of our sources, there is only one
object within the BAT region, making it the clear counterpart. In cases where
it is not as clear, further discussion can be found below, in the respective
subsection detailing the analysis of each object.
We note that the Chandra and BAT data are not taken simultaneously, as BAT
gives an average of the spectrum over 150 months of observation. This implies
our observations are susceptible to being affected by variability. Any non-CT
variability in the line-of-sight column density does not have an impact in our
analysis, given how BAT is sensitive to emission $>15$ keV, an energy range
unaffected by line-of-sight obscuration. However, flux variability between the
two observations can occur, and therefore we have included a Chandra cross-
normalization constant, Ccha, to account for this. It is possible that extreme
flux variability can occur, causing our models to mistakenly classify a source
as highly obscured when it is only in a low-flux state. We note that this has
not happened before and our previous works show that the Chandra$-$BAT
analysis produces reasonably accurate column density measurements (however
with large uncertainties) when compared with the XMM-Newton$-$NuSTAR results
(Marchesi et al., 2017a; Zhao et al., 2019a, b). This is why any of our
sources that are compatible with $N_{H}>10^{24}$ cm-2 must be considered only
a candidate CT-AGN until simultaneous XMM-Newton and NuSTAR observations can
verify the classification.

Figure 1: The line-of-sight column density as a function of redshift. The blue
circles represent the borus02 best fit line-of-sight column densities from the
nine sources in the work, the red diamonds represent the seven sources
analyzed in Marchesi et al. (2017a) with a fixed inclination angle of
90$\arcdeg$, and the green squares represent the results from Marchesi et al.
(2017b). Unfilled shapes are reported as galaxies in SIMBAD (see Table 1). The
four X symbols are Seyfert 1 galaxies. Sources above the dashed line are
candidate Compton-thick AGNs (i.e., having line-of-sight column density NH,Z
$\geq$ 1024 cm-2). The arrow pointed upwards represents a source with only a
lower limit on the line-of-sight NH,Z.

###  4.1 X-ray Spectral Fitting Results

####  4.1.1 ESO 090$-$IG 014

As is visible in Figure 2, there are 2 other X-ray sources in the Chandra
field, 2MASS J09015969$-$6416408 (red) and WISEA J090129.46$-$641551.1
(magenta) that are within or near ($<1\arcmin$) the BAT 95% confidence region
(R $\approx$ 3$\arcmin$). Neither source has any X-ray emission above 3 keV.
Furthermore, ESO 090$-$IG 014 (green) is $\sim$3 magnitudes brighter in the
WISE W3 band, the band most commonly associated with AGN emission (Asmus et
al., 2015). For these reasons, it is highly unlikely that either of the other
two sources would contribute to the Swift-BAT data.
The best fit results are displayed in Table 2. All four models show good
agreement with a soft photon index $\Gamma\approx$ 2.20. ESO 090$-$IG 014 is
one of the sources for which the best fit required a cross-normalization not
equal to 1, C${}_{cha}\approx 0.3$, suggesting that the Chandra observation
was taken in a low-flux epoch. Except MYTorus coupled, all models suggest an
obscured AGN with $N_{H,Z}\approx 4\times 10^{23}$ cm-2. The average torus
column density is lower, on the order of 1022 cm-2, suggesting a clumpy torus.
In the borus02 model, the covering factor and $\theta_{obs}$ were fixed to 0.5
and 87$\arcdeg$ (the upper limit in borus02), respectively, since the data
quality was not high enough to properly constrain them (as suggested by Zhao
et al., 2020). We note these values are consistent with the poorly-constrained
best-fit values. Also, $f_{s}$ is frozen to zero in borus02, given how the
best-fit results yields $f_{s}$ $<$ 10-5, compatible with zero.

Figure 2: The Chandra CCD for the 10 ks of ESO 090$-$IG 014 (marked with the
smaller of the two green circles) in the 1$-$7 keV range. Two other nearby
sources, 2MASS J09015969$-$6416408 (red) and WISEA J090129.46$-$641551.1
(magenta), were studied and are believed to have not contributed to the BAT
emission (see the text for further details). The large green circle
(2.87$\arcmin$ in radius, see Table 12) represents the 95% Swift-BAT
confidence region. Table 2: ESO 090$-$IG 014

Model | MYTorus | MYTorus | MYTorus | borus02
---|---|---|---|---
| (Coupled) | (Decoupled Face-on) | (Decoupled Edge-on) |
cstat/dof | 43/27 | 42/27 | 42/27 | 40/27
$\Gamma$ | 2.19${}^{+0.17}_{-0.18}$ | 2.17${}^{+0.17}_{-0.17}$ | 2.21${}^{+0.16}_{-0.17}$ | 2.12${}^{+0.16}_{-0.18}$
$N_{H,eq}$ | 1.35${}^{+1.90}_{-1.03}$ | … | … | …
norm $10^{-2}$ | 0.42${}^{+0.09}_{-0.07}$ | 0.50${}^{+0.14}_{-0.09}$ | 0.60${}^{+0.08}_{-0.06}$ | 0.44${}^{+0.02}_{-0.02}$
cf,Tor | … | … | … | 0.5*
cos($\theta_{obs}$) | 0.49${}^{+}_{-0.01}$ | … | … | 0.05*
$N_{H,Z}$ | … | 0.37${}^{+0.12}_{-0.10}$ | 0.42${}^{+0.16}_{-0.08}$ | 0.40${}^{+0.10}_{-0.09}$
$N_{H,S}$ | … | 0.01${}^{+0.25}_{-}$ | 0.03${}^{-}_{-}$ | 0.01${}^{+0.23}_{-}$
$f_{s}$ 10-2 | 0.20${}^{+0.23}_{-0.17}$ | 0.24${}^{+0.33}_{-}$ | 0.07${}^{+0.26}_{-}$ | 0*
Ccha | 0.34${}^{+0.21}_{-0.14}$ | 0.30${}^{+0.17}_{-0.11}$ | 0.32${}^{+0.20}_{-0.17}$ | 0.34${}^{+0.20}_{-0.06}$
L$\rm{}_{2-10\,keV}$ |  |  |  | 1.02${}^{+0.24}_{-0.19}$ $\times$ 1043
L$\rm{}_{15-55\,keV}$ |  |  |  | 6.46${}^{+0.62}_{-0.57}$ $\times$ 1042

Notes:
*: Parameter was frozen to this value during fitting.
${}^{-}_{-}$: Parameter is unconstrained.
$\Gamma$: Power law photon index.
NH,eq: Hydrogen column density along the equator of the torus in units of 1024
cm-2.
norm: the main power-law normalization (in units of photons cm2 s-1 keV-1
$\times$ 10-4), measured at 1 keV.
cf,Tor: Covering factor of the torus.
cos($\theta_{obs}$): Cosine of the inclination angle.
$N_{H,Z}$: Line-of-sight torus hydrogen column density, in units of 1024 cm-2.
$N_{H,S}$: Average torus hydrogen column density, in units of 1024 cm-2.
$f_{s}$: Fraction of scattered continuum.
Ccha: The cross-normalization constant between the Chandra and Swift-BAT data.
L$\rm{}_{2-10\,keV}$: Intrinsic luminosity in the 2$-$10 keV band with units
of erg s-1.
L$\rm{}_{15-55\,keV}$: Intrinsic luminosity in the 15$-$55 keV band with units
of erg s-1.

####  4.1.2 2MASX J02051994$-$0233055

The 150-month catalog lists 2MASX J02051994$-$0233055 (green in Figure 8) as
the counterpart of the BAT emission. The 105-Month Swift-BAT catalog (Oh et
al., 2018), however, includes a BAT source that overlaps with the one studied
here, with WISEA J020527.94$-$023321.8 (red) listed as its counterpart. We
mark the position of both possible counterparts in the Chandra field image in
Appendix B, showing that there is no Chandra emission coming from WISEA
J020527.94$-$023321.8. Moreover, WISEA J020527.94$-$023321.8 is $\sim$4
magnitudes dimmer in the W3 band. The counterpart of the BAT emission is thus
2MASX J02051994$-$0233055.

While the majority of the models for 2MASX J02051994$-$0233055 are in
agreement, the MYTorus decoupled edge-on configuration yielded significantly
different results in the line-of-sight column density (8.6${}^{+4.0}_{-2.5}$
$\times$ 1023 cm-2). The other three models suggest a heavily CT-AGN with
line-of-sight column density N${}_{H,Z}>>$ 1024 cm-2. According to the borus02
model results, displayed in Figure 5, the spectrum is reflection dominated.
We tested the reliability of the reflection-dominated scenario using the
pexmon model as follows:

$\displaystyle ModelC=constant*phabs*(zphabs*zpowerlw+$ (4) $\displaystyle
pexmon+f_{s}*zpowerlw).$

pexmon is a neutral Compton reflection model with self-consistent Fe and Ni
lines (George & Fabian, 1991; Nandra et al., 2007). It includes a scaling
factor, R, which allows to consider (R = 1) or exclude (R $<$ 0) the intrinsic
emission component. We opt for the latter, as the inclusion of
zphabs*zpowerlaw allows to estimate the line of sight column density. The best
fit line-of-sight column density for the pexmon model is NH,Z =
5.54${}^{+5.76}_{-3.44}$ $\times$ 1024 cm-2.
Finally, we also attempt to model the source using the MYTorus decoupled model
in a combination of both face-on and edge-on configurations. This model is
consistent with the MYTorus coupled, MYTorus decoupled face-on, and borus02
results, with best-fit estimations all suggesting line-of-sight and average
column densities on the order of 1025 cm-2. Based on the results derived from
all models, we believe 2MASX J02051994$-$0233055 to be a reliable CT-AGN
candidate.

####  4.1.3 2MASX J04075215$-$6116126

ESO 118$-$IG 004 (red in Figure 8) was originally listed as the most reliable
counterpart for 4PBC J0407.8$-$6116 as it is bright in the W3 band
($\sim$7.5). However, the analysis of the Chandra data allowed us to challenge
this claim, and determine that 2MASX J04075215$-$6116126 (green) is the true
source of the BAT emission. As seen in Appendix B, 2MASX J04075215$-$6116126
is at the center of the BAT 95% confidence region, while ESO 118$-$IG 004 is
located just outside of it. Also, 2MASX J04075215$-$6116126 has a count rate
(in the 2$-$10 keV band) more than 15 times greater than that of ESO 118$-$IG
004. Furthermore, ESO 118$-$IG 004 shows a flux decay toward higher energies,
while 2MASX J04075215$-$6116126 shows an increase consistent with a Compton-
thin source. However, it is not impossible that ESO 118$-$IG 004 is a highly
CT source that contributes in a non-negligible way to the BAT flux. For this
reason, we have been awarded NuSTAR + XMM simultaneous observations to study
these sources and verify their column densities.
We note that the source WISEA J040732.53$-$611918.3 (magenta) is also present
in the Chandra image, located just outside of the BAT confidence region.
However, it is $\sim$5 times dimmer in X-rays and $\sim$3 magnitudes dimmer in
the W3 band. Therefore, we do not believe it contributes to the BAT flux.
The four models used agree on most parameters. All estimate a photon index
$\Gamma\approx$ 1.60 with only 7% errors and a line-of-sight column density
around 2.0$\times$1023 cm-2. The reflection component parameters are less
tightly constrained due the fact that, in this particular source, reflection
is subdominant. The average torus column density is similar to the line-of-
sight value, $\approx$ 2.0$\times$1023 cm-2, however with uncertainties
greater than half an order of magnitude. The borus02 model yields a value of
0.90 for both the covering factor and the cosine of the inclination angle
although largely unconstrained.

####  4.1.4 2MASX J08445829$+$3056386

2MASX J08445829$+$3056386 was also detected in the 105-Month BAT catalog under
the counterpart name FBQS J084458.3+305638.
In this work, all four models are in good agreement with most parameters,
including an average AGN photon index of $\Gamma\approx$ 1.75. The two MYTorus
decoupled models and borus02 suggest this is a Compton-thin AGN with an NH,Z
of the order of 1022 cm-2. This result is consistent with the fact that the
source has a high count rate, 0.115 ct s-1, which would be unusual for a
Swift-BAT-detected CT-AGN at $z\sim 0.07$. The borus02 model cannot constrain
$\theta_{obs}$, so it was fixed to cos($\theta_{obs}$) = 0.05. In addition,
the scattering constant $f_{s}$ is also fixed to zero due to its best-fit
result being compatible with zero, i.e., $f_{s}<$ 10-5.

####  4.1.5 2MASX J11110059$-$0053347

All four models displayed in Table 7 show consistent NH,Z values $\sim$
7$\times$1022 cm-2, signaling a Compton-thin AGN. The photon index was well
constrained around $\Gamma$=1.65 with $\sim$5% errors. As evidenced by the low
obscuration measured for this source, we conclude the intrinsic emission
dominates over the reflection component. Therefore, we were unable to provide
any constraint on the torus parameters derived from the reflection component
such as the average torus column density, the inclination angle, and the
covering factor.

####  4.1.6 ESO 549$-$50

All models yielded a well-constrained average photon index of $\Gamma\approx$
1.85 with only 10% uncertainties. Moreover, the four best-fit results are in
agreement with an NH,Z $\approx$ 3$\times$1023 cm-2, indicating this source is
significantly obscured. While the covering factor appears to be well
constrained around 0.35, neither the inclination angle nor the average torus
column density are. The average torus column density is only loosely
constrained (N${}_{H,tor}>$ 1023).

####  4.1.7 IRAS 11058$-$1131

The Chandra image in Appendix B shows IRAS 11058$-$1131 surrounded by several
hot pixels, as well as the source 2MASS J11083339$-$1151500 (red in Figure 9)
near the bottom of the BAT region. Upon further inspection, it was revealed
the latter does not have emission above 3 keV and is $\sim$ 4 magnitudes
fainter in the WISE W3 band. Thus, is unlikely to be the true BAT counterpart.
As can be seen in Figure 7, this source has a significant drop-off in flux in
the Chandra data compared to the BAT data. For this reason, we let the Chandra
cross-normalization constant, $C_{cha}$, free to vary and fixed the BAT
constant to 1. Most of the models have a $C_{cha}$ value $<1$, although with
large uncertainties. IRAS 11058$-$1131 is best-fit with a high NH,Z value as
exemplified by the large decrease in the soft-energy band. These values range
from Compton-thin, 8$\times$1023 cm-2, to CT, 2.6$\times$1024 cm-2. Since both
of these results are statistically equivalent, we list IRAS 11058$-$1131 as a
CT-AGN candidate. The average torus column density shows better agreement
among the three applicable models with values in the CT regime. The photon
index is rather hard, averaging $\Gamma\sim$1.43.

####  4.1.8 MCG $+$08-33-046

The Chandra observation of MCG $+$08-33-046 is significantly affected by pile-
up (over 20% according to the Chandra pileup tool, Davis, 2001). Considering
this tool is only applicable to a power law, we were unable to utilize the
models discussed in Section 3.1. With the pileup tool implemented, the best-
fit has a photon index $\Gamma\sim$2 and an NH,Z $\approx$ 2$\times$1022 cm-2.
This low line-of-sight column density agrees well with the high flux levels of
this source in the soft X-rays.

####  4.1.9 IRAS 12571$+$7643

We originally assumed PGC 044558 (red Figure 10) as the most likely
counterpart of the BAT source, due to its Sy2 nature. However, there is no
emission from this source in the Chandra exposure. As there is significant
emission from IRAS 12571+7643 (green), which is also within the BAT 95%
confidence region, we believe this is the true source of the BAT emission.
This is another Compton-thin candidate, with NH,Z $\approx$ 1.7$\times$1023
cm-2. Most fits yielded an average column density on the order of 1022 cm-2,
significantly less than the line-of-sight NH. This is only the third source in
this sample to have NH,Z $>$ NH,S. The photon index was consistently around
$\Gamma\sim$1.7 with $<$ 8% uncertainties.

###  4.2 Mid-IR Comparison

The Mid-infrared (MIR) is another useful waveband to select CT-AGN candidates.
As the ultraviolet (UV) emission from the accretion disk gets absorbed by the
dusty torus, it becomes heated to temperatures of several hundred Kelvins. As
a result, the dust radiates thermally, with its emission peaking in the MIR
($\sim$3 - 30 $\mu$m, Asmus et al., 2020). As this emission is much less
susceptible to absorption, many works have used the MIR to identify heavily
obscured AGN (Yan et al., 2019; Asmus et al., 2020; Kilerci Eser et al., 2020;
Guo et al., 2021). Moreover, Asmus et al. (2015) used a sample of 152 AGN with
reliable soft X-ray data to model a trend between the intrinsic 2$-$10 keV
luminosity and the 12$\mu$m luminosity (see Figure 3). In addition, we have
plotted the intrinsic (closed circles) and observed (open circles) X-ray
luminosities of the sources in this work, and those of recently confirmed CT-
AGN (Marchesi et al., 2019; Zhao et al., 2019a, b; Torres-Albà et al., 2021;
Traina et al., 2021). The two green stars represent the candidate CT-AGN
presented in this work, 2MASX J02051994$-$0233055 and IRAS 11058$-$1131\. It
can be seen, 2MASX J02051994$-$0233055 shows a significant decrease from
intrinsic to observed luminosity and IRAS 11058$-$1131 has an observed
luminosity near the CT region. Both are strong indicators of a CT-AGN.

Figure 3: The 2$-$10 keV vs 12$\mu$m luminosities of the nine sources in this
work. The filled circles represent the intrinsic 2$-$10 keV luminosities,
while the open circles represent the observed luminosities. The green stars
are the two candidate CT-AGN presented in this work, 2MASX J02051994$-$0233055
and IRAS 11058$-$1131\. The black line is the relation derived from the X-ray
observations of a reliable sample of 152 AGN presented in Asmus et al. (2015).
The blue circles are recently confirmed CT-AGN (Marchesi et al., 2019; Zhao et
al., 2019a, b; Torres-Albà et al., 2021; Traina et al., 2021). The grey area
represents a 25$\times$ (or more) decrease in X-ray flux, a diagnostic used to
identify CT-AGN (Annuar et al., 2020). The 12$\mu$m data were obtained by
WISE.

##  5 Study of Extended Emission

The radiation from the accretion disk of an AGN is collimated by the torus,
given how it is symmetric around the accretion flow axis. The radiation
escaping from the AGN excites the gas of the interstellar medium (ISM) by
photoionization, which appears in the form of cones extending from the
nucleus. These cones have been observed in local Seyfert galaxies in NIR and
optical (e.g. Durré & Mould, 2018), as well as X-rays (Fabbiano et al., 2017,
2018; Jones et al., 2020; Ma et al., 2020). In X-rays, the mentioned works
have used Chandra’s unmatched resolution to observe kiloparsec-scale diffuse
emission in both the hard continuum (3$-$7 keV) and in the Fe-K$\alpha$ line.
Obscured, and particularly CT-AGN, are ideal to observe this extended X-ray
emission given how the torus dims the much brighter nuclear emission.
We take advantage of our high-resolution Chandra images and attempt to detect
the cone emission in the highly obscured sources presented in this work. In
order to do so, we extract radial profiles from all of our sources and compare
them to the expected radial profile of a point source of the same flux and in
the same position. We follow the CIAO Point-Source Functions (PSF) simulation
thread111111https://cxc.harvard.edu/ciao/threads/psf.html
121212https://cxc.harvard.edu/ciao/threads/marx_sim/ and generate the Chandra
PSFs using ChaRT 131313https://cxc.harvard.edu/ciao/PSFs/chart2/ and MARX
5.5.1141414https://cxc.harvard.edu/ciao/threads/marx/. Figure 4 shows a
comparison between a simulated PSF and the observed emission, for the case of
2MASX J11110059$-$0053347\. The two curves are compatible with each other, and
there is no significant excess over the the simulated data counts. All sources
in our sample show similar curves, and thus no sign of extended X-ray
emission. 2MASX J11110059$-$0053347 has a count rate twice as high as the 10
ks exposure of MKN 573, a CT-AGN source analyzed in (Jones et al., 2021),
which presents significant extended emission. Therefore, the ionization cone
in the sources of our sample is either much fainter, or not present.

Figure 4: The 3$-7$ keV radial profile of 2MASX J11110059$-$0053347 compared
to that of a simulated point source. The two curves are compatible, and
therefore there is no significant evidence of extended emission. A similar
trend exists for the other eight sources in this paper.

##  6 Discussion and Conclusions

In this paper, we presented the joint Chandra–Swift-BAT spectral fitting
analysis in the 1$-$150 keV energy range for nine nearby ($z<$ 0.1) AGN
selected from the 150-month Swift-BAT all-sky survey catalog. This represents
the second step of our three step plan to discover new Compton-thick AGN in
the local Universe. Our first step was selecting these sources following
previous successful selection criteria (Marchesi et al., 2017a, and see Sect.
2) and acquiring Chandra snapshot observations for each of them. The third and
final step will involve obtaining and analyzing XMM-Newton and NuSTAR
observations of the best CT-AGN candidates found in this work. We identified
these candidates by fitting the Swift-BAT and Chandra spectra with several
models in order to constrain spectral parameters such as the intrinsic
absorption, NH,Z, and photon index, $\Gamma$, to uncover highly obscured AGN.
The borus02 best-fit parameters for each source are listed in Table 3.

Table 3: Results for the Entire Sample

Source | ESO 090 | 2MASX J0205 | 2MASX J0407 | 2MASX J0844 | 2MASX J1111 | ESO 549 | IRAS 110 | MCG $+$08 | IRAS 125
---|---|---|---|---|---|---|---|---|---
cstat/dof | 40/27 | 57/72 | 57/31 | 201/170 | 98/74 | 21/23 | 11/6 | 86/77 | 41/30
$\Gamma$ | 2.12${}^{+0.16}_{-0.18}$ | 1.65${}^{+0.09}_{-0.22}$ | 1.56${}^{+0.09}_{-0.14}$ | 1.74${}^{+0.07}_{-0.06}$ | 1.77${}^{+0.02}_{-0.19}$ | 1.91${}^{+0.02}_{-0.02}$ | 1.45${}^{+0.35}_{-}$ | 2.05 | 1.61${}^{+0.18}_{-0.07}$
$N_{H,eq}$ | … | … | … | … | … | … | .. | 0.02 | …
norm $10^{-2}$ | 0.44${}^{+0.02}_{-0.02}$ | 0.27${}^{+1.23}_{-0.16}$ | 0.04${}^{+0.02}_{-0.01}$ | 0.09${}^{+0.01}_{-0.01}$ | 0.06${}^{+0.02}_{-0.01}$ | 0.10${}^{+0.10}_{-0.02}$ | 0.04${}^{+0.16}_{-0.02}$ | 0.32 | 0.05${}^{+0.02}_{-0.01}$
cf,Tor | 0.5* | 0.87${}^{+0.11}_{-0.46}$ | 0.90${}^{-}_{-0.85}$ | 1.00${}^{-0.65}_{-}$ | 0.89${}^{-}_{-}$ | 0.35${}^{+0.05}_{-0.05}$ | 0.60${}^{-}_{-}$ | … | 0.15${}^{-}_{-}$
cos($\theta_{obs}$) | 0.05* | 0.78${}^{+0.21}_{-0.51}$ | 0.90${}^{-}_{-}$ | 0.05* | 0.89${}^{-}_{-}$ | 0.95${}^{-}_{-0.77}$ | 0.05* | … | 0.90${}^{-}_{-}$
$N_{H,Z}$ | 0.40${}^{+0.10}_{-0.09}$$\dagger$ | 10.00*$\dagger$ | 0.21${}^{+0.04}_{-0.08}$ | 0.030 ${}^{+0.003}_{-0.003}$$\dagger$ | 0.07${}^{+0.02}_{-0.02}$ | 0.26${}^{+0.08}_{-0.06}$ | 0.81${}^{+0.84}_{-0.74}$ | … | 0.16${}^{+0.05}_{-0.03}$
$N_{H,S}$ | 0.01${}^{+0.23}_{-}$ | 10.00${}^{-}_{-6.45}$ | 0.19${}^{+2.32}_{-0.15}$ | 0.24${}^{+0.22}_{-0.15}$ | 31.62${}^{-}_{-}$ | 14.13${}^{-}_{-}$ | 7.41${}^{-}_{-}$ | … | 0.01${}^{-}_{-}$
$f_{s}$ 10-2 | 0* | 4.08${}^{+11.90}_{-2.63}$ | 2.03* | 0* | 0.03${}^{+0.04}_{-0.03}$ | 0* | 0.03${}^{-}_{-}$ | … | 0.01${}^{+0.01}_{-}$
Ccha | 0.34${}^{+0.20}_{-0.06}$ | 1* | 1* | 1* | 1* | 1* | 0.70${}^{+5.30}_{-0.69}$ | 1* | 1*
L$\rm{}_{2-10\,keV}$ | 1.02 $\times$ 1043 | 1.10 $\times$ 1042 | 1.51 $\times$ 1042 | 3.31 $\times$ 1043 | 3.98 $\times$ 1043 | 3.98 $\times$ 1042 | 1.55 $\times$ 1043 | 4.90 $\times$ 1042 | 2.09 $\times$ 1043
L$\rm{}_{15-55\,keV}$ | 6.46 $\times$ 1042 | 3.98 $\times$ 1042 | 3.16 $\times$ 1042 | 3.89 $\times$ 1043 | 5.01 $\times$ 1043 | 3.72 $\times$ 1042 | 3.16 $\times$ 1043 | 3.55 $\times$ 1042 | 3.63 $\times$ 1043

Notes: Same as Table 2.
$\dagger$: At least one of the models has a significantly different best-fit
$N_{H,Z}$ value.

###  6.1 Model Comparison

The two configurations of MYTorus decoupled, face-on and edge-on, and borus02
were capable of satisfactorily fitting all sources, while MYTorus coupled
yielded agreeing values in most cases. As previously discussed, the poor data
quality in this sample required us to freeze multiple parameters (typically
covering factor and/or inclination angle) in borus02, and to use a simplified
version of MYTorus decoupled (adopting either an edge-on or face-on scenario,
instead of a combination of both). While these simplifications, and the low
count statistics, do not allow us to use the model complexity to estimate
average torus properties, they accomplish the main goal of this paper:
providing an estimate of the line-of-sight column density. This allows us to
classify them as either candidate CT-AGN, or as likely C-thin sources. Here we
discovered two new CT-AGN candidates, 2MASX J02051994$-$0233055 and IRAS
11058$-$1131.

For two sources we implemented additional models, to ascertain their nature.
For 2MASX J02051994$-$0233055 we used a phenomenological model (pexmon) to
confirm the dominance of the reflection component. For MCG $+$08$-$33$-$046 we
used only a simple absorbed power law, given how XSPEC provides a tool to
treat pile-up that is applicable only to a power law (pileup_map Davis, 2001).
Given all the mentioned limitations, and the need to freeze the parameters
that constrain the main torus properties, we have opted not to implement more
complex models (i.e. UXClumpy, which models a clumpy torus scenario, Buchner
et al., 2019). We leave this interesting possibility for a follow-up project,
using joint XMM-Newton and NuSTAR observations, on the two newly discovered
CT-AGN candidates (Silver et al. in prep.).

###  6.2 Efficiency of Selection Criteria

We selected nine high-latitude ($|b|>$ 10$\arcdeg$) sources from the BAT 150
month catalog that lacked a ROSAT counterpart (0.1 $-$ 2.4 keV) and are
classified as galaxies or Seyfert 2 galaxies. As discussed in Section 4, all
nine sources exhibit some level of obscuration, with a line-of-sight Hydrogen
column density $\geq$ 1022 cm-2. However, three of the sources analysed in
this work have logNH,Z $<$ 23, while those analysed by Marchesi et al. (2017a)
were all above this threshold. According to the selection criteria used, the
lack of a ROSAT counterpart should imply an obscuration of at least logNH,Z
$\geq$ 23 (Koss et al., 2016). We believe this increase in sources with lower
levels of obscuration could be caused by our sampling of fluxes fainter than
before. In particular, the sources selected in this work are selected from the
150-month BAT catalogue (Segreto et al. in prep.), and were not detected in
the previous 100-month version (Cusumano et al., 2014). This makes them
intrinsically fainter than those selected in Marchesi et al. (2017a).
Furthermore, we performed simulations in
WebSpec151515https://heasarc.gsfc.nasa.gov/webspec/webspec.html testing at
which column densities our high $z$ ($z>$ 0.05) sources no longer became
detectable by ROSAT. This occurred at column densities as low as 5 $\times$
1022 cm-2, well below the 1 $\times$ 1023 cm-2 predicted by Ajello et al.
(2008) and Koss et al. (2016). Therefore, the lack of ROSAT counterpart is not
as predictive of heavily obscured AGN as initially assumed.

In any case, our results, together with those presented in Marchesi et al.
(2017a) and Marchesi et al. (2017b), show that within uncertainties, 29/30
sources are obscured AGN and 5 (i.e., 17 $\pm$ 7%) of the sources selected
through our previously mentioned criteria are classified as CT-AGN candidates
based on the Chandra-BAT analysis. However, the necessity of targeting local
sources (with these criteria) becomes clear when comparing the best-fit
results of sources with $z<$ 0.04 and $z\geq$ 0.04. At $z<$ 0.04, we see a
success rate to discover CT-AGN of 4/20 (20 $\pm$ 10%) and an average
$N_{H,Z}$ = 8.95$\times$1023 cm-2. In contrast, at $z\geq$ 0.04 we have a
success rate of 1/10 (10 $\pm$10%) and an average $N_{H,Z}$ = 2.24$\times$1023
cm-2, approximately a quarter of that of the $z<$ 0.04 sources. Moreover, only
4 out of the 20 sources (20 $\pm$ 10%) at $z<$ 0.04 have a best-fit $N_{H,Z}<$
1023 cm-2, while 4 out of 10 (40 $\pm$ 20%) do for $z\geq$ 0.04. Note that in
a blind survey (see, e.g. Burlon et al., 2011) only about 5% of AGN are found
to be CT, suggesting these criteria remain a powerful tool to find heavily
obscured, and especially CT, AGN.
Besides redshift, an important selection criterion is the source optical
classification. All 5 potential CT-AGN candidates are either Seyfert 2s or are
galaxies without a reliable optical classification (i.e. galaxy, galaxy in
pair, AGN; Segreto et al. in prep.). Sources that cannot be easily classified
based on their optical spectra are more likely to be Type 2 AGN, given how the
obscuration can hinder the detection of features needed for an accurate
classification161616We note that galaxies not optically classified as AGN with
detected BAT emission are likely to be AGN, since their luminosities in the
$>15$ keV band are $>10^{42}$ erg s-1.. Moreover, none of the four Seyfert 1s
in Marchesi et al. (2017b) are Compton thick and two are the least obscured
sources in the full sample of 30.

###  6.3 Future Work

This work is part of an ongoing effort to identify and characterize all CT-
AGNs in the local ($z<0.1$) universe (The Clemson Compton-Thick AGN
project171717https://science.clemson.edu/ctagn/). In order to do so, we plan
on:

  * •

Increasing the count statistics used on the most promising candidates. Two
potential CT-AGN, 2MASX J02051994$-$0233055 and ESO 118$-$IG 004, have been
accepted for joint XMM-Newton and NuSTAR observations for 30 ks and 80 ks,
respectively (Cycle 6, PI: M. Ajello). The increased exposure time and
sensitivity of the instruments will allow us to better characterize these CT-
AGN candidates.

  * •

Implementing patchy torus models like UXClumpy utilizing the improved count
statistics from XMM-Newton and NuSTAR.

  * •

Increasing the sample size of potential CT-AGNs. With the recent release of
the 150-month Swift-BAT all-sky survey catalog, there are additional sources
meeting our criteria that have never been observed by Chandra, XMM-Newton, or
NuSTAR. We plan to target these sources with future observations.

RS, NTA, AP, and MA acknowledge NASA funding under contracts 80NSSC20K0045,
80NSSC19K0531, and 80NSSC21K0016 and SAO funding under contracts GO0-21083X
and G08-19083X. SM acknowledges funding from the the INAF “Progetti di Ricerca
di Rilevante Interesse Nazionale” (PRIN), Bando 2019 (project: “Piercing
through the clouds: a multiwavelength study of obscured accretion in nearby
supermassive black holes”).

##  Appendix A Best Fit Parameters

Figure 5: Unfolded Chandra (black) and BAT (red) spectrum of each source
fitted with the borus02 model. The best-fitting line-of-sight component is
plotted as a solid line, while the reflection component is a dashed line and
the scattered component is a dotted line. The confidence contours at 68%, 90%,
and 99% are displayed for $\Gamma$ and NH,Z (in units of 1022 cm-2). Figure 6:
Unfolded Chandra (black) and BAT (red) spectrum of each source fitted with the
borus02 model. The best-fitting line-of-sight component is plotted as a solid
line, while the reflection component is a dashed line and the scattered
component is a dotted line. The confidence contours at 68%, 90%, and 99% are
displayed for $\Gamma$ and NH,Z (in units of 1022 cm-2). Figure 7: Unfolded
Chandra (black) and BAT (red) spectrum of each source fitted with the borus02
model. The best-fitting line-of-sight component is plotted as a solid line,
while the reflection component is a dashed line and the scattered component is
a dotted line. The confidence contours at 68%, 90%, and 99% are displayed for
$\Gamma$ and NH,Z (in units of 1022 cm-2). Table 4: 2MASX J02051994$-$0233055

Model | MYTorus | MYTorus | MYTorus | MYTorus | borus02 | pexmon
---|---|---|---|---|---|---
| (Coupled) | (Decoupled Face-on) | (Decoupled Edge-on) | Face-on + Edge-on |  |
cstat/dof | 59/73 | 59/73 | 69/73 | 59/74 | 57/72 | 72/74
$\Gamma$ | 1.78${}^{+0.13}_{-0.10}$ | 1.73${}^{+0.03}_{-0.13}$ | 1.76${}^{+0.13}_{-0.14}$ | 1.76${}^{+0.02}_{-0.03}$ | 1.65${}^{+0.09}_{-0.22}$ | 1.83${}^{+0.20}_{-0.19}$
$N_{H,eq}$ | 10.00${}^{-}_{-3.80}$ | … | … | … | … | 5.54${}^{+5.76}_{-3.44}$
norm $10^{-2}$ | 0.64${}^{+0.07}_{-0.06}$ | 0.18${}^{+0.18}_{-0.02}$ | 0.13${}^{+0.13}_{-0.07}$ | 0.18${}^{+0.02}_{-0.01}$ | 0.27${}^{+1.23}_{-0.16}$ | 0.09${}^{+0.10}_{-0.05}$
cf,Tor | … | … | … | … | 0.87${}^{+0.11}_{-0.46}$ | …
cos($\theta_{obs}$) | 0.25${}^{+0.08}_{-0.08}$ | … | … | … | 0.78${}^{+0.21}_{-0.51}$ | 0.5*
$N_{H,Z}$ | … | 10.00${}^{-}_{-7.40}$ | 0.86${}^{+0.40}_{-0.25}$ | 10.00${}^{-}_{-7.30}$ | 10.00* | …
$N_{H,S}$ | … | 10.00${}^{-}_{-5.80}$ | 5.0${}^{-}_{-4.05}$ | 10.00${}^{-}_{-5.80}$ | 10.00${}^{-}_{-6.45}$ | …
$f_{s}$ 10-2 | 1.90${}^{+4.60}_{-1.29}$ | 6.69${}^{+5.31}_{-3.09}$ | 9.29${}^{+8.01}_{-4.04}$ | 6.72${}^{+5.28}_{-3.22}$ | 4.08${}^{+11.90}_{-2.63}$ | 13.19${}^{+16.49}_{-7.71}$
Ccha | 1* | 1* | 1* | 1* | 1* | 1*
L$\rm{}_{2-10\,keV}$ |  |  |  |  | 2.08${}^{+0.08}_{-0.10}$ $\times$ 1043 |
L$\rm{}_{15-55\,keV}$ |  |  |  |  | 3.00${}^{+0.70}_{-0.59}$ $\times$ 1043 |

Notes: Same as Table 2.

Table 5: 2MASX J04075215$-$6116126

Model | MYTorus | MYTorus | MYTorus | borus02
---|---|---|---|---
| (Coupled) | (Decoupled Face-on) | (Decoupled Edge-on) |
cstat/dof | 57/32 | 56/32 | 57/32 | 57/31
$\Gamma$ | 1.61${}^{+0.12}_{-0.12}$ | 1.60${}^{+0.13}_{-0.10}$ | 1.60${}^{+0.13}_{-0.11}$ | 1.56${}^{+0.09}_{-0.14}$
$N_{H,eq}$ | 0.30${}^{+0.59}_{-0.15}$ | … | … | …
norm $10^{-2}$ | 0.04${}^{+0.03}_{-0.02}$ | 0.04${}^{+0.03}_{-0.02}$ | 0.04${}^{+0.03}_{-0.02}$ | 0.04${}^{+0.02}_{-0.01}$
cf,Tor | … | … | … | 0.90${}^{-}_{-0.85}$
cos($\theta_{obs}$) | 0.37${}^{+0.12}_{-}$ | … | … | 0.90${}^{-}_{-}$
$N_{H,Z}$ | … | 0.20${}^{+0.07}_{-0.06}$ | 0.20${}^{+0.08}_{-0.06}$ | 0.21${}^{+0.04}_{-0.08}$
$N_{H,S}$ | … | 0.39${}^{+0.57}_{-}$ | 0.20${}^{+0.64}_{-}$ | 0.19${}^{+2.32}_{-0.15}$
$f_{s}$ 10-2 | 2.37${}^{+3.10}_{-}$ | 2.37${}^{+2.90}_{-2.30}$ | 2.54${}^{+3.10}_{-}$ | 2.03*
Ccha | 1* | 1* | 1* | 1*
L$\rm{}_{2-10\,keV}$ |  |  |  | 2.09${}^{+0.37}_{-0.35}$ $\times$ 1042
L$\rm{}_{15-55\,keV}$ |  |  |  | 3.16${}^{+0.31}_{-0.28}$ $\times$ 1042

Notes: Same as Table 2.

Table 6: 2MASX J08445829$+$3056386

Model | MYTorus | MYTorus | MYTorus | borus02
---|---|---|---|---
| (Coupled) | (Decoupled Face-on) | (Decoupled Edge-on) |
cstat/dof | 204/171 | 203/171 | 205/171 | 201/170
$\Gamma$ | 1.77${}^{+0.05}_{-0.04}$ | 1.77${}^{+0.07}_{-0.05}$ | 1.75${}^{+0.06}_{-0.05}$ | 1.74${}^{+0.07}_{-0.06}$
$N_{H,eq}$ | 0.43${}^{+0.44}_{-0.30}$ | … | … | …
norm $10^{-2}$ | 0.10${}^{+0.01}_{-0.01}$ | 0.10${}^{+0.01}_{-0.01}$ | 0.10${}^{+0.01}_{-0.01}$ | 0.09${}^{+0.01}_{-0.01}$
cf,Tor | … | … | … | 1.00${}^{-}_{-0.65}$
cos($\theta_{obs}$) | 0.50${}^{-}_{-0.02}$ | … | … | 0.05∗
$N_{H,Z}$ | … | 0.031${}^{+0.003}_{-0.003}$ | 0.031${}^{+0.003}_{-0.003}$ | 0.030 ${}^{+0.003}_{-0.003}$
$N_{H,S}$ | … | 0.50${}^{+0.62}_{-0.35}$ | 0.30${}^{+0.42}_{-0.23}$ | 0.24${}^{+0.22}_{-0.15}$
$f_{s}$ 10-2 | 0.02${}^{+2.18}_{-}$ | 0.01${}^{+2.29}_{-}$ | 0.01${}^{+2.34}_{-}$ | 0*
Ccha | 1* | 1* | 1* | 1*
L$\rm{}_{2-10\,keV}$ |  |  |  | 3.31${}^{+0.16}_{-0.15}$ $\times$ 1043
L$\rm{}_{15-55\,keV}$ |  |  |  | 3.89${}^{+0.38}_{-0.34}$ $\times$ 1043

Notes: Same as Table 2.

Table 7: 2MASX J11110059$-$0053347

Model | MYTorus | MYTorus | MYTorus | borus02
---|---|---|---|---
| (Coupled) | (Decoupled Face-on) | (Decoupled Edge-on) |
cstat/dof | 98/74 | 99/74 | 97/74 | 98/74
$\Gamma$ | 1.63${}^{+0.07}_{-0.06}$ | 1.64${}^{+0.07}_{-0.08}$ | 1.69${}^{+0.09}_{-0.08}$ | 1.77${}^{+0.02}_{-0.19}$
$N_{H,eq}$ | 0.07${}^{+0.25}_{-0.01}$ | … | … | …
norm $10^{-2}$ | 0.05${}^{+0.01}_{-0.01}$ | 0.06${}^{+0.01}_{-0.02}$ | 0.06${}^{+0.02}_{-0.01}$ | 0.06${}^{+0.02}_{-0.01}$
cf,Tor | … | … | … | 0.89${}^{-}_{-}$
cos($\theta_{obs}$) | 0.0${}^{+0.5}_{-}$ | … | … | 0.89${}^{-}_{-}$
$N_{H,Z}$ | … | 0.07${}^{+0.02}_{-0.02}$ | 0.06${}^{+0.02}_{-0.02}$ | 0.07${}^{+0.02}_{-0.02}$
$N_{H,S}$ | … | 0.01${}^{-}_{-}$ | 0.96${}^{-}_{-}$ | 31.62${}^{-}_{-}$
$f_{s}$ | 0.04${}^{+0.04}_{-}$ | 0.04${}^{+0.04}_{-}$ | 0.03${}^{+0.04}_{-}$ | 0.03${}^{+0.04}_{-0.03}$
Ccha | 1* | 1* | 1* | 1*
L$\rm{}_{2-10\,keV}$ |  |  |  | 3.98${}^{+0.38}_{-0.35}$ $\times$ 1043
L$\rm{}_{15-55\,keV}$ |  |  |  | 5.01${}^{+0.48}_{-0.44}$ $\times$ 1043

Notes: Same as Table 2.
cstat/dof: Chandra data only.

Table 8: ESO 549$-$50

Model | MYTorus | MYTorus | MYTorus | borus02
---|---|---|---|---
| (Coupled) | (Decoupled Face-on) | (Decoupled Edge-on) |
cstat/dof | 22/13 | 21/13 | 22/23 | 21/23
$\Gamma$ | 1.81${}^{+0.25}_{-0.14}$ | 1.86${}^{+0.23}_{-0.15}$ | 1.81${}^{+0.18}_{-0.10}$ | 1.91${}^{+0.02}_{-0.02}$
$N_{H,eq}$ | 0.27${}^{-}_{-0.05}$ | … | … | …
norm $10^{-2}$ | 0.10${}^{+0.09}_{-0.04}$ | 0.10${}^{+0.10}_{-0.04}$ | 0.10${}^{+0.09}_{-0.03}$ | 0.10${}^{+0.10}_{-0.02}$
cf,Tor | … | … | … | 0.35${}^{+0.05}_{-0.05}$
cos($\theta_{obs}$) | 0.01${}^{+0.49}_{-}$ | … | … | 0.95${}^{-}_{-0.77}$
$N_{H,Z}$ | … | 0.25${}^{+0.07}_{-0.04}$ | 0.26${}^{+0.14}_{-0.06}$ | 0.26${}^{+0.08}_{-0.06}$
$N_{H,S}$ | … | 1.6${}^{-}_{-1.59}$ | 0.50${}^{-}_{-}$ | 14.13${}^{-}_{-}$
$f_{s}$ | 0.002${}^{+0.004}_{-}$ | 0.001* | 0.002* | 0
Ccha | 1* | 1* | 1* | 1*
L$\rm{}_{2-10\,keV}$ |  |  |  | 3.98${}^{+0.70}_{-0.59}$ $\times$ 1042
L$\rm{}_{15-55\,keV}$ |  |  |  | 3.72${}^{+0.36}_{-0.33}$ $\times$ 1042

Notes: Same as Table 7.

Table 9: IRAS 11058$-$1131

Model | MYTorus | MYTorus | MYTorus | borus02
---|---|---|---|---
| (Coupled) | (Decoupled Face-on) | (Decoupled Edge-on) |
cstat/dof | 11/6 | 11/6 | 11/6 | 11/6
$\Gamma$ | 1.41${}^{+0.61}_{-}$ | 1.45${}^{+0.25}_{-}$ | 1.41${}^{+0.40}_{-}$ | 1.45${}^{+0.35}_{-}$
$N_{H,eq}$ | 10.00${}^{-}_{-}$ | … | … | …
norm $10^{-2}$ | 0.20${}^{+3.30}_{-0.20}$ | 0.04${}^{+0.04}_{-0.03}$ | 0.04${}^{+0.12}_{-0.02}$ | 0.04${}^{+0.16}_{-0.02}$
cf,Tor | … | … | … | 0.60${}^{-}_{-}$
cos($\theta_{obs}$) | 0.15${}^{+0.35}_{-}$ | … | … | 0.05*
$N_{H,Z}$ | … | 2.60${}^{-}_{-1.93}$ | 0.94${}^{-}_{-0.93}$ | 0.81${}^{+0.84}_{-0.74}$
$N_{H,S}$ | … | 9.04${}^{-}_{-6.88}$ | 8.75${}^{-}_{-}$ | 7.41${}^{-}_{-}$
$f_{s}$ | 0.003${}^{+0.099}_{-0.003}$ | 0.02${}^{+0.03}_{-0.01}$ | 0.02${}^{-}_{-0.02}$ | 0.03${}^{-}_{-}$
Ccha | 1.13${}^{+5.27}_{-1.02}$ | 0.88${}^{+0.91}_{-0.87}$ | 0.92${}^{-}_{-0.91}$ | 0.70${}^{+5.30}_{-0.69}$
L$\rm{}_{2-10\,keV}$ |  |  |  | 1.55${}^{+1.47}_{-1.06}$ $\times$ 1043
L$\rm{}_{15-55\,keV}$ |  |  |  | 3.16${}^{+0.31}_{-0.28}$ $\times$ 1043

Notes: Same as Table 7.
BAT cross-norm fixed at 1.

Table 10: MCG $+$08-33-046

Model | pileup
---|---
cstat/dof | 86/77
$\Gamma$ | 2.05
$N_{H,eq}$ | 0.02
norm $10^{-2}$ | 0.32
cf,Tor | …
cos($\theta_{obs}$) | …
$N_{H,Z}$ | …
$N_{H,S}$ | …
$f_{s}$ | …
Ccha | 1*
L$\rm{}_{2-10\,keV}$ | 4.90${}^{+0.47}_{-0.43}$ $\times$ 1042
L$\rm{}_{15-55\,keV}$ | 3.55${}^{+0.17}_{-0.16}$ $\times$ 1042

Notes: Same as Table 7.

Table 11: IRAS 12571$+$7643

Model | MYTorus | MYTorus | MYTorus | borus02
---|---|---|---|---
| (Coupled) | (Decoupled Face-on) | (Decoupled Edge-on) |
cstat/dof | 44/30 | 44/30 | 43/30 | 41/30
$\Gamma$ | 1.69${}^{+0.11}_{-0.11}$ | 1.71${}^{+0.12}_{-0.10}$ | 1.75${}^{+0.13}_{-0.14}$ | 1.61${}^{+0.18}_{-0.07}$
$N_{H,eq}$ | 0.17${}^{+0.45}_{-0.03}$ | … | … | …
norm $10^{-2}$ | 0.07${}^{+0.02}_{-0.01}$ | 0.08${}^{+0.01}_{-0.01}$ | 0.07${}^{+0.03}_{-0.02}$ | 0.05${}^{+0.02}_{-0.01}$
cf,Tor | … | … | … | 0.15${}^{-}_{-}$
cos($\theta_{obs}$) | 0.0${}^{+0.5}_{-}$ | … | … | 0.90${}^{-}_{-}$
$N_{H,Z}$ | … | 0.18${}^{+0.06}_{-0.03}$ | 0.17${}^{+0.05}_{-0.05}$ | 0.16${}^{+0.05}_{-0.03}$
$N_{H,S}$ | … | 0.02${}^{+0.44}_{-}$ | 0.90${}^{-}_{-}$ | 0.01${}^{-}_{-}$
$f_{s}$ | 0.01${}^{+0.01}_{-0.01}$ | 0.01${}^{+0.01}_{-0.01}$ | 0.01${}^{+0.02}_{-0.01}$ | 0.01${}^{+0.01}_{-}$
Ccha | 1* | 1* | 1* | 1*
L$\rm{}_{2-10\,keV}$ |  |  |  | 2.09${}^{+0.25}_{-0.27}$ $\times$ 1043
L$\rm{}_{15-55\,keV}$ |  |  |  | 3.63${}^{+0.17}_{-0.16}$ $\times$ 1043

Notes: Same as Table 7.

##  Appendix B Chandra Exposures

Figure 8: From top to bottom: the Chandra exposures for 2MASX
J02051994$-$0233055, 2MASX J04075215$-$6116126, 2MASX J08445829$+$3056386 in
the 1$-$7 keV range. Large green circles represent the BAT 95 % uncertainty
region while small green circles identify the correct counterpart of the BAT
source; red/magenta circles are for sources detected by Chandra and located
within/nearby the BAT 95 % uncertainty region, but which we determine are not
the counterparts of the BAT source (see the text for more details). Table 12:
BAT 95% Confidence Regions

Swift-BAT ID | Source Name | 95% Region
---|---|---
|  | Arcmin
J0205.2$-$0232 | 2MASX J02051994$-$0233055∗ | 2.76
J0402.6$-$2107 | ESO 549$-$50† | 4.49
J0407.8$-$6116 | 2MASX J04075215$-$6116126∗ | 3.40
J0844.8$+$3055 | 2MASX J08445829$+$3056386∗ | 2.95
J0901.8$-$6418 | ESO 090$-$IG 014∗ | 2.87
J1108.4$-$1148 | IRAS 11058$-$1131† | 4.73
J1111.0$+$0054 | 2MASX J11110059$-$0053347† | 4.65
J1258.4$+$7624 | IRAS 12571+7643† | 4.35
J1828.8$+$5021 | MCG $+$08-33-046† | 3.77

Notes:
$*$: From the 100-month BAT Catalog.
$\dagger$: From the 150-month BAT Catalog.

Figure 9: From top to bottom: the Chandra exposures for 2MASX
J11110059$-$0053347, ESO 549$-$50, IRAS 11058$-$1131 in the 1$-$7 keV range.
Large green circles represent the BAT 95 % uncertainty region while small
green circles identify the correct counterpart of the BAT source; red/magenta
circles are for sources detected by Chandra and located within/nearby the BAT
95 % uncertainty region, but which we determine are not the counterparts of
the BAT source (see the text for more details). Figure 10: From top to bottom:
the Chandra exposures for MCG $+$08-33-046, IRAS 12571$+$7643 in the 1$-$7 keV
range. Large green circles represent the BAT 95 % uncertainty region while
small green circles identify the correct counterpart of the BAT source;
red/magenta circles are for sources detected by Chandra and located
within/nearby the BAT 95 % uncertainty region, but which we determine are not
the counterparts of the BAT source (see the text for more details).

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