422 research outputs found
The NuSTAR View of the Seyfert 2 Galaxy NGC 4388
We present analysis of NuSTAR X-ray observations in the 3-79 keV energy band
of the Seyfert 2 galaxy NGC 4388, taken in 2013. The broadband sensitivity of
NuSTAR, covering the Fe K line and Compton reflection hump, enables
tight constraints to be placed on reflection features in AGN X-ray spectra,
thereby providing insight into the geometry of the circumnuclear material. In
this observation, we found the X-ray spectrum of NGC 4388 to be well described
by a moderately absorbed power law with non-relativistic reflection. We fit the
spectrum with phenomenological reflection models and a physical torus model,
and find the source to be absorbed by Compton-thin material (N cm) with a very weak Compton reflection hump
(R 0.09) and an exceptionally large Fe K line (EW eV) for a source with weak or no reflection. Calculations
using a thin-shell approximation for the expected Fe K EW indicate that
an Fe K line originating from Compton-thin material presents a possible
explanation.Comment: 5 pages, 2 figures. Accepted for publication in Ap
The multi-layer variable absorbers in NGC 1365 revealed by XMM-Newton and <i>NuSTAR</i>
Between 2012 July and 2013 February, NuSTAR and XMM-Newton performed four long-look joint observations of the type 1.8 Seyfert, NGC 1365. We have analyzed the variable absorption seen in these observations in order to characterize the geometry of the absorbing material. Two of the observations caught NGC 1365 in an unusually low absorption state, revealing complexity in the multi-layer absorber that had previously been hidden. We find the need for three distinct zones of neutral absorption in addition to the two zones of ionized absorption and the Compton-thick torus previously seen in this source. The most prominent absorber is likely associated with broad-line region clouds with column densities of around approximately 10 (sup 23) per square centimeter and a highly clumpy nature as evidenced by an occultation event in 2013 February. We also find evidence of a patchy absorber with a variable column around approximately 10 (sup 22) per square centimeter and a line-of-sight covering fraction of 0.3-0.9, which responds directly to the intrinsic source flux, possibly due to a wind geometry. A full-covering, constant absorber with a low column density of approximately 1 by 10 (sup 22) per square centimeter is also present, though the location of this low density haze is unknown
Inferring Compton-thick AGN candidates at z>2 with Chandra using the >8 keV restframe spectral curvature
To fully understand cosmic black hole growth we need to constrain the
population of heavily obscured active galactic nuclei (AGN) at the peak of
cosmic black hole growth (1-3). Sources with obscuring column densities
higher than atoms , called Compton-thick
(CT) AGN, can be identified by excess X-ray emission at 20-30 keV, called
the "Compton hump". We apply the recently developed Spectral Curvature (SC)
method to high-redshift AGN (2<z<5) detected with Chandra. This method
parametrizes the characteristic "Compton hump" feature cosmologically
redshifted into the X-ray band at observed energies <10 keV. We find good
agreement in CT AGN found using the SC method and bright sources fit using
their full spectrum with X-ray spectroscopy. In the Chandra deep field south,
we measure a CT fraction of (3/17) for sources with
observed luminosity erg . In the
Cosmological evolution survey (COSMOS), we find an observed CT fraction of
(40/272) or when corrected for
the survey sensitivity. When comparing to low redshift AGN with similar X-ray
luminosities, our results imply the CT AGN fraction is consistent with having
no redshift evolution. Finally, we provide SC equations that can be used to
find high-redshift CT AGN (z>1) for current (XMM-Newton) and future (eROSITA
and ATHENA) X-ray missions.Comment: 10 pages, 8 figure
Investigating the evolution of the dual AGN system ESO~509-IG066
We analyze the evolution of the dual AGN in ESO 509-IG066, a galaxy pair
located at z=0.034 whose nuclei are separated by 11 kpc. Previous observations
with XMM-Newton on this dual AGN found evidence for two moderately obscured
( cm) X-ray luminous ( erg/s) nuclear
sources. We present an analysis of subsequent Chandra, NuSTAR and Swift/XRT
observations that show one source has dropped in flux by a factor of 10 between
2004 and 2011, which could be explained by either an increase in the absorbing
column or an intrinsic fading of the central engine possibly due to a decrease
in mass accretion. Both of these scenarios are predicted by galaxy merger
simulations. The source which has dropped in flux is not detected by NuSTAR,
which argues against absorption, unless it is extreme. However, new Keck/LRIS
optical spectroscopy reveals a previously unreported broad H-alpha line which
is highly unlikely to be visible under the extreme absorption scenario. We
therefore conclude that the black hole in this nucleus has undergone a dramatic
drop in accretion rate. From AO-assisted near-infrared integral-field
spectroscopy of the other nucleus, we find evidence that the galaxy merger is
having a direct effect on the kinematics of the gas close to the nucleus of the
galaxy, providing a direct observational link between the galaxy merger and the
mass accretion rate on to the black hole.Comment: Accepted for publication in Ap
The 2-79 keV X-ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton and Chandra: a Fully Compton-Thick AGN
The Circinus galaxy is one of the nearest obscured AGN, making it an ideal
target for detailed study. Combining archival Chandra and XMM-Newton data with
new NuSTAR observations, we model the 2-79 keV spectrum to constrain the
primary AGN continuum and to derive physical parameters for the obscuring
material. Chandra's high angular resolution allows a separation of nuclear and
off-nuclear galactic emission. In the off-nuclear diffuse emission we find
signatures of strong cold reflection, including high equivalent-width neutral
Fe lines. This Compton-scattered off-nuclear emission amounts to 18% of the
nuclear flux in the Fe line region, but becomes comparable to the nuclear
emission above 30 keV. The new analysis no longer supports a prominent
transmitted AGN component in the observed band. We find that the nuclear
spectrum is consistent with Compton-scattering by an optically-thick torus,
where the intrinsic spectrum is a powerlaw of photon index ,
the torus has an equatorial column density of cm and the intrinsic AGN keV luminosity is
erg/s. These values place Circinus along the same
relations as unobscured AGN in accretion rate-vs- and -vs-
phase space. NuSTAR's high sensitivity and low background allow us to study the
short time-scale variability of Circinus at X-ray energies above 10 keV for the
first time. The lack of detected variability favors a Compton-thick absorber,
in line with the the spectral fitting results.Comment: Accepted for publication in Ap
Broadband Observations of the Compton-thick Nucleus of NGC 3393
We present new NuSTAR and Chandra observations of NGC 3393, a galaxy reported
to host the smallest separation dual AGN resolved in the X-rays. While past
results suggested a 150 pc separation dual AGN, three times deeper Chandra
imaging, combined with adaptive optics and radio imaging suggest a single,
heavily obscured, radio-bright AGN. Using VLA and VLBA data, we find an AGN
with a two-sided jet rather than a dual AGN and that the hard X-ray, UV,
optical, NIR, and radio emission are all from a single point source with a
radius <0.2". We find that the previously reported dual AGN is most likely a
spurious detection resulting from the low number of X-ray counts (<160) at 6-7
keV and Gaussian smoothing of the data on scales much smaller than the PSF
(0.25" vs. 0.80" FWHM). We show that statistical noise in a single Chandra PSF
generates spurious dual peaks of the same separation (0.550.07" vs. 0.6")
and flux ratio (399% vs. 32% of counts) as the purported dual AGN. With
NuSTAR, we measure a Compton-thick source (NH=
cm) with a large torus half-opening angle, {\theta}=79 which we
postulate results from feedback from strong radio jets. This AGN shows a 2-10
keV intrinsic to observed flux ratio of 150. Using simulations, we find that
even the deepest Chandra observations would severely underestimate the
intrinsic luminosity of NGC 3393 above z>0.2, but would detect an unobscured
AGN of this luminosity out to high redshift (z=5).Comment: Accepted for publication in ApJ. 15 Figures and 4 table
The nature of the torus in the heavily obscured AGN Markarian 3: an X-ray study
In this paper we report the results of an X-ray monitoring campaign on the
heavily obscured Seyfert galaxy Markarian 3 carried out between the fall of
2014 and the spring of 2015 with NuSTAR, Suzaku and XMM-Newton. The hard X-ray
spectrum of Markarian 3 is variable on all the time scales probed by our
campaign, down to a few days. The observed continuum variability is due to an
intrinsically variable primary continuum seen in transmission through a large,
but still Compton-thin column density (N_H~0.8-1.110 cm).
If arranged in a spherical-toroidal geometry, the Compton scattering matter has
an opening angle ~66 degrees and is seen at a grazing angle through its upper
rim (inclination angle ~70 degrees). We report a possible occultation event
during the 2014 campaign. If the torus is constituted by a system of clouds
sharing the same column density, this event allows us to constrain their number
(175) and individual column density, [~(4.91.5)10
cm]. The comparison of IR and X-ray spectroscopic results with
state-of-the art "torus" models suggests that at least two thirds of the X-ray
obscuring gas volume might be located within the dust sublimation radius. We
report also the discovery of an ionized absorber, characterised by variable
resonant absorption lines due to He- and H-like iron. This discovery lends
support to the idea that moderate column density absorbers could be due to
clouds evaporated at the outer surface of the torus, possibly accelerated by
the radiation pressure due to the central AGN emission leaking through the
patchy absorber.Comment: Accepted for publication in MNRAS, 17 pages, 11 figures, 5 table
X-ray bolometric corrections for Compton-thick active galactic nuclei
We present X-ray bolometric correction factors, (), for Compton-thick (CT) active galactic nuclei (AGN) with the aim
of testing AGN torus models, probing orientation effects, and estimating the
bolometric output of the most obscured AGN. We adopt bolometric luminosities,
, from literature infrared (IR) torus modeling and compile published
intrinsic 2--10 keV X-ray luminosities, , from X-ray torus modeling of
NuSTAR data. Our sample consists of 10 local CT AGN where both of these
estimates are available. We test for systematic differences in
values produced when using two widely used IR torus models and two widely used
X-ray torus models, finding consistency within the uncertainties. We find that
the mean of our sample in the range
erg/s is log
with an intrinsic scatter of dex, and that our derived
values are consistent with previously established relationships between
and and and Eddington ratio. We
investigate if is dependent on by comparing our results on
CT AGN to published results on less-obscured AGN, finding no significant
dependence. Since many of our sample are megamaser AGN, known to be viewed
edge-on, and furthermore under the assumptions of AGN unification whereby
unobscured AGN are viewed face-on, our result implies that the X-ray emitting
corona is not strongly anisotropic. Finally, we present values
for CT AGN identified in X-ray surveys as a function of their observed ,
where an estimate of their intrinsic is not available, and redshift,
useful for estimating the bolometric output of the most obscured AGN across
cosmic time.Comment: Accepted for publication in Ap
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