62 research outputs found
Broadband X-ray spectral analysis of the Seyfert 1 galaxy GRS 1734-292
We discuss the broadband X-ray spectrum of GRS 1734-292 obtained from
non-simultaneous XMM-Newton and NuSTAR observations, performed in 2009 and
2014, respectively. GRS1734-292 is a Seyfert 1 galaxy, located near the
Galactic plane at . The NuSTAR spectrum ( keV) is dominated by
a primary power-law continuum with and a high-energy
cutoff keV, one of the lowest measured by NuSTAR in a
Seyfert galaxy. Comptonization models show a temperature of the coronal plasma
of keV and an optical depth, assuming a slab
geometry, or a similar temperature and
assuming a spherical geometry. The 2009 XMM-Newton
spectrum is well described by a flatter intrinsic continuum
() and one absorption line due to Fe\textsc{XXV}
K produced by a warm absorber. Both data sets show a modest iron
K emission line at keV and the associated Compton reflection, due
to reprocessing from neutral circumnuclear material
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
Scattered X-rays in Obscured Active Galactic Nuclei and their Implications for Geometrical Structure and Evolution
We construct a new sample of 32 obscured active galactic nuclei (AGNs)
selected from the Second XMM-Newton Serendipitous Source Catalogue to
investigate their multiwavelength properties in relation to the "scattering
fraction", the ratio of the soft X-ray flux to the absorption-corrected direct
emission. The sample covers a broad range of the scattering fraction
(0.1%-10%). A quarter of the 32 AGNs have a very low scattering fraction
(smaller than 0.5%), which suggests that they are buried in a geometrically
thick torus with a very small opening angle. We investigate correlations
between the scattering fraction and multiwavelength properties. We find that
AGNs with a small scattering fraction tend to have low [O III]lambda5007/X-ray
luminosity ratios. This result agrees with the expectation that the extent of
the narrow-line region is small because of the small opening angle of the
torus. There is no significant correlation between scattering fraction and
far-infrared luminosity. This implies that a scale height of the torus is not
primarily determined by starburst activity. We also compare scattering fraction
with black hole mass or Eddington ratio and find a weak anti-correlation
between the Eddington ratio and scattering fraction. This implies that more
rapidly growing supermassive black holes tend to have thicker tori.Comment: 13 pages, 10 figures, accepted for publication in Ap
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
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
NuSTAR Spectroscopy of Multi-Component X-ray Reflection from NGC 1068
We report on observations of NGC1068 with NuSTAR, which provide the best
constraints to date on its ~keV spectral shape. We find no strong
variability over the past two decades, consistent with its Compton-thick AGN
classification. The combined NuSTAR, Chandra, XMM-Newton, and Swift-BAT
spectral dataset offers new insights into the complex reflected emission. The
critical combination of the high signal-to-noise NuSTAR data and a spatial
decomposition with Chandra allow us to break several model degeneracies and
greatly aid physical interpretation. When modeled as a monolithic (i.e., a
single N_H) reflector, none of the common Compton-reflection models are able to
match the neutral fluorescence lines and broad spectral shape of the Compton
reflection. A multi-component reflector with three distinct column densities
(e.g., N_H~1.5e23, 5e24, and 1e25 cm^{-2}) provides a more reasonable fit to
the spectral lines and Compton hump, with near-solar Fe abundances. In this
model, the higher N_H components provide the bulk of the Compton hump flux
while the lower N_H component produces much of the line emission, effectively
decoupling two key features of Compton reflection. We note that ~30% of the
neutral Fe Kalpha line flux arises from >2" (~140 pc), implying that a
significant fraction of the <10 keV reflected component arises from regions
well outside of a parsec-scale torus. These results likely have ramifications
for the interpretation of poorer signal-to-noise observations and/or more
distant objects [Abridged].Comment: Submitted to ApJ; 23 pages (ApJ format); 11 figures and 3 tables;
Comments welcomed
Broad-band X-ray spectral analysis of the Seyfert 1 galaxy GRS 1734-292
We discuss the broad-band X-ray spectrum of GRS 1734â292 obtained from non-simultaneous XMMâNewton and NuSTAR (Nuclear Spectroscopic Telescope Array) observations, performed in 2009 and 2014, respectively. GRS1734â292 is a Seyfert 1 galaxy, located near the Galactic plane at z = 0.0214. The NuSTAR spectrum (3â80 keV) is dominated by a primary power-law continuum with Î = 1.65 ± 0.05 and a high-energy cut-off Ec=53+11â8 keV, one of the lowest measured by NuSTAR in a Seyfert galaxy. Comptonization models show a temperature of the coronal plasma of kTe=11.9+1.2â0.9 keV and an optical depth, assuming a slab geometry, Ï=2.98+0.16â0.19 or a similar temperature and Ï=6.7+0.3â0.4 assuming a spherical geometry. The 2009 XMMâNewton spectrum is well described by a flatter intrinsic continuum (â Î=1.47+0.07â0.03â ) and one absorption line due to Fe XXV Kα produced by a warm absorber. Both data sets show a modest iron Kα emission line at 6.4 keV and the associated Compton reflection, due to reprocessing from neutral circumnuclear material
Mid-Infrared Properties of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. I. Emission-Line Diagnostics
We compare mid-infrared emission-line properties, from high-resolution
Spitzer spectra of a hard X-ray (14 -- 195 keV) selected sample of nearby (z <
0.05) AGN detected by the Burst Alert Telescope (BAT) aboard Swift. The
luminosity distribution for the mid-infrared emission-lines, [O IV] 25.89
micron, [Ne II] 12.81 micron, [Ne III] 15.56 micron and [Ne V] 14.32/24.32
micron, and hard X-ray continuum show no differences between Seyfert 1 and
Seyfert 2 populations, however six newly discovered BAT AGNs are under-luminous
in [O IV], most likely the result of dust extinction in the host galaxy. The
overall tightness of the mid-infrared correlations and BAT fluxes and
luminosities suggests that the emission lines primarily arise in gas ionized by
the AGN. We also compare the mid-infrared emission-lines in the BAT AGNs with
those from published studies of ULIRGs, PG QSOs, star-forming galaxies and
LINERs. We find that the BAT AGN sample fall into a distinctive region when
comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] ratios. These line
ratios are lower in sources that have been previously classified in the
mid-infrared/optical as AGN than those found for the BAT AGN, suggesting that,
in our X-ray selected sample, the AGN represents the main contribution to the
observed line emission. These ratios represent a new emission line diagnostic
for distinguishing between AGN and star forming galaxies.Comment: 54 pages, 9 Figures. Accepted for publication in The Astrophysical
Journal
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