115 research outputs found
A receding torus model for the Iwasawa-Taniguchi effect for Compton-thick AGN
Recently, Boorman et al. (2018) reported on the discovery of the
Iwasawa-Taniguchi (I-T) effect (a.k.a. X-ray Baldwin effect) for Compton-thick
AGN. They measured a decrease of the 6.4 keV iron line equivalent width with
the 12mu luminosity, assumed as a proxy for the intrinsic X-ray luminosity,
which in Compton-thick AGN is not directly observable. One of the most popular
explanations of the classic I-T effect is the so-called receding torus model,
i.e. the decrease of the covering factor of the molecular `torus' with X-ray
luminosity. In this paper we show that an I-T effect for Compton-thick AGN is
indeed expected in the receding torus model, assuming that the torus is
funnelling the primary X-ray luminosity which is then scattered in a `hot
mirror'. We found that the observed relation is well reproduced provided that
the typical column density of the `hot mirror' is about 7.5x10^{22} cm^{-2}.Comment: 4 pages, 2 figures. Accepted for publication in MNRA
The circumnuclear X-ray reflectors in NGC 1068 and the Circinus Galaxy
The ASCA and BeppoSAX spectra of the Circinus Galaxy and NGC 1068 are
analysed and compared with photoionization models based on cloudy. In the case
of Circinus, a single, mildly ionized reflector can account for the line
spectrum, while in NGC 1068 at least three different reflectors (with different
ionization states) are needed. We suggest that the reflector in Circinus, and
the low ionized one in NGC1068 are the inner and visible part of the material
responsible for the X-ray absorption. With this assumption, we estimate for the
inner radius of the absorber a value of 0.2 pc for Circinus and of a few
parsecs for NGC 1068.Comment: accepted for publication in MNRA
A Detection of an X-ray Wind and an Ionized Disk in the Chandra HETGS Observation of the Seyfert 2 Galaxy IRAS 18325-5926
We analyze the \textit{Chandra} High Energy Transmission Grating Spectrometer
(HETGS) observation of the Seyfert AGN IRAS\,18325-5926. We detect a
~km~s blueshifted ionized absorber in the X-ray
spectrum, with photoionization parameter and
hydrogen column density ~cm. The absorber may be a
photoionized wind originating in the obscuring torus/global covering around the
black hole or outer edge of the accretion disk. The estimated mass outflow rate
suggests that the supermassive black hole in IRAS\,18325-5926 may significantly
affect the large-scale environment of the host galaxy, unless the solid angle
subtended by the outflow or the gas filling factor is small. A second warm
absorber may be needed to explain the absorption features in the vicinity of
the iron K edge, although insufficient counts in the data beyond ~keV make
it difficult to assess the nature of the second absorber. Most plausible is a
high ionization ( to ), high column density (~cm) absorber with to ~km~s,
although these parameters are not well constrained. We also examine the broad
Fe K emission line in the spectrum, which is likely due to Fe XXV in a highly
ionized accretion disk inclined at , consistent with the
\textit{XMM-Newton} EPIC observations of the emission line. Because we are able
to view both the obscuring gas and the accretion disk of IRAS\,18325-5926, the
surrounding gas of IRAS\,18325-5926 may be patchy or we are viewing the system
at an angle just grazing the obscuring torus.Comment: 28 pg, 5 tables, 6 figure
The role of molecular gas in the nuclear regions of IRAS 00183-7111. ALMA and X-ray investigations of an ultraluminous infrared galaxy
We present a multi-frequency study of the ultraluminous infrared galaxy
(ULIRG) IRAS 00183-7111 (z=0.327), selected from the Spoon diagnostic diagram
as a highly obscured active galactic nucleus (AGN) candidate. ALMA Cycle 0
millimetre and X-ray observations are used; the main aim is to verify at what
level the molecular gas, traced by the CO, may be responsible for the
obscuration observed at X-ray energies. Theory and observations both suggest
that galaxy-scale absorption may play a role in the AGN obscuration at
intermediate (i.e. Compton-thin) column densities. We derived a molecular gas
column density of cm from the ALMA
CO detection, while the best-fit column density of cold gas obtained
from X-ray spectral fitting is cm. The
two quantities suggest that the molecular gas may contribute only a fraction of
the AGN obscuration; however, the link between them is not straightforward. The
nuclear regions of IRAS 00183-7111 are likely stratified into different layers
of matter: one inner and highly ionized by the strong radiation field of the
AGN (as inferred from the high-ionization iron line found in the X-ray
spectra), and one outer and colder, extending more than 5~kpc from the nucleus
(as traced by the molecular gas observed with ALMA). The molecular gas regions
also give rise to a vigorous starburst with SFR M
yr. The complexity of this nuclear environment makes it difficult to
identify the origin of the AGN obscuration given the quality of the data
currently available. Higher resolution observations in the millimetre regime
are needed to deeply investigate this issue.Comment: 15 pages, 7 figures, 5 tables. Accepted for publication in A&
Peculiar objects towards 3FGL J0133.3+5930: an eclipsing Be star and an active galactic nucleus
Aims. We aim to contribute to the identification of unassociated gamma-ray
sources in the galactic plane in order to enlarge the currently known
population of gamma-ray binaries and related systems, such as radio emitting
X-ray binaries and microquasars. These objects are currently regarded as
excellent test beds for the understanding of high energy phenomena in stellar
systems. Methods. Potential targets of study are selected based on
cross-identification of the 3rd Fermi Large Area Telescope catalogue with
historical catalogues of luminous stars often found as optical counterparts in
known cases. Follow-up observations and analysis of multi-wavelength archival
data are later used to seek further proofs of association beyond the simple
positional agreement. Results. Current results enable us to present here the
case of the Fermi source 3FGL J0133.3+5930 where two peculiar objects have been
discovered inside its region of uncertainty. One of them is the star TYC
3683-985-1 (LS I +59 79) whose eclipsing binary nature is reported in this
work. The other one is the X-ray source SWIFT J0132.9+5932, that we found to be
a likely low-power Active Galactic Nucleus at z = 0:1143 \pm 0:0002. If this
second object is of blazar type, it could easily account for the observed
gamma-ray photon flux. However, this is not confirmed at present, thus
rendering still open the star system TYC 3683-985-1 as an alternative
counterpart candidate to the Fermi source.Comment: 8 pages; 10 figures; accepted for publication in Astronomy &
Astrophysic
Elliptical Galaxy in the Making: The Dual Active Galactic Nuclei and Metal-enriched Halo of Mrk 273
A systematic analysis of the X-ray emission from the nearby ultraluminous
infrared galaxy Mrk 273 was carried out by combining new 200 ksec Chandra data
with archived 44 ksec data. The active galactic nucleus (AGN) associated with
the Southwest nucleus is confirmed by the new data, and a secondary hard X-ray
(4-8 keV) point source is detected, coincident with the Northeast nucleus at a
projected distance of 0.75 kpc from the Southwest nucleus. The hard X-ray
spectrum of the Northeast nucleus is consistent with a heavily absorbed AGN,
making Mrk 273 another example of a dual AGN in a nearby galaxy merger.
Significant 1-3 keV emission is found along the ionization cones and outflowing
gas detected in a previous study. The data also map the giant X-ray nebula
south of the host galaxy with unprecedented detail. This nebula extends on a
scale of 40 kpc 40 kpc, and is not closely related to the
well-known tidal tail seen in the optical. The X-ray emission of the nebula is
best described by a single-temperature gas model, with a temperature of
7 million K and a super-solar /Fe ratio. Further analysis suggests that
the southern nebula has most likely been heated and enriched by multiple
galactic outflows generated by the AGN and/or circumnuclear starburst in the
past, on a time scale of 0.1 Gyr, similar to the merger event itself.Comment: 25 pages, 22 figures, 4 tables, accepted for publication in the
Astrophysical Journa
X-Ray bright optically faint active galactic nuclei in the Subaru Hyper Suprime-Cam wide survey
We construct a sample of X-ray bright optically faint active galactic nuclei
by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source
catalogs. 53 X-ray sources satisfying i band magnitude fainter than 23.5 mag
and X-ray counts with EPIC-PN detector larger than 70 are selected from 9.1
deg^2, and their spectral energy distributions (SEDs) and X-ray spectra are
analyzed. 44 objects with an X-ray to i-band flux ratio F_X/F_i>10 are
classified as extreme X-ray-to-optical flux sources. SEDs of 48 among 53 are
represented by templates of type 2 AGNs or starforming galaxies and show
signature of stellar emission from host galaxies in the optical in the source
rest frame. Infrared/optical SEDs indicate significant contribution of emission
from dust to infrared fluxes and that the central AGN is dust obscured.
Photometric redshifts determined from the SEDs are in the range of 0.6-2.5.
X-ray spectra are fitted by an absorbed power law model, and the intrinsic
absorption column densities are modest (best-fit log N_H = 20.5-23.5 cm^-2 in
most cases). The absorption corrected X-ray luminosities are in the range of
6x10^42 - 2x10^45 erg s^-1. 20 objects are classified as type 2 quasars based
on X-ray luminsosity and N_H. The optical faintness is explained by a
combination of redshifts (mostly z>1.0), strong dust extinction, and in part a
large ratio of dust/gas.Comment: 25 pages, 14 figures, 5 tables, accepted for publication in PAS
The Hard X-Ray Luminosity Function of High-Redshift () Active Galactic Nuclei
We present the hard-band () X-ray luminosity function
(HXLF) of band selected AGN at high redshift. We have
assembled a sample of 141 AGN at from X-ray surveys of different
size and depth, in order to sample different regions in the plane.
The HXLF is fitted in the range with standard
analytical evolutionary models through a maximum likelihood procedure. The
evolution of the HXLF is well described by a pure density evolution, with the
AGN space density declining by a factor of from to 5. A
luminosity-dependent density evolution model which, normally, best represents
the HXLF evolution at lower redshift, is also consistent with the data, but a
larger sample of low-luminosity (), high-redshift AGN is
necessary to constrain this model. We also estimated the intrinsic fraction of
AGN obscured by a column density to be ,
with no strong dependence on luminosity. This fraction is higher than the value
in the Local Universe, suggesting an evolution of the luminous
() obscured AGN fraction from
to .Comment: MNRAS, Accepted 2014 September 23. Received 2014 September 10; in
original form 2014 August 5; 19 pages, 11 figures, 5 table
The XMM-Newton view of Mrk3 and IXO30
We present the analysis of the XMM-Newton EPIC pn spectrum of the Seyfert 2
galaxy, Mrk3. We confirm that the source is dominated by a pure Compton
reflection component and an iron K line, both produced as reflection
from a Compton-thick torus, likely responsible also for the large column
density which is pierced by the primary powerlaw only at high energies. A low
inclination angle and an iron underabundance, suggested by the amount of
reflection and the depth of the iron edge, are consistent with the iron
K line EW with respect to the Compton reflection component. Moreover,
the iron line width, if interpreted in terms of Doppler broadening due to the
Keplerian rotation of the torus, puts an estimate to the inner radius of the
latter, pc. Finally, two different photoionised
reflectors are needed to take into account a large number of soft X-ray
emission lines from N, O, Ne, Mg, Si, Fe L and the FeXXV emission line. RGS
spectra show that the soft X-ray spectrum is dominated by emission lines, while
the underlying continuum is best fitted by an unabsorbed powerlaw with the same
photon index of the primary continuum, produced as reflection by a photoionised
material with a column density of a few cm. We also present
the first X-ray spectrum of ROSAT source IXO30, which shows a huge iron line
and is well represented either by an absorbed powerlaw or bremsstrahlung
emission. Its spectral properties point to a likely identification in terms of
a weak Galactic Cataclysmic Variable, but the lack of any optical counterpart
precludes excluding other possibilities, like an ULX at the distance of Mrk3.Comment: 11 pages, 8 figures, accepted for publication in MNRA
The X-ray variability of the Seyfert~1 galaxy MCG-6-30-15 from long ASCA and RXTE observations
We present an analysis of the long RXTE observation of the Seyfert~1 galaxy
MCG-6-30-15, taken in July 1997. Our results show that the behaviour is
complicated. We find clear evidence from colour ratios and direct spectral
fitting that changes to the intrinsic photon index are taking place. Spectral
hardening is evident during periods of diminished intensity; in particular, a
general trend for harder spectra is seen in the period following the hardest
RXTE flare. Flux-correlated studies further show that the 3-10 keV photon index
steepens while that in the 10-20 keV band, flattens with flux. The largest
changes come from the spectral index below 10keV; however, changes in the
intrinsic power law slope, and reflection both contribute in varying degrees to
the overall spectral variability. We find that the iron line flux is consistent
with being constant over large time intervals on the order of days (although
the ASCA and RXTE spectra show that changes on shorter time
intervals of order < 10ks), and equivalent width which anticorrelates with the
continuum flux, and reflection fraction. Flux-correlated studies point at
possible ionization signatures, while detailed spectral analysis of short time
intervals surrounding flare events hint tentatively at observed spectral
responses to the flare. We present a simple model for partial ionization where
the bulk of the variability comes from within 6r_g. Temporal analysis further
provides evidence for possible time (< 1000s) and phase (phi~0.6 rad) lags.
Finally, we report an apparent break in the power density spectrum (~ 4-5 x
10^{-6}Hz) and a possible 33 hr period. Estimates for the mass of the black
hole in MCG-6-30-15 are discussed in the context of spectral and temporal
findings.Comment: 19 pages, 38 figures total (19 figure captions), accepted for
publication in MNRAS July 200
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