130 research outputs found
The properties of the clumpy torus and BLR in the polar-scattered Seyfert 1 galaxy ESO 323-G77 through X-ray absorption variability
We report results from multi-epoch X-ray observations of the polar-scattered
Seyfert 1 galaxy ESO 323-G77. The source exhibits remarkable spectral
variability from months to years timescales. The observed spectral variability
is entirely due to variations of the column density of a neutral absorber
towards the intrinsic nuclear continuum. The column density is generally
Compton-thin ranging from a few times 10 cm to a few times
10 cm. However, one observation reveals a Compton-thick state
with column density of the order of 1.5 10 cm. The
observed variability offers a rare opportunity to study the properties of the
X-ray absorber(s) in an active galaxy. We identify variable X-ray absorption
from two different components, namely (i) a clumpy torus whose individual
clumps have a density of 1.7 10 cm and an average
column density of 4 10 cm, and (ii) the broad
line region (BLR), comprising individual clouds with density of 0.1-8
10 cm and column density of 10-10 cm. The
derived properties of the clumpy torus can also be used to estimate the torus
half-opening angle, which is of the order of 47 . We also confirm the
previously reported detection of two highly ionized warm absorbers with outflow
velocities of 1000-4000 km s. The observed outflow velocities are
consistent with the Keplerian/escape velocity at the BLR. Hence, the warm
absorbers may be tentatively identified with the warm/hot inter-cloud medium
which ensures that the BLR clouds are in pressure equilibrium with their
surroundings. The BLR line-emitting clouds may well be the cold, dense clumps
of this outflow, whose warm/hot phase is likely more homogeneous, as suggested
by the lack of strong variability of the warm absorber(s) properties during our
monitoring.Comment: 15 pages, 4 tables, and 9 figures. Accepted for publication in MNRA
Accurate classification of 75 counterparts of objects detected in the 54 month Palermo Swift/BAT hard X-ray catalogue
Through an optical campaign performed at 4 telescopes located in the northern
and the southern hemispheres, we have obtained optical spectroscopy for 75
counterparts of unclassified or poorly studied hard X-ray emitting objects
detected with Swift/BAT and listed in the 54 month Palermo BAT catalogue. All
these objects have also observations taken with Swift/XRT, ROSAT or Chandra
satellites which allowed us to reduce the high energy error box and pinpoint
the most likely optical counterpart/s. We find that 69 sources in our sample
are Active Galactic Nuclei (AGNs); of them, 35 are classified as type 1 (with
broad and narrow emission lines), 33 are classified as type 2 (with only narrow
emission lines) and one is an high redshift QSO; the remaining 6 objects are
galactic cataclysmic variables (CVs). Among type 1 AGNs, 32 are objects of
intermediate Seyfert type (1.2-1.9) and one is Narrow Line Seyfert 1 galaxy;
for 29 out of 35 type 1 AGNs, we have been able to estimate the central black
hole mass and the Eddington ratio. Among type 2 AGNs, two display optical
features typical of the LINER class, 3 are classified as transition objects, 1
is a starburst galaxy and 2 are instead X-ray bright, optically normal
galaxies. All galaxies classified in this work are relatively nearby objects
(0.006 - 0.213) except for one at redshift 1.137.Comment: 19 pages, 5 figures, 6 tables, accepted for publications on Astronomy
and Astrophysics, main journal. arXiv admin note: text overlap with
arXiv:1206.509
XMM-Newton view of galaxy pairs: activation of quiescent black holes?
We report on XMM-Newton observations of three nearby galaxy pairs,
AM0707-273, AM1211-465, and AM2040-674. All six galaxies were previously
classified as HII galaxies based on optical and IR spectroscopic analysis. All
galaxies were detected with XMM-Newton and each member was isolated and
analyzed independently. The X-ray spectra reveal strong evidence of AGN
activity in the NE member of AM1211-465 pair. We measured a luminosity of
1.94(+0.11/-0.15)x10^42 erg/s in the 2-10 keV band and the presence of a
neutral FeK_alpha line with a confidence level of 98.8%. The high nH value,
2.2+/-0.2x10^22 cm^-2, would explain the misclassification of the source.
Marginal evidence of AGN nature was found in the X-ray spectra of AM1211-465SW
and AM0707-273E. The X-ray emission of the three remaining galaxies can be
explained by starburst activity.Comment: Accepted for publication in A&
Fossil group origins - VI. Global X-ray scaling relations of fossil galaxy clusters
We present the first pointed X-ray observations of 10 candidate fossil galaxy
groups and clusters. With these Suzaku observations, we determine global
temperatures and bolometric X-ray luminosities of the intracluster medium (ICM)
out to for six systems in our sample. The remaining four systems show
signs of significant contamination from non-ICM sources. For the six objects
with successfully determined properties, we measure global
temperatures in the range ,
bolometric X-ray luminosities of , and estimate masses,
as derived from , of .
Fossil cluster scaling relations are constructed for a sample that combines our
Suzaku observed fossils with fossils in the literature. Using measurements of
global X-ray luminosity, temperature, optical luminosity, and velocity
dispersion, scaling relations for the fossil sample are then compared with a
control sample of non-fossil systems. We find the fits of our fossil cluster
scaling relations are consistent with the relations for normal groups and
clusters, indicating fossil clusters have global ICM X-ray properties similar
to those of comparable mass non-fossil systems.Comment: 17 pages, 7 figures, 8 tables. Accepted for publication in MNRA
Detection of blueshifted emission and absorption and a relativistic Iron line in the X-ray spectrum of ESO 323-G077
We report on the X-ray observation of the Seyfert 1 ESO323-G077 performed
with XMM-Newton. The spectra show a complex spectrum with conspicuous
absorption and emission features. The continuum emission can be modelled with a
power law with an index of 1.99+/-0.02 in the whole XMM-Newton energy band,
marginally consistent with typical values of Type-I objects. An absorption
component with an uncommonly high equivalent Hydrogen column,
n_H=5.82(+0.12/-0.11)x10^22 cm-2, is affecting the soft part of the spectrum.
Additionally, two warm absorption components are also present. The lower
ionised one has an ionisation parameter of Log(U)=2.14(+0.06/-0.07) and an
outflowing velocity of v=3200(+600/-200) km/s. Two absorption lines located at
~6.7 and ~7.0 keV can be modelled with the highly ionised absorber. The
ionisation parameter and outflowing velocity of the gas measured are
Log(U)=3.26(+0.19/-0.15) and v=1700(+600/-400) km/s, respectively. Four
emission lines were also detected in the soft energy band. The most likely
explanation for these emission lines is that they are associated with an
outflowing gas with a velocity of ~2000 km/s. The data suggest that the same
gas which is causing the absorption could also being responsible of these
emission features. Finally, the spectrum shows the presence of a relativistic
iron emission line likely originated in the accretion disc of a Kerr BH with an
inclination of ~25 deg. We propose a model to explain the observed X-ray
properties which invokes the presence of a two-phase outflow with cone-like
structure and a velocity of the order of 2,000-4,000 km/s. The inner layer of
the cone would be less ionised, or even neutral, than the outer layer. The
inclination angle would be lower than the opening angle of the outflowing cone.Comment: 11 pages, accepted in MNRA
Engulfing a radio pulsar: the case of PSR J1023+0038
The binary millisecond radio pulsar PSR J1023+0038 has been recently the
subject of multiwavelength monitoring campaigns which revealed that an
accretion disc has formed around the neutron star (since 2013 June). We present
here the results of X-ray and UV observations carried out by the Swift
satellite between 2013 October and 2014 May, and of optical and NIR
observations performed with the REM telescope, the Liverpool Telescope, the
2.1-m telescope at the San Pedro M\'artir Observatory and the 1.52-m telescope
at the Loiano observing station. The X-ray spectrum is well described by an
absorbed power law, which is softer than the previous quiescent epoch (up to
2013 June). The strong correlation between the X-ray and the UV emissions
indicates that the same mechanism should be responsible for part of the
emission in these bands. Optical and infrared photometric observations show
that the companion star is strongly irradiated. Double-peaked emission lines in
the optical spectra provide compelling evidence for the presence of an outer
accretion disc too. The spectral energy distribution from IR to X-rays is well
modelled if the contributions from the companion, the disc and the intra-binary
shock emission are all considered. Our extensive data set can be interpreted in
terms of an engulfed radio pulsar: the radio pulsar is still active, but
undetectable in the radio band due to a large amount of ionized material
surrounding the compact object. X-rays and gamma-rays are produced in an
intra-binary shock front between the relativistic pulsar wind and matter from
the companion and an outer accretion disc. The intense spin-down power
irradiates the disc and the companion star, accounting for the UV and optical
emissions.Comment: 11 pages, 8 figures, 5 tables; accepted for publication on MNRA
Refining the associations of the Fermi Large Area Telescope Source Catalogs
The Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) was released
in February 2010 and the Fermi-LAT 2-Year Source Catalog (2FGL) appeared in
April 2012, based on data from 24 months of operation. Since their releases,
many follow up observations of unidentified gamma-ray sources (UGSs) were
performed and new procedures to associate gamma-ray sources with potential
counterparts at other wavelengths were developed. Here we review and
characterize all the associations as published in the 1FGL and 2FGL catalog on
the basis of multifrequency archival observations. In particular we located 177
spectra for the low-energy counterparts that were not listed in the previous
Fermi catalogs, and in addition we present new spectroscopic observations of 8
gamma-ray blazar candidates. Based on our investigations, we introduce a new
counterpart category of "candidate associations" and propose a refined
classification for the candidate low-energy counterparts of the Fermi sources.
We compare the 1FGL-assigned counterparts with those listed in the 2FGL to
determine which unassociated sources became associated in later releases of the
Fermi catalogs. We also search for potential counterparts to all the remaining
unassociated Fermi sources. Finally, we prepare a refined and merged list of
all the associations of the 1FGL plus 2FGL catalogs that includes 2219 unique
Fermi objects. This is the most comprehensive and systematic study of all the
associations collected for the gamma-ray sources available to date. We conclude
that 80% of the Fermi sources have at least one known plausible gamma-ray
emitter within their positional uncertainty regions.Comment: 26 pages, 24 figures, 7 tables, ApJS accepted for publication
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