514 research outputs found
Monitoring RXTE Observations of Markarian 348: the origin of the column density variations
We analyze 37 RXTE observations of the type 2 Seyfert galaxy Mrk348 obtained
during a period of 14 months. We confirm the spectral variability previous
reported by Smith et al., in the sense that thecolumn density decreases by a
factor of ~3 as the count rate increases. Column density variations could
possibly originate either due to the random drift of clouds within the
absorption screen, or due to photoionization processes. Our modeling of the
observed variations implies that the first scenario is more likely. These
clouds should lie in a distance of >2 light years from the source, having a
diameter of a few light days and a density of >10^7 cm^(-3), hence probably
residing outside the Broad Line Region.Comment: 6 pages, 3 figures, to appear in MNRA
RXTE monitoring observations of Markarian 3
We present Rossi X-ray Timing Explorer, monitoring observations of the
Seyfert 2 galaxy Markarian 3 spanning a 200 day period during which time the
source flux varied by a factor in the 4-20 keV bandpass. In broad
agreement with earlier Ginga results, the average spectrum can be represented
in terms of a simple spectral model consisting of a very hard power-law
continuum () modified below keV by a high
absorbing column ( \cunits) together with a high
equivalent width Fe-K emission feature at 6.4 keV. The abnormally flat spectral
index is probably the signature of a strong reflection component and we
consider two models incorporating such emission. In the first the reflected
signal suffers the same absorption as the intrinsic continuum, whereas in the
second the reflection is treated as an unabsorbed spectral component. In the
former case, we require a very strong reflection signal () in order to
match the data; in addition variability of both the intrinsic power-law and the
reflection component is required. The unabsorbed reflection model requires a
somewhat higher line-of-sight column density to the nuclear source ( \cunits), but in this case the reflected signal remains constant
whilst the level of the intrinsic continuum varies. The latter description is
consistent with the reflection originating from the illuminated far inner wall
of a molecular torus, the nearside of which screens our direct view of the
central continuum source.Comment: 7 pages, submitted to the MNRA
ASCA observations of type-2 Seyfert Galaxies. III. Orientation and X-ray Absorption
We discuss the spectral properties of a sample of type-2 Seyfert galaxies
based upon the analysis of \asca data. In this paper we consider the sources
for which the X-ray spectra appear to be dominated by the nuclear continuum,
transmitted through a large column of absorbing material. We find that both
Seyfert-2 galaxies and NELGs show iron K line profiles indicative of
reprocessing of nuclear X-rays in a face-on accretion disk. Such line profiles
are also observed in Seyfert-1 galaxies. This result is contrary to unification
models, which would predict the inner regions of Seyfert-2 galaxies to be
observed edge-on. This raises some questions as to the orientation of the
circumnuclear absorber. If the observed differences between Seyfert type-1 and
type-2 galaxies, and NELGs are not due to differences in the orientation of the
absorbing material, then we suggest that differences in dust composition and
grain size, and in the density of the circumnuclear gas could be of primary
importance.Comment: 28 pages, 3 figures. LaTeX with encapsulated postscript. To appear in
the Astrophysical Journa
High-Energy Spectral Complexity from Thermal Gradients in Black Hole Atmospheres
We show that Compton scattering of soft photons with energies near 100 eV in
thermally stratified black-hole accretion plasmas with temperatures in the
range 100 keV - 1 MeV can give rise to an X-ray spectral hardening near 10 keV.
This could produce the hardening observed in the X-ray spectra of black holes,
which is generally attributed to reflection or partial covering of the incident
continuum source by cold optically thick matter. In addition, we show that the
presence of very hot (kT=1 MeV) cores in plasmas leads to spectra exibiting
high energy tails similar to those observed from Galactic black-hole
candidates.Comment: 11 pages, uuencoded gziped postscript, ApJ Letters in pres
XMM-Newton observation of the brightest X-ray flare detected so far from SgrA*
We report the high S/N observation on October 3, 2002 with XMM-Newton of the
brightest X-ray flare detected so far from SgrA* with a duration shorter than
one hour (~ 2.7 ks). The light curve is almost symmetrical with respect to the
peak flare, and no significant difference between the soft and hard X-ray range
is detected. The overall flare spectrum is well represented by an absorbed
power-law with a soft photon spectral index of Gamma=2.5+/-0.3, and a peak 2-10
keV luminosity of 3.6 (+0.3-0.4) x 10^35 erg/s, i.e. a factor 160 higher than
the Sgr A* quiescent value. No significant spectral change during the flare is
observed. This X-ray flare is very different from other bright flares reported
so far: it is much brighter and softer. The present accurate determination of
the flare characteristics challenge the current interpretation of the physical
processes occuring inside the very close environment of SgrA* by bringing very
strong constraints for the theoretical flare models.Comment: Accepted for publication in A&A Letters. 4 pages, 2 figures, 1 table
The X-ray spectra and spectral variability of intermediate type Seyfert galaxies: ASCA observations of NGC 4388 and ESO 103-G35
The X-ray spectra of two intermediate type Seyfert galaxies are investigated
using ASCA observations separated by more than a year. Both NGC 4388 and ESO
103-G35 exhibit strong, narrow Fe K alpha line emission and absorption by cold
neutral gas with a column density ~ 10^23 cm^-2, characteristic of the X-ray
spectra of type 2 Seyfert galaxies. The power law continuum flux has changed by
a factor of 2 over a time-scale of ~ 2 years for both objects, declining in the
case of NGC 4388 and rising in ESO 103-G35. No variation was observed in the
equivalent width of the Fe K alpha line in the spectra of NGC 4388, implying
that the line flux declined with the continuum. We find that the strength of
the line cannot be accounted for by fluorescence in line-of-sight material with
the measured column density unless a `leaky-absorber' model of the type favored
for IRAS 04575-7537 is employed. The equivalent width of the Fe K alpha
emission line is seen to decrease between the observations of ESO 103-G35 while
the continuum flux increased. The 1996 observation of ESO 103-G35 can also be
fitted with an absorption edge at 7.4 0.2 keV due to partially ionized
iron, and when an ionized absorber model is fitted to the data it is found that
the equivalent column of neutral hydrogen rises to 3.5 x 10^23 cm^-2. The Fe K
alpha line flux can be accounted by fluorescence in this material alone and
this model is also a good representation of the 1988 and 1991 Ginga
observations. There is then no requirement for a reflection component in the
ASCA spectra of ESO 103-G35 or NGC 4388.Comment: 45 pages, 5 tables, 11 figures. Accepted for publication in the
Astrophysical Journa
Anti-cytokine therapy in fibrosing alveolitis: where are we now?
Idiopathic pulmonary fibrosis (IPF) is a condition that has a poor prognosis, with a median survival of 4-5 years irrespective of treatment. Ziesche et al (N Engl J Med 1999, 341: 1264-1269) describe an open randomised trial of 18 patients with IPF, unresponsive to corticosteroid treatment at high dose. Nine patients were treated with continued corticosteroid and nine with prednisolone plus interferon-γ 1b (IFN-γ). Significant benefits in physiological parameters are reported in the IFN-γ-treated group. An analysis of lung tissue by reverse-transcriptase-mediated polymerase chain reaction showed corresponding decreases in the transcription of transforming growth factor-β1 and connective tissue growth factor. This is the first report of treatment showing efficacy in this disease, albeit in a very preliminary study, but the data should be viewed with caution. This study is discussed in the context of other published studies of treatment for IPF and the scientific rationale on which it was based
The nature of the X-ray halo of the plerion G21.5-0.9 unveiled by XMM-Newton and Chandra
The nature of the radio-quiet X-ray halo around the plerionic SNR G21.5-0.9
is under debate. On the basis of spatial and spectral analysis of a large
Chandra and XMM-Newton dataset of this source, we have developed a
self-consistent scenario which explains all the observational features. We
found that the halo is composed by diffuse extended emission due to dust
scattering of X-rays from the plerion, by a bright limb which traces particle
acceleration in the fast forward shock of the remnant, and by a bright spot
(the ``North Spur'') which may be a knot of ejecta in adiabatic expansion. By
applying a model of interaction between the PWN, the SNR and supernova
environment, we argue that G21.5-0.9 progenitor may be of Type IIP or Ib/Ic,
and that the remnant may be young (200-1000 yr).Comment: 11 pages, 10 figures, accepted by A&A, also avalaible at
http://www.astropa.unipa.it/Library/OAPA_preprints/fb2870.ps.g
The Galactic Plane at faint X-ray fluxes - I: Properties and characteristics of the X-ray source population
We investigate the serendipitous X-ray source population revealed in
XMM-Newton observations targeted in the Galactic Plane within the region
315<l<45 and |b|<2.5 deg. Our study focuses on a sample of 2204 X-ray sources
at intermediate to faint fluxes, which were detected in a total of 116 XMM
fields and are listed in the 2XMMi catalogue. We characterise each source as
spectrally soft or hard on the basis of whether the bulk of the recorded counts
have energies below or above 2 keV and find that the sample divides roughly
equally (56%:44%) into these soft and hard categories. The X-ray spectral form
underlying the soft sources may be represented as either a power-law continuum
with Gamma~2.5 or a thermal spectrum with kT~0.5 keV, with N_H ranging from
10^{20-22} cm^{-2}. For the hard sources, a significantly harder continuum form
is likely, i.e., Gamma~1 with N_H=10^{22-24} cm^{-2}. For ~50% of the hard
sources, the inferred column density is commensurate with the total Galactic
line-of-sight value; many of these sources will be located at significant
distances across the Galaxy implying a hard band luminosity L_X>10^{32} erg/s,
whereas some will be extragalactic interlopers. >90% of the soft sources have
potential NIR (2MASS and/or UKIDSS) counterparts inside their error circles,
consistent with the dominant soft X-ray source population being relatively
nearby coronally-active stars. These stellar counterparts are generally
brighter than J=16, a brightness cutoff which corresponds to the saturation of
the X-ray coronal emission at L_X=10^{-3} L_{bol}. In contrast, the success
rate in finding likely IR counterparts to the hard X-ray sample is no more than
~15% down to J=16 and ~25% down to J=20, set against a rapidly rising chance
coincidence rate. The make-up of the hard X-ray source population, in terms of
the known classes of accreting and non-accreting systems, remains uncertain.Comment: 17 pages, 17 figures, accepted for publication in MNRA
XMM-Newton observation of the Lockman Hole; I. The X-ray Data
We report on the first deep X-ray survey with the XMM-Newton observatory
during the performance verification phase. The field of the Lockman Hole, one
of the best studied sky areas over a very wide range of wavelengths, has been
observed. A total of ~100 ksec good exposure time has been accumulated.
Combining the images of the European Photon Imaging Camera (EPIC) detectors we
reach a flux limit of 0.31, 1.4 and 2.4 X 10^{-15} erg cm^{-2} s^{-1},
respectively in the 0.5-2, 2-10, and 5-10 keV band. Within an off-axis angle of
10 arcmin we detect 148, 112 and 61 sources, respectively. The log(N)-log(S)
relation in the three bands is compared with previous results. In particular in
the 5-10 keV band these observations present the deepest X-ray survey ever,
about a factor 20 more sensitive than the previous BeppoSAX observations. Using
X-ray spectral diagnostics and the set of previously known, spectroscopically
identified ROSAT sources in the field, the new sources can be classified.
XMM-Newton detects a significant number (~40%) of X-ray sources with hard,
probably intrinsically absorbed X-ray spectra, confirming a prediction of the
population synthesis models for the X-ray background.Comment: 6 pages, based on the new A&A style file (included), to be published
in A&A 365 (2001, special XMM issue), one page contains color image
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