11,534 research outputs found
The structure of the X-ray absorber in Mrk 915 revealed by Swift
In this paper we present the results obtained with a monitoring programme (23
days long) performed with Swift-XRT on the local Seyfert galaxy Mrk 915. The
light-curve analysis shows a significant count rate variation (about a factor
of 2-3) on a time-scale of a few days, while the X-ray colours show a change in
the spectral curvature below 2 keV and the presence of two main spectral
states. From the spectral analysis we find that the observed variations can be
explained by the change of the intrinsic nuclear power (about a factor of 1.5)
coupled with a change of the properties of an ionized absorber. The quality of
the data prevents us from firmly establishing if the spectral variation is due
to a change in the ionization state and/or in the covering factor of the
absorbing medium. The latter scenario would imply a clumpy structure of the
ionized medium. By combining the information provided by the light curve and
the spectral analyses, we can derive some constraints on the location of the
absorber under the hypotheses of either homogeneous or clumpy medium. In both
cases, we find that the absorber should be located inside the outer edge of an
extended torus and, in particular, under the clumpy hypothesis, it should be
located near, or just outside, to the broad emission line region.Comment: 8 pages, 6 figures, 1 table. Accepted for publication on MNRA
XMM-Newton and NuSTAR joint observations of Mrk 915: a deep look into the X-ray properties
We report on the X-ray monitoring programme (covering slightly more than 11
days) carried out jointly by XMM-Newton and NuSTAR on the intermediate Seyfert
galaxy Mrk 915. The light curves extracted in different energy ranges show a
variation in intensity but not a significant change in spectral shape. The
X-ray spectra reveal the presence of a two-phase warm absorber: a fully
covering mildly ionized structure [log xi/(erg cm/s)~2.3, NH~1.3x10^21 cm-2]
and a partial covering (~90 per cent) lower ionized one [log xi/(erg cm/s)~0.6,
NH~2x10^22 cm-2]. A reflection component from distant matter is also present.
Finally, a high-column density (NH~1.5x10^23 cm-2) distribution of neutral
matter covering a small fraction of the central region is observed, almost
constant, in all observations. Main driver of the variations observed between
the datasets is a decrease in the intrinsic emission by a factor of ~1.5.
Slight variations in the partial covering ionized absorber are detected, while
the data are consistent with no variation of the total covering absorber. The
most likely interpretation of the present data locates this complex absorber
closer to the central source than the narrow line region, possibly in the broad
line region, in the innermost part of the torus, or in between. The neutral
obscurer may either be part of this same stratified structure or associated
with the walls of the torus, grazed by (and partially intercepting) the line of
sight.Comment: 14 pages, 10 figures, 4 tables. Accepted for publication in MNRA
Mining the XRT archive to probe the X-ray absorber structure in the AGN population
One of the key ingredients of the Unified Model of Active Galactic Nuclei
(AGN) is the presence of a torus-like optically thick medium composed by dust
and gas around the putative supermassive black hole. However, the structure,
size and composition of this circumnuclear medium are still matter of debate.
To this end, the search for column density variations through X-ray monitoring
on different timescales (months, weeks and few days) is fundamental to
constrain size, kinematics and location of the X-ray absorber(s). Here we
describe our project of mining the Swift-XRT archive to assemble a sample of
AGN with extreme column density variability and determining the physical
properties of the X-ray absorber(s). We also present the results obtained from
a daily-weekly Swift-XRT follow-up monitoring recently performed on one of the
most interesting new candidates for variability discovered so far, Mrk 915.Comment: 6 pages, 3 figures. To appear in Proceedings of Science for the
"Swift: 10 years of Discovery" meeting, held in Rome (2-5 December 2014
Anode supported microtubular solid oxide fuel cells running on methane
Trabajo presentado al "III Iberian Symposium on Hydrogen, Fuel Cells and Advanced Batteries" celebrado en Zaragoza (España) del 27 al 30 de Junio de 2011.We would like to thank grants MAT2009-14324-C0.2-01 and CIT-120000-2007-50 financed by the Spanish Government and Feder program of the European Community for funding project. M. A. Laguna-Bercero would also like to thank the JAEprogram (CSIC) for financial support.Peer Reviewe
Effective absorbing column density in the gamma-ray burst afterglow X-ray spectra
We investigate the scaling relation between the observed amount of absorption
in the X-ray spectra of Gamma Ray Burst (GRB) afterglows and the absorber
redshift. Through dedicated numerical simulations of an ideal instrument, we
establish that this dependence has a power law shape with index 2.4. However,
for real instruments, this value depends on their low energy cut-off, spectral
resolution and on the detector spectral response in general. We thus provide
appropriate scaling laws for specific instruments. Finally, we discuss the
possibility to measure the absorber redshift from X-ray data alone. We find
that 10^5-10^6 counts in the 0.3-10 keV band are needed to constrain the
redshift with 10% accuracy. As a test case we discuss the XMM-Newton
observation of GRB 090618 at z=0.54. We are able to recover the correct
redshift of this burst with the expected accuracy.Comment: MNRAS accepted. 6 figures. 3 table
Multi-wavelength observations of IGR J17544-2619 from quiescence to outburst
In this paper we report on a long multi-wavelength observational campaign of
the supergiant fast X-ray transient prototype IGR J17544-2619. A 150 ks-long
observation was carried out simultaneously with XMM-Newton and NuSTAR, catching
the source in an initial faint X-ray state and then undergoing a bright X-ray
outburst lasting about 7 ks. We studied the spectral variability during
outburst and quiescence by using a thermal and bulk Comptonization model that
is typically adopted to describe the X-ray spectral energy distribution of
young pulsars in high mass X-ray binaries. Although the statistics of the
collected X-ray data were relatively high we could neither confirm the presence
of a cyclotron line in the broad-band spectrum of the source (0.5-40 keV), nor
detect any of the previously reported tentative detection of the source spin
period. The monitoring carried out with Swift/XRT during the same orbit of the
system observed by XMM-Newton and NuSTAR revealed that the source remained in a
low emission state for most of the time, in agreement with the known property
of all supergiant fast X-ray transients being significantly sub-luminous
compared to other supergiant X-ray binaries. Optical and infrared observations
were carried out for a total of a few thousands of seconds during the
quiescence state of the source detected by XMM-Newton and NuSTAR. The measured
optical and infrared magnitudes were slightly lower than previous values
reported in the literature, but compatible with the known micro-variability of
supergiant stars. UV observations obtained with the UVOT telescope on-board
Swift did not reveal significant changes in the magnitude of the source in this
energy domain compared to previously reported values.Comment: Accepted for publication on A&A. V2: few typos correcte
The natural history of ankylosing spondylitis in the 21st century
Ankylosing spondylitis (AS) is a chronic inflammatory disease that affects the axial skeleton and evolves in stiffnes followed by ankylosis and disability. However, it may be difficult to exactly establish the natural history of the disease and the influence of risk factors of progression, since most patients are treated with various pharmacologic or non-pharmacologic agents, which may potentially influence the natural progression of the disease. In this context, we report here a very interesting case of a 40 year old man, presented to our outpatient clinic, 28 years after the onset of AS. Previously for personal reasons, did not choose not to undergo any treatment. This case allows us to evaluate the natural radiological progression of the disease and the influence of predictive risk factors
Swift J201424.9+152930: discovery of a new deeply eclipsing binary with 491 s and 3.4 h modulations
We report on the discovery of a new X-ray pulsator, Swift J201424.9+152930
(Sw J2014). Owing to its X-ray modulation at 491 s, it was discovered in a
systematic search for coherent signals in the archival data of the Swift X-ray
Telescope. To investigate the nature of Sw J2014, we performed multi-wavelength
follow-up observations with space-borne (Swift and XMM-Newton) and ground-based
(the 1.5-m Loiano Telescope and the 3.6-m Telescopio Nazionale Galileo)
instruments. The X-ray spectrum of Sw J2014 can be described by a hard and
highly absorbed power law. The optical observations made it possible to single
out the optical counterpart to this source, which displays several variable
emission lines and total eclipses lasting ~20 min. Total eclipses of similar
length were observed also in X-rays. The study of the eclipses, allowed us to
infer a second periodicity of 3.44 h, which we interpret as the orbital period
of a close binary system. We also found that the period has not significantly
changed over a ~7 yr timespan. Based on the timing signatures of Sw J2014, and
its optical and X-ray spectral properties, we suggest that it is a close binary
hosting an accreting magnetic white dwarf. The system is therefore a
cataclysmic variable of the intermediate polar type and one of the very few
showing deep eclipses.Comment: 12 pages, 8 figures, 5 tables; minor changes to match the final MNRAS
versio
A complete sample of bright Swift short Gamma-Ray Bursts
We present a carefully selected sample of short gamma-ray bursts (SGRBs)
observed by the Swift satellite up to June 2013. Inspired by the criteria we
used to build a similar sample of bright long GRBs (the BAT6 sample), we
selected SGRBs with favorable observing conditions for the redshift
determination on ground, ending up with a sample of 36 events, almost half of
which with a redshift measure. The redshift completeness increases up to about
70% (with an average redshift value of z = 0.85) by restricting to those events
that are bright in the 15-150 keV Swift Burst Alert Telescope energy band. Such
flux-limited sample minimizes any redshift-related selection effects, and can
provide a robust base for the study of the energetics, redshift distribution
and environment of the Swift bright population of SGRBs. For all the events of
the sample we derived the prompt and afterglow emission in both the observer
and (when possible) rest frame and tested the consistency with the correlations
valid for long GRBs. The redshift and intrinsic X-ray absorbing column density
distributions we obtain are consistent with the scenario of SGRBs originated by
the coalescence of compact objects in primordial binaries, with a possible
minor contribution (~10%-25%) of binaries formed by dynamical capture (or
experiencing large natal kicks). This sample is expected to significantly
increase with further years of Swift activity.Comment: 17 pages, 8 figures, 7 tables. Accepted for publication in MNRA
Evidence for a clumpy disc-wind in the star forming Seyfert\,2 galaxy MCG--03--58--007
We report the results of a detailed analysis of a deep simultaneous \textit{XMM-Newton & NuSTAR} observation of the nearby () and
bright () starburst-AGN
Seyfert\,2 system: MCG--03--58--007. From the broadband fitting we show that
most of the obscuration needs to be modeled with a toroidal type reprocessor
such as \texttt{MYTorus} \citep{MurphyYaqoob09}. Nonetheless the signature of a
powerful disc-wind is still apparent at higher energies and the observed rapid
short-term X-ray spectral variability is more likely caused by a variable zone
of highly ionized fast wind rather than by a neutral clumpy medium. We also
detect X-ray emission from larger scale gas as seen from the presence of
several soft narrow emission lines in the RGS, originating from a contribution
of a weak star forming activity together with a dominant photoionized component
from the AGN.Comment: 16 pages, 9 figures, accepted for publication in MNRA
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