385 research outputs found
Spectacular X-ray tails, intracluster star formation and ULXs in A3627
We present the discovery of spectacular double X-ray tails associated with
ESO137-001 and a possibly heated X-ray tail associated with ESO137-002, both
late-type galaxies in the closest rich cluster Abell 3627. A deep Chandra
observation of ESO137-001 allows us for the first time to examine the spatial
and spectral properties of such X-ray tails in detail. Besides the known bright
tail that extends to ~ 80 kpc from ESO137-001, a fainter and narrower secondary
tail with a similar length was surprisingly revealed. There is little
temperature variation along both tails. We also identified six X-ray point
sources as candidates of intracluster ULXs with L(0.3-10 keV) of up to
2.5x10^40 erg s^-1. Gemini spectra of intracluster HII regions downstream of
ESO137-001 are also presented, as well as the velocity map of these HII regions
that shows the imprint of ESO137-001's disk rotation. For the first time, we
unambiguously know that active star formation can happen in the cold ISM
stripped by ICM ram pressure and it may contribute a significant amount of the
intracluster light. We also report the discovery of a 40 kpc X-ray tail of
another late-type galaxy in A3627, ESO137-002. Its X-ray tail seems hot, ~ 2
keV (compared to ~ 0.8 keV for ESO137-001's tails). We conclude that the high
pressure environment around these two galaxies is important for their bright
X-ray tails and the intracluster star formation.Comment: ApJ in press, January 2010, v708, only several minor word changes,
emulateapj5.sty, 24 pages, 11 color + 5 B/W figures (figure quality degraded)
and 4 tables. The abstract has been abbreviated. A high-resolution PDF is
available at: http://www.astro.virginia.edu/~ms4ar/eso137_p3.pd
INTEGRAL observations of Sco X-1: evidence for Comptonization up to 200 keV
We have analyzed a long-term database for Sco X-1 obtained with the telescope
IBIS onboard the INTEGRAL satellite in order to study the hard X-ray behavior
of Sco X-1 from 20 up to 200 keV. Besides the data used for producing of the
INTEGRAL catalog of sources, this is the longest (412 ks) database of IBIS on
Sco X-1 up to date. The production of hard X-ray tails in low-mass X-ray
binaries is still a matter of debate. Since most of the fits to the high-energy
part of the spectra are done with powerlaw models, the physical mechanism for
the hard X-ray tail production is unclear. The purpose of this study is to
better constrain those possible mechanisms. Our main result shows a strong
correlation between the fluxes in the thermal and nonthermal part of Sco X-1
spectra. We thus suggest that Comptonization of lower energy photons is the
mechanism for producing hard X-ray tails in Sco X-1.Comment: 4 pages, 3 figures, 2 tables; officially accepted for publication (as
a Letter) by A&A in 2013 January 2
Cluster Mergers, Radio Halos and Hard X-ray Tails: A Statistical Magneto-Turbulent Model
There is now firm evidence that the ICM consists of a mixture of hot plasma,
magnetic fields and relativistic particles. The most important evidences for
non-thermal phenomena in galaxy clusters comes from the diffuse Mpc-scale
synchrotron radio emission (radio halos) observed in a growing number of
massive clusters (Feretti 2003) and from hard X-ray (HXR) excess emission
(detected in a few cases) which can be explained in terms of IC scattering of
relativistic electrons off the cosmic microwave background photons
(Fusco-Femiano et al. 2003). There are now growing evidences that giant radio
halos may be naturally accounted for by synchrotron emission from relativistic
electrons reaccelerated by some kind of turbulence generated in the cluster
volume during merger events (Brunetti 2003). With the aim to investigate the
connection between thermal and non-thermal properties of the ICM, we have
developed a statistical magneto-turbulent model which describes the evolution
of the thermal and non-thermal emission from clusters. We calculate the energy
and spectrum of the magnetosonic waves generated during cluster mergers, the
acceleration and evolution of relativistic electrons and thus the resulting
synchrotron and inverse Compton spectra. Here we give a brief description of
the main results, while a more detailed discussion will be presented in a
forthcoming paper. Einstein-De Sitter cosmology, km
, , is assumed.Comment: 3 pages, 2 figures. To appear in the proceedings of IAU Colloquium
195 - "Outskirts of galaxy clusters: intense life in the suburbs", Torino,
Italy, March 12-16, 200
A comprehensive analysis of Swift/XRT data: I. Apparent spectral evolution of GRB X-ray tails
An early steep decay component following the prompt GRBs is commonly observed
in {\em Swift} XRT light curves, which is regarded as the tail emission of the
prompt gamma-rays. Prompted by the observed strong spectral evolution in the
tails of GRBs 060218 and 060614, we present a systematic time-resolved spectral
analysis for the {\em Swift} GRB tails detected between 2005 February and 2007
January. We select a sample of 44 tails that are bright enough to perform
time-resolved spectral analyses. Among them 11 tails are smooth and without
superimposing significant flares, and their spectra have no significant
temporal evolution. We suggest that these tails are dominated by the curvature
effect of the prompt gamma-rays due to delay of propagation of photons from
large angles with respect to the line of sight . More interestingly, 33 tails
show clear hard-to-soft spectral evolution, with 16 of them being smooth tails
directly following the prompt GRBs,while the others being superimposed with
large flares. We focus on the 16 clean, smooth tails and consider three toy
models to interpret the spectral evolution. The curvature effect of a
structured jet and a model invoking superposition of the curvature effect tail
and a putative underlying soft emission component cannot explain all the data.
The third model, which invokes an evolving exponential spectrum, seems to
reproduce both the lightcurve and the spectral evolution of all the bursts,
including GRBs 060218 and 060614. More detailed physical models are called for
to understand the apparent evolution effect.Comment: 13 pages in emulateapj style,6 figures, 1 table, expanded version,
matched to published version, ApJ, 2007, in press. This is the first paper of
a series. Paper II see arXiv:0705.1373 (ApJ,2007, in press
Curvature Effect of a Non-Power-Law Spectrum and Spectral Evolution of GRB X-Ray Tails
The apparent spectral evolution observed in the steep decay phase of many GRB
early afterglows raises a great concern of the high-latitude "curvature effect"
interpretation of this phase. However, previous curvature effect models only
invoked a simple power law spectrum upon the cessation of the prompt internal
emission. We investigate a model that invokes the "curvature effect" of a more
general non-power-law spectrum and test this model with the Swift/XRT data of
some GRBs. We show that one can reproduce both the observed lightcurve and the
apparent spectral evolution of several GRBs using a model invoking a power-law
spectrum with an exponential cut off. GRB 050814 is presented as an example.Comment: 12 pages, 4 figures, 1 table, . Accepted for publication in ApJ
Letter
Hard X-ray tails and cyclotron features in X-ray pulsars
We review the physical processes occurring in the magnetosphere of accreting
X-ray pulsars, with emphasis on those processes that give rise to observable
effects in their high (E>10 keV) energy spectra. In the second part we compare
the empirical spectral laws used to fit the observed spectra with theoretical
models, at the light of the BeppoSAX results on the broad-band characterization
of the X-ray pulsar continuum, and the discovery of new (multiple) cyclotron
resonance features.Comment: Review talk given at the "X-ray Astronomy '99" Conferenc
New observations with the gamma ray imager SIGMA
Results from the use of the gamma ray telescope SIGMA are given. An identification and an extensive study was done of sources contributing to the emission of the Galactic center region above 30 keV. A strong line was observed at 480 keV from Nova Muscae, which may be interpreted as an annihilation line with a redshift due to the presence of a compact object. The soft x-ray tails observed by SIGMA in some transient sources already identified as soft x-ray transients might be a common characteristic of these objects and has to be explained. The unusual spectrum of NGC4151 with a break around 50 keV can characterize a particular state of this kind of object. If it is the case, it has interesting implications for the origin of the Cosmic Diffuse Background
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