1,753 research outputs found
A systematic analysis of X-ray afterglows of gamma-ray burst observed by XMM-Newton
This work is part of a systematic re-analysis program of all the data of
Gamma-Ray Burst (GRB) X-ray afterglows observed so far, in order to constrain
the GRB models. We present here a systematic analysis of those afterglows
observed by XMM-Newton between January 2000 and March 2004. This dataset
includes GRB 011211 and GRB 030329. We have obtained spectra, light curves and
colors for these afterglows. In this paper we focus on the continuum spectral
and temporal behavior. We compare these values with the theoretical ones
expected from the fireball model. We derive constraints about the burst
environment (absorption, density profile) and put constraints on their beaming
angle.Comment: 7 pages, 2 figures, COSPAR proceeding accepted for publication in
Advances in Space Researc
Broad band X-ray spectral properties of Gamma-ray bursts with BeppoSAX
In about one year, five gamma-ray bursts were simultaneously observed with
the Wide Field Cameras and Gamma Ray Burst Monitor aboard the BeppoSAX
satellite. From some of them X-ray afterglow emission has been clearly detected
with the same satellite. In order to understand how GRB emission is related to
the X-ray afterglow, we are performing a systematic study of the spectral
properties of these events. We report here preliminary results of this study.Comment: 5 pages, 3 figures. To appear in the Proceedings of the 4th
Huntsville Gamma-ray Burst Symposiu
Gamma-ray burst observations with new generation imaging atmospheric Cerenkov Telescopes in the FERMI era
After the launch and successful beginning of operations of the FERMI
satellite, the topics related to high-energy observations of gamma-ray bursts
have obtained a considerable attention by the scientific community.
Undoubtedly, the diagnostic power of high-energy observations in constraining
the emission processes and the physical conditions of gamma-ray burst is
relevant. We briefly discuss how gamma-ray burst observations with ground-based
imaging array Cerenkov telescopes, in the GeV-TeV range, can compete and
cooperate with FERMI observations, in the MeV-GeV range, to allow researchers
to obtain a more detailed and complete picture of the prompt and afterglow
phases of gamma-ray bursts.Comment: 9 pages, two figures. Proceeding for the 6th "Science with the New
Generation of High Energy Gamma-Ray Experiments" worksho
Theoretical interpretation of the X-ray properties of GRB960720
BeppoSAX observations of the single pulse burst GRB960720 have allowed a
detailed study of its X-ray properties: pulse width in different energy bands,
spectral evolution from 2 to 700 keV, etc. We show that the early (0-5s) X-ray
emission and the gamma-rays are well explained by internal shocks in a
relativistic wind while the late (5-20s) X-ray emission could come from the
reverse shock generated in the wind when it interacts with the external medium.
The results for a medium of uniform density are compared to the observations.Comment: 2 pages, 2 figures. Submitted to A&A, Proc. of Rome Conf. on
Gamma-ray Bursts in the Afterglow Er
The true redshift distribution of Pre-SWIFT gamma-ray bursts
SWIFT bursts appear to be more distant than previous bursts. We present the
Boer & Gendre relation that link redshift and afterglow luminosities. Taking
advantage of the XMM-Newton, Chandra and BeppoSAX catalogs, and using this
relation, we have investigated the redshift distribution of GRBs. We find that
XMM burst sources with unknown redshift appear to be more distant than those
with a known redshift. We propose that this effect may be due to a selection
effect of pre-SWIFT optical observations.Comment: Proceedings of the "Gamma Ray Bursts in the Swift Era" conference, 6
pages, 5 color figure
GRB 000418: A Hidden Jet Revealed?
We report on optical, near-infrared and centimeter radio observations of
GRB000418 which allow us to follow the evolution of the afterglow from 2 to 200
days after the gamma-ray burst. In modeling these broad-band data, we find that
an isotropic explosion in a constant density medium is unable to simultaneously
fit both the radio and optical data. However, a jet-like outflow with an
opening angle of 10-20 degress provides a good description of the data. The
evidence in favor of a jet interpretation is based on the behavior of the radio
light curves, since the expected jet break is masked at optical wavelengths by
the light of the host galaxy. We also find evidence for extinction, presumably
arising from within the host galaxy, with A(V)=0.4 mag, and host flux densities
of F_R=1.1 uJy and F_K=1.7 uJy. These values supercede previous work on this
burst due to the availability of a broad-band data set allowing a global
fitting approach. A model in which the GRB explodes into a wind-stratified
circumburst medium cannot be ruled out by these data. However, in examining a
sample of other bursts (e.g. GRB990510, GRB000301C) we favor the jet
interpretation for GRB000418.Comment: ApJ, submitte
Theory of Gamma-Ray Burst Emission in Light of BSAX Results
We briefly discuss the theoretical implications of recent detections of
gamma-ray bursts (GRBs) by BSAX. Relativistic shock wave theories of fireball
expansion are challenged by the wealth of X-ray, optical and radio data
obtained after the discovery of the first X-ray GRB afterglow. BSAX data
contribute to address several issues concerning the initial and afterglow GRB
emission. The observations also raise many questions that are still unsolved.
The synchrotron shock model is in very good agreement with time-resolved
broad-band spectra (2-500 keV) for the majority of GRBs detected by BSAX.Comment: 8 pages, LATEX text plus two postscript figures included. To appear
in the Proceedings of the Accademia dei Lincei Symposium: "The Active X-ray
Sky: Results from Beppo-SAX and Rossi-XTE", Nuclear Physics B Proceedings
Supplement, eds. L. Scarsi et a
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