7,154 research outputs found
Time Resolved GRB Spectroscopy
We present the main results of a study of time-resolved spectra of 43 intense
GRBs detected by BATSE. We considered the 4-parameter Band model and the
Optically Thin Synchrotron Shock model (OTSSM). We find that the large majority
of time-resolved spectra of GRBs are in remarkable agreement with the OTSSM.
However, about 15 % of initial GRB pulses show an apparent low-energy photon
suppression. This phenomenon indicates that complex radiative conditions
modifying optically thin emission may occur during the initial phases of some
GRBs.Comment: 5 pages, 3 figures, Paper presented at the 5th Huntsville Symposium,
Huntsville (Alabama) Oct. 199
The Statistics of the BATSE Spectral Features
The absence of a BATSE line detection in a gamma-ray burst spectrum during
the mission's first six years has led to a statistical analysis of the
occurrence of lines in the BATSE burst database; this statistical analysis will
still be relevant if lines are detected. We review our methodology, and present
new simulations of line detectability as a function of the line parameters. We
also discuss the calculation of the number of ``trials'' in the BATSE database,
which is necessary for our line detection criteria.Comment: 5 pages, 2 figures, AIPPROC LaTeX, to appear in "Gamma-Ray Bursts,
4th Huntsville Symposium," eds. C. Meegan, R. Preece and T. Koshu
Gamma Ray Bursts from the early Universe: predictions for present-day and future instruments
Long Gamma Ray Bursts (GRBs) constitute an important tool to study the
Universe near and beyond the epoch of reionization. We delineate here the
characteristics of an 'ideal' instrument for the search of GRBs at z>6-10. We
find that the detection of these objects requires soft band detectors with a
high sensitivity and moderately large FOV. In the light of these results, we
compare available and planned GRB missions, deriving conservative predictions
on the number of high-z GRBs detectable by these instruments along with the
maximum accessible redshift. We show that the Swift satellite will be able to
detect various GRBs at z>6, and likely at z>10 if the trigger threshold is
decreased by a factor of ~2. Furthermore, we find that INTEGRAL and GLAST are
not the best tool to detect bursts at z>6: the former being limited by the
small FOV, and the latter by its hard energy band and relatively low
sensitivity. Finally, future missions (SVOM, EDGE, but in particular EXIST)
will provide a good sample of GRBs at z>6 in a few years of operation.Comment: 6 pages, 2 figures, MNRAS in pres
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Evidence for clonal selection of gamma/delta T cells in response to a human pathogen.
T cells bearing gamma/delta antigen receptors comprise a resident population of intraepithelial lymphocytes in organs such as skin, gut, and lungs, where they are strategically located to contribute to the initial defense against infection. An important unsolved question about antigen-driven gamma/delta T cell responses regards the breadth of their T cell receptor (TCR) repertoire, since many specific epithelial compartments in mice display limited diversity. We have examined the diversity of TCR delta gene expression among human gamma/delta T cells from skin lesions induced by intradermal challenge with Mycobacterium leprae. We show that the vast majority of gamma/delta cells from M. leprae lesions use either V delta 1-J delta 1 or V delta 2-J delta 1 gene rearrangements and, within a given region of the lesion, display limited junctional diversity. This contrasts markedly with the extensive diversity of gamma/delta T cells from peripheral blood of these same individuals, as well as skin from normal donors. These results indicate that the gamma/delta response to M. leprae involves the selection of a limited number of clones from among a diverse repertoire, probably in response to specific mycobacterial and/or host antigens
Influence of the Earth on the background and the sensitivity of the GRM and ECLAIRs instruments aboard the Chinese-French mission SVOM
SVOM (Space-based multi-band astronomical Variable Object Monitor) is a
future Chinese-French satellite mission which is dedicated to Gamma-Ray Burst
(GRB) studies. Its anti-solar pointing strategy makes the Earth cross the field
of view of its payload every orbit. In this paper, we present the variations of
the gamma-ray background of the two high energy instruments aboard SVOM, the
Gamma-Ray Monitor (GRM) and ECLAIRs, as a function of the Earth position. We
conclude with an estimate of the Earth influence on their sensitivity and their
GRB detection capability.Comment: 24 pages, 15 figures, accepted for publication in Experimental
Astronom
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