87 research outputs found
Limits on Neutrino Radiative Decay from Sn1987a
We calculate limits on the properties of neutrinos using data from gamma-ray
detectors on the Pioneer Venus Orbiter and Solar Max Mission satellites. A
massive neutrino decaying in flight from the supernova would produce gamma rays
detectable by these instruments. The lack of such a signal allows us to
constrain the mass, radiative lifetime, and branching ratio to photons of a
massive neutrino species produced in the supernova. Presented at Beyond The
Standard Model III, June, 1992.Comment: 5 Pages, 2 Figures (avalable on request). LaTeX, WorldSci.st
Strong spectral evolution during the prompt emission of GRB 070616
Swift has revealed features in GRB early light curves, such as steep decays
and X-ray flares, whose properties are consistent with an internal origin
though they are far from understood. The steep X-ray decay is often explained
using the curvature effect; however a significant number of GRBs display strong
spectral evolution during this phase, and a new mechanism must be invoked to
explain this. Of particular interest are the longest duration GRBs in which the
early emission can be studied in most detail. Here we present data for GRB
070616, in which the prompt emission shows a complex multipeaked structure,
leading to one of the longest prompt emission durations ever recorded. We take
advantage of extensive coverage of such a long burst by all Swift instruments.
Combining data from Swift and Suzaku we study the evolution of the prompt
emission spectrum, following the temporal variability of the peak energy and
spectral slope.Comment: 4 pages, 2 figures (Fig 1 in colour), contributed talk, submitted to
the proceedings of Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9
200
GRB-triggered searches for gravitational waves in LIGO data
The LIGO gravitational wave detectors have recently reached their design
sensitivity and finished a two-year science run. During this period one year of
data with unprecedented sensitivity has been collected. I will briefly describe
the status of the LIGO detectors and the overall quality of the most recent
science run. I also will present results of a search for inspiral waveforms in
gravitational wave data coincident with the short gamma ray burst detected on
1st February 2007, with its sky location error box overlapping a spiral arms of
M31. No gravitational wave signals were detected and a binary merger in M31 can
be excluded at the 99% confidence level.Comment: 5 pages, 3 figures, contributed talk, submitted to the proceedings of
Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9 200
The ECLAIRs telescope onboard the SVOM mission for gamma-ray burst studies
The X- and gamma-ray telescope ECLAIRs onboard the future mission for
gamma-ray burst studies SVOM (Space-based multi-band astronomical Variable
Objects Monitor) is foreseen to operate in orbit from 2013 on. ECLAIRs will
provide fast and accurate GRB triggers to other onboard telescopes, as well as
to the whole GRB community, in particular ground-based follow-up telescopes.
With its very low energy threshold ECLAIRs is particularly well suited for the
detection of highly redshifted GRB. The ECLAIRs X- and gamma-ray imaging camera
(CXG), used for GRB detection and localization, is combined with a soft X-ray
telescope (SXT) for afterglow observations and position refinement. The CXG is
a 2D-coded mask imager with a 1024 cm detection plane made of 8080
CdTe pixels, sensitive from 4 to 300 keV, with imaging capabilities up to about
120 keV and a localization accuracy better than 10 arcmin. The CXG permanently
observes a 2 sr-wide field of the sky and provides photon data to the onboard
science and triggering unit (UTS) which detects GRB by count-rate increases or
by the appearance of a new source in cyclic sky images. The SXT is a mirror
focusing X-ray telescope operating from 0.3 to 2 keV with a sensitivity of 1
mCrab for 100 s observations. The spacecraft slews within 3 min in
order to place the GRB candidate into the 2323 arcmin field of view
of the SXT, after which it refines the GRB position to about 10 arcsec. GRB
alerts are transmitted to ground-observers within tens of seconds via a VHF
network and all detected photons are available hours later for detailed
analysis. In this paper we present the ECLAIRs concepts, with emphasis on the
expected performances.Comment: on behalf of the ECLAIRs collaboration. Proceedings of Gamma-Ray
Bursts 2007 conference, Santa Fe, USA, 5-9 November 2007. Published in AIP
conf. proc. 1000, 581-584 (2008
Afterglows of Gamma-Ray Bursts: Short vs. Long GRBs
We compiled a large sample of Swift-era photometric data on long (Type II)
and short (Type I) GRB afterglows. We compare the luminosity and energetics of
the different samples to each other and to the afterglows of the pre-Swift era.
Here, we present the first results of these studies.Comment: Conference Proceedings, "Gamma-Ray Bursts 2007", Santa Fe, shortened
poster presentation; 4 pages, 3 figures; for full updated papers, go here to
arXiv:0712.2186 and also here to arXiv:0804.195
SVOM pointing strategy: how to optimize the redshift measurements?
The Sino-French SVOM mission (Space-based multi-band astronomical Variable
Objects Monitor) has been designed to detect all known types of gamma-ray
bursts (GRBs) and to provide fast and reliable GRB positions. In this study we
present the SVOM pointing strategy which should ensure the largest number of
localized bursts allowing a redshift measurement. The redshift measurement can
only be performed by large telescopes located on Earth. The best scientific
return will be achieved if we are able to combine constraints from both space
segment (platform and payload) and ground telescopes (visibility).Comment: Proceedings of Gamma-Ray Bursts 2007 conference, Santa Fe, USA, 5-9
November 2007. Published in AIP conf. proc. 1000, 585-588 (2008
Gamma-ray Bursts, Classified Physically
From Galactic binary sources, to extragalactic magnetized neutron stars, to
long-duration GRBs without associated supernovae, the types of sources we now
believe capable of producing bursts of gamma-rays continues to grow apace. With
this emergent diversity comes the recognition that the traditional (and newly
formulated) high-energy observables used for identifying sub-classes does not
provide an adequate one-to-one mapping to progenitors. The popular
classification of some > 100 sec duration GRBs as ``short bursts'' is not only
an unpalatable retronym and syntactically oxymoronic but highlights the
difficultly of using what was once a purely phenomenological classification to
encode our understanding of the physics that gives rise to the events. Here we
propose a physically based classification scheme designed to coexist with the
phenomenological system already in place and argue for its utility and
necessity.Comment: 6 pages, 3 figures. Slightly expanded version of solicited paper to
be published in the Proceedings of ''Gamma Ray Bursts 2007,'' Santa Fe, New
Mexico, November 5-9. Edited by E. E. Fenimore, M. Galassi, D. Palme
Direct and bulk-scattered forward-shock emissions: sources of X-ray afterglow diversity
I describe the modifications to the standard forward-shock model required to
account for the X-ray light-curve features discovered by Swift in the early
afterglow emission and propose that a delayed, pair-enriched, and highly
relativistic outflow, which bulk-scatters the forward-shock synchrotron
emission, yields sometimes a brighter X-ray emission, producing short-lived
X-ray flares, X-ray light-curve plateaus ending with chromatic breaks, and fast
post-plateau X-ray decays.Comment: 6 pages, submitted to the proceedings of 2007 GRB meeting, Santa Fe,
NM, Nov 5-9 200
Functional biases in GRB's spectral parameter correlations
Gamma Ray Bursts (GRBs) show evidence of different spectral shapes, light
curves, duration, host galaxies and they explode within a wide redshift range.
However, the most of them seems to follow very tight correlations among some
observed quantities relating to their energetic. If true, these correlations
have significant implications on burst physics, giving constraints on
theoretical models. Moreover, several suggestions have been made to use these
correlations in order to calibrate GRBs as standard candles and to constrain
the cosmological parameters. We investigate the cosmological relation between
low energy index in GRBs prompt spectra and the redshift . We
present a statistical analysis of the relation between the total isotropic
energy and the peak energy (also known as Amati relation) in
GRBs spectra searching for possible functional biases. Possible implications on
the vs relation of the vs correlation are
evaluated. We used MonteCarlo simulations and the boostrap method to evaluate
how large are the effects of functional biases on the vs . We
show that high values of the linear correlation coefficent, up to about 0.8, in
the vs relation are obtained for random generated samples of
GRBs, confirming the relevance of functional biases. Astrophysical consequences
from vs relation are then to be revised after a more accurate
and possibly bias free analysis.Comment: 6 pages, 6 figures, conference poster session: "070228: The Next
Decade of Gamma-Ray Burst Afterglows", Amsterdam, March 2007, MNRAS submitte
Gamma Ray Burst Central Engines
I review aspects of the theory of long-duration gamma-ray burst (GRB) central
engines. I focus on the requirements of any model; these include the angular
momentum of the progenitor, the power, Lorentz factor, asymmetry, and duration
of the flow, and both the association and the non-association with bright
supernovae. I compare and contrast the collapsar and millisecond proto-magnetar
models in light of these requirements. The ability of the latter model to
produce a flow with Lorentz factor ~100 while simultaneously maintaining a
kinetic luminosity of ~10^50 ergs/s for a timescale of ~10-100 s is emphasized.Comment: 6 pages; proceedings for "Gamma-Ray Bursts 2007," Santa Fe, New
Mexico, November 5-9; edited by M. Galassi, D. Palmer, and E. Fenimor
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