47 research outputs found
Gamma-Ray Bursts, witnessing the birth of stellar mass black holes
Gamma-ray bursts are associated with catastrophic cosmic events. They appear
when a new black hole, created after the explosion of a massive star or the
merger of two compact stars, quickly accretes the matter around it and ejects a
transient relativistic jet in our direction. This review discusses the various
types of gamma-ray bursts, their progenitors, their beaming and their rate in
the local universe. We emphasize the broad astrophysical interest of GRB
studies, and the crucial role of high-energy satellites as exclusive suppliers
of GRB alerts and initial locations.Comment: 8 pages, 2 figures, invited review at the conference "An INTEGRAL
view of the high-energy sky (the first 10 years) - 9th INTEGRAL Workshop and
celebration of the 10th anniversary of the launch" - to appear in Proceedings
of Science - PoS(INTEGRAL 2012)11
Investigating the impact of optical selection effects on observed rest frame prompt GRB properties
Measuring gamma-ray burst (GRB) properties in their rest-frame is crucial to
understand the physics at work in gamma-ray bursts. This can only be done for
GRBs with known redshift. Since redshifts are usually measured from the optical
spectrum of the afterglow, correlations between prompt and afterglow emissions
may introduce biases in the distribution of rest-frame properties of the prompt
emission. Our analysis is based on a sample of 90 GRBs with good optical
follow-up and well measured prompt emission. 76 of them have a measure of
redshift and 14 have no redshift. We estimate their optical brightness with
their R magnitude measured two hours after the trigger and compare the rest
frame prompt properties of different classes of GRB afterglow brightness. We
find that the optical brightness of GRBs in our sample is mainly driven by
their intrinsic afterglow luminosity. We show that GRBs with low and high
afterglow optical fluxes have similar Epi , Eiso , Liso , indicating that the
rest-frame distributions computed from GRBs with a redshift are not
significantly distorted by optical selection effects. However we found that the
rest frame T90 distribution is not immune to optical selection effect, which
favor the selection of GRBs with longer durations. Finally, we note that GRBs
in the upper part of the Epi-Eiso plane have fainter optical afterglows and we
show that optical selection effects strongly favor the detection of GRBs with
bright afterglows located close or below the best-fit Epi-Eiso relation, whose
redshift is easily measurable.Comment: 41 pages, 10 figures, 7 tables. arXiv admin note: substantial text
overlap with arXiv:1503.0276
An improved redshift indicator for Gamma-Ray Bursts, based on the prompt emission
We propose an improved version of the redshift indicator developed by Atteia
(2003), which gets rid of the dependence on the burst duration and provides
better estimates for high-redshift GRBs. We present the derivation and the
definition of this redshift indicator, then its calibration with 17 GRBs with
known redshifts detected by HETE-2 and 2 more detected by Konus-Wind. We also
provide an estimation of the redshift for 59 bursts, and we finally discuss the
redshift distribution of HETE-bursts and the possible other applications of
this redshift indicator.Comment: To appear in the proceedings of the 16th Annual October Astrophysics
Conference in Maryland, "Gamma Ray Bursts in the Swift Era", Washington DC.,
November 29-December 2, 2005, 4 pages, 3 figure
Optically Selected GRB Afterglows, a Real Time Analysis System at the CFHT
We attempt to detect optical GRB afterglows on images taken by the Canada
France Hawaii Telescope for the Very Wide survey, component of the Legacy
Survey. To do so, a Real Time Analysis System called "Optically Selected GRB
Afterglows" has been installed on a dedicated computer in Hawaii. This pipeline
automatically and quickly analyzes Megacam images and extracts from them a list
of variable objects which is displayed on a web page for validation by a member
of the collaboration. The Very Wide survey covers 1200 square degrees down to
i'=23.5. This paper briefly explain the RTAS process.Comment: 4 pages, 3 figures, accepted for publication in Il Nuovo Ciment
A Comprehensive Study of Short Bursts from SGR 1806-20 and SGR 1900+14 Detected by HETE-2
We present the results of temporal and spectral studies of the short burst
(less than a few hundred milliseconds) from the soft gamma repeaters (SGRs)
1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005,
HETE-2 detected 50 bursts which were localized to SGR 1806-20 and 5 bursts
which were localized to SGR 1900+14. Especially SGR 1806-20 was active in 2004,
and HETE-2 localized 33 bursts in that year. The cumulative number-intensity
distribution of SGR 1806-20 in 2004 is well described by a power law model with
an index of -1.1+/-0.6. It is consistent with previous studies but burst data
taken in other years clearly give a steeper distribution. This may suggest that
more energetic bursts could occur more frequently in periods of greater
activity. A power law cumulative number-intensity distribution is also known
for earthquakes and solar flares. It may imply analogous triggering mechanisms.
Although spectral evolution during bursts with a time scale of > 20 ms is not
common in the HETE-2 sample, spectral softening due to the very rapid (< a few
milliseconds) energy reinjection and cooling may not be excluded. The spectra
of all short bursts are well reproduced by a two blackbody function (2BB) with
temperatures ~4 and ~11 keV. From the timing analysis of the SGR 1806-20 data,
a time lag of 2.2+/-0.4 ms is found between the 30-100 keV and 2-10 keV
radiation bands. This may imply (1) a very rapid spectral softening and energy
reinjection, (2) diffused (elongated) emission plasma along the magnetic field
lines in pseudo equilibrium with multi-temperatures, or (3) a separate (located
at < 700 km) emission region of softer component (say, ~4 keV) which could be
reprocessed X-rays by higher energy (> 11 keV) photons from an emission region
near the stellar surface.Comment: 50 pages, 14 figures, accepted for publication in PAS