257 research outputs found
The first GRB survey of the IBIS/PICsIT archive
The multi-purpose INTEGRAL mission is continuously contributing to Gamma Ray
Burst (GRB) science, thanks to the performances of its two main instruments,
IBIS and SPI, operating in the hard X-ray/soft gamma-ray domain. We investigate
the possibilities offered to the study of GRBs by PICsIT, the high-energy
detector of the IBIS instrument. We searched for transient episodes in the
PICsIT light curves archive from May 2006 to August 2009, using stringent
criteria optimized for the detection of long events. In the time interval under
examination PICsIT provides an energy coverage from 208 to 2600 keV, resolved
in eight energy channels, combined with a fine time resolution of 16 ms. PICsIT
successfully observes GRBs in the 260-2600 keV energy range with an incoming
direction spread over half the sky for the brightest events. We compiled a list
of 39 bursts, most of which are confirmed GRBs or simultaneous to triggers from
other satellites/instruments. We produced light curves with a time sampling
down to 0.25 s in three energy intervals for all events. Because an adequate
response matrix is not yet available for the PICsIT burst sample, we obtained a
calibration coefficient in three selected energy bands by comparing
instrumental counts with physical fluences inferred from observations with
different satellites. The good time resolution provided by the PICsIT data
allows a spectral variability study of our sample through the hardness ratio.Comment: 20 pages, 48 figures. Accepted for publication in A&
Extended Emission from Short Gamma-Ray Bursts Detected with SPI-ACS/INTEGRAL
The short duration (T90 < 2 s) gamma-ray bursts (GRBs) detected in the
SPI-ACS experiment onboard the INTEGRAL observatory are investigated. Averaged
light curves have been constructed for various groups of events, including
short GRBs and unidentified short events. Extended emission has been found in
the averaged light curves of both short GRBs and unidentified short events. It
is shown that the fraction of the short GRBs in the total number of SPI-ACS
GRBs can range from 30 to 45%, which is considerably larger than has been
thought previously.Comment: 27 pages, 10 figure
Annihilation radiation in cosmic gamma-ray bursts
The pair annihilation radiation in gamma-ray bursts is seen as broad lines with extended hard wings. This radiation is suggested to escape in a collimated beam from magnetic polar regions of neutron stars
A general scheme for modeling gamma-ray burst prompt emission
We describe a general method for modeling gamma-ray burst prompt emission. We
find that for the burst to be produced via the synchrotron process unphysical
conditions are required -- the distance of the source from the center of the
explosion () must be larger than cm and the source
Lorentz factor \gta 10^3; for such a high Lorentz factor the deceleration
radius () is less than even if the number density of particles
in the surrounding medium is as small as cm. The result,
, is in contradiction with the early x-ray and optical
afterglow data. The synchrotron-self-Compton (SSC) process fares much better.
There is a large solution space for a typical GRB prompt emission to be
produced via the SSC process. The prompt optical emission accompanying the
burst is found to be very bright (\lta 14 mag; for ) in the SSC
model, which exceeds the observed flux (or upper limit) for most GRBs.
Continuous acceleration of electrons can significantly reduce the optical flux
and bring it down to the observed limits. (Abridged)Comment: Published in MNRAS Jan 2008, 56 page
Observations of giant outbursts from Cygnus X-1
We present interplanetary network localization, spectral, and time history
information for 7 episodes of exceptionally intense gamma-ray emission from
Cygnus X-1. The outbursts occurred between 1995 and 2003, with durations up to
\~28000 seconds. The observed 15 - 300 keV peak fluxes and fluences reached
3E-7 erg /cm2 s, and 8E-4 erg / cm2 respectively. By combining the
triangulations of these outbursts we derive an ~1700 square arcminute (3 sigma)
error ellipse which contains Cygnus X-1 and no other known high energy sources.
The outbursts reported here occurred both when Cyg X-1 was in the hard state as
well as in the soft one, and at various orbital phases. The spectral data
indicate that these outbursts display the same parameters as those of the
underlying hard and soft states, suggesting that they represent another
manifestation of these states.Comment: 27 pages, 9 figures. Revised version. Accepted for publication in the
Astrophysical Journal, tentatively scheduled for October 20, 2003 Part
Konus-Wind and Helicon-Coronas-F Observations of Solar Flares
Results of solar flare observations obtained in the Konus-Wind experiment
from November, 1994 to December, 2013 and in the Helicon Coronas-F experiment
during its operation from 2001 to 2005, are presented. For the periods
indicated Konus-Wind detected in the trigger mode 834 solar flares, and
Helicon-Coronas-F detected more than 300 solar flares.
A description of the instruments and data processing techniques are given. As
an example, the analysis of the spectral evolution of the flares
SOL2012-11-08T02:19 (M 1.7) and SOL2002-03-10T01:34 (C5.1) is made with the
Konus-Wind data and the flare SOL2003-10-26T06:11 (X1.2) is analyzed in the
2.223 MeV deuterium line with the Helicon-Coronas-F data.Comment: Published version. A list of the Konus-Wind solar flare triggers and
figures of their time profiles are available at
http://www.ioffe.ru/LEA/Solar
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