490 research outputs found
Gamma-Ray Bursts Observed with the Spectrometer SPI Onboard INTEGRAL
The spectrometer SPI is one of the main detectors of ESA's INTEGRAL mission.
The instrument offers two interesting and valuable capabilities for the
detection of the prompt emission of Gamma-ray bursts. Within a field of view of
16 degrees, SPI is able to localize Gamma-ray bursts with an accuracy of 10
arcmin. The large anticoincidence shield, ACS, consisting of 512 kg of BGO
crystals, detects Gamma-ray bursts quasi omnidirectionally above ~70 keV. Burst
alerts from SPI/ACS are distributed to the interested community via the
INTEGRAL Burst Alert System. The ACS data have been implemented into the 3rd
Interplanetary Network and have proven valuable for the localization of bursts
using the triangulation method. During the first 8 months of the mission
approximately one Gamma-ray burst per month was localized within the field of
fiew of SPI and 145 Gamma-ray burst candidates were detected by the ACS from
which 40 % have been confirmed by other instruments.Comment: 4 pages, 2 figures, to appear in the Proceedings of the Conference
"30 Years of GRB Discovery", Santa Fe, New Mexico, USA, September 8-12, 200
The first giant flare from SGR 1806-20: observations with the INTEGRAL SPI Anti-Coincidence Shield
A giant flare from the Soft Gamma-ray Repeater SGR 1806-20 has been detected
by several satellites on 2004 December 27. This tremendous outburst, the first
one observed from this source, was a hundred times more powerful than the two
previous giant flares from SGR 0525-66 and SGR 1900+14. We report the results
obtained for this event with the Anticoincidence Shield of the SPI spectrometer
on board the INTEGRAL satellite, which provides a high-statistics light curve
at E>~80 keV. The flare started with a very strong pulse, which saturated the
detector for ~0.7 s, and whose backscattered radiation from the Moon was
detected 2.8 s later. This was followed by a ~400 s long tail modulated at the
neutron star rotation period of 7.56 s. The tail fluence corresponds to an
energy in photons above 3 keV of 1.6x10^44 (d/15 kpc)^2 erg. This is of the
same order of the energy emitted in the pulsating tails of the two giant flares
seen from other soft repeaters, despite the hundredfold larger overall emitted
energy of the SGR 1806-20 giant flare. Long lasting (~1 hour) hard X-ray
emission, decaying in time as t^-0.85, and likely associated to the SGR 1806-20
giant flare afterglow has also been detected.Comment: revised version - Accepted for publication on The Astrophysical
Journal Letter
The sample of INTEGRAL SPI-ACS gamma-ray bursts
The anti-coincidence system of the spectrometer on board INTEGRAL is operated as a nearly omnidirectional gamma-ray burst detector above ∼ 75 keV. During the elapsed mission time 324 burst candidates were detected. As part of the 3rd Interplanetary Network of gamma-ray detectors the cosmic origin of 115 burst was confirmed. Here we present a preliminary analysis of the SPI-ACS gamma-ray burst sample. In particular we discuss the origin of a significant population of short events (duration < 0.2 s) and a possibleme thod for a flux calibration of thedata
Integral results on GRB030320: a long gamma-ray burst detected at the edge of the field of view
GRB030320 is the 5th Gamma-ray burst (GRB) detected by INTEGRAL in the field
of view (FoV). It is so far the GRB with the largest off-axis angle with
respect to the INTEGRAL pointing direction, near to the edge of the FoV of both
main instruments, IBIS and SPI. Nevertheless, it was possible to determine its
position and to extract spectra and fluxes. The GRB nature of the event was
confirmed by an IPN triangulation. It is a ~ 60 s long GRB with two prominent
peaks separated by ~ 35 s. The spectral shape of the GRB is best represented by
a single power law with a photon index Gamma ~ 1.7. The peak flux in the 20 -
200 keV band is determined to ~ 5.7 photons cm-2 s-1 and the GRB fluence to 1.1
x 10-5 erg cm-2. Analysing the spectral evolution of the GRB, a
``hard-to-soft'' behaviour emerges. A search for an optical counterpart has
been carried out, but none was found.Comment: 5 pages, 3 figures. Accepted for publication in A&AL (INTEGRAL issue
Measurements of Gamma-Ray Bursts (GRBs) with Glast
One of the scientific goals of the main instrument of GLAST is the study of
Gamma-Ray Bursts (GRBs) in the energy range from ~20 MeV to ~300 GeV. In order
to extend the energy measurement towards lower energies a secondary instrument,
the GLAST Burst Monitor (GBM), will measure GRBs from ~10 keV to ~25 MeV and
will therefore allow the investigation of the relation between the keV and the
MeV-GeV emission from GRBs over six energy decades. These unprecedented
measurements will permit the exploration of the unknown aspects of the
high-energy burst emission and the investigation of their connection with the
well-studied low-energy emission. They will also provide ne insights into the
physics of GRBs in general. In addition the excellent localization of GRBs by
the LAT will stimulate follow-up observations at other wavelengths which may
yield clues about the nature of the burst sources.Comment: 6 pages, 2 figures, to be published in Baltic Astronomy - Proceedings
of the minisymposium "Physics of Gamma-Ray Bursts", JENAM Conference, August
29-30, 2003, Budapes
INTEGRAL and Magnetars
Thanks to INTEGRAL's long exposures of the Galactic Plane, the two brightest
Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and
studied in detail for the first time at hard-X/soft-gamma rays. SGR 1806-20,
lying close to the Galactic Centre, and being very active in the past two
years, has provided a wealth of new INTEGRAL results, which we will summarise
here: more than 300 short bursts have been observed from this source and their
characteristics have been studied with unprecedented sensitivity in the 15-200
keV range. A hardness-intensity anticorrelation within the bursts has been
discovered and the overall Number-Intensity distribution of the bursts has been
determined. The increase of its bursting activity eventually led to the
December 2004 Giant Flare for which a possible soft gamma-ray (>80 keV) early
afterglow has been detected with INTEGRAL. The deep observations allowed us to
discover the persistent emission in hard X-rays (20-150 keV) from 1806-20 and
1900+14, the latter being in quiescent state, and to directly compare the
spectral characteristics of all Magnetars (two SGRs and three Anomalous X-ray
Pulsars) detected with INTEGRAL.Comment: 8 pages, 9 figures, Proceedings of the 6th INTEGRAL Workshop, Moscow,
2006 07 03-07, ESA SP-62
Detection of spectral evolution in the bursts emitted during the 2008-2009 active episode of SGR J1550 - 5418
In early October 2008, the Soft Gamma Repeater SGRJ1550 - 5418 (1E 1547.0 -
5408, AXJ155052 - 5418, PSR J1550 - 5418) became active, emitting a series of
bursts which triggered the Fermi Gamma-ray Burst Monitor (GBM) after which a
second especially intense activity period commenced in 2009 January and a
third, less active period was detected in 2009 March-April. Here we analyze the
GBM data all the bursts from the first and last active episodes. We performed
temporal and spectral analysis for all events and found that their temporal
characteristics are very similar to the ones of other SGR bursts, as well the
ones reported for the bursts of the main episode (average burst durations \sim
170 ms). In addition, we used our sample of bursts to quantify the systematic
uncertainties of the GBM location algorithm for soft gamma-ray transients to <
8 deg. Our spectral analysis indicates significant spectral evolution between
the first and last set of events. Although the 2008 October events are best fit
with a single blackbody function, for the 2009 bursts an Optically Thin Thermal
Bremsstrahlung (OTTB) is clearly preferred. We attribute this evolution to
changes in the magnetic field topology of the source, possibly due to effects
following the very energetic main bursting episode.Comment: 17 pages, 7 figures, 2 table
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