80 research outputs found
Gamma-Ray Burst Detection with INTEGRAL/SPI
The spectrometer SPI, one of the two main instruments of the INTEGRAL
spacecraft, has strong capabilities in the Field of Gamma-Ray Burst (GRB)
detections. In its 16 degree Field of view (FoV) SPI is able to trigger and to
localize GRBs. With its large anticoincidence shield (ACS) of 512 kg of BGO
crystals SPI is able to detect GRBs quasi omnidirectionally with a very high
sensitivity. The ACS GRB alerts will provide GRB arrival times with high
accuracy but with no or very rough positional information. The expected GRB
detection rate in SPI's FoV will be one per month and for the ACS around 300
per year. At MPE two SPI software contributions to the real-time INTEGRAL
burst-alert system (IBAS) at the INTEGRAL science data centre ISDC have been
developed. The SPI-ACS branch of IBAS will produce burst alerts and
light-curves with 50 ms resolution. It is planned to use ACS burst alerts in
the 3rd interplanetary network. The SPI-FoV branch of IBAS is currently under
development at MPE. The system is using the energy and timing information of
single and multiple events detected by the Germanium-camera of SPI. Using the
imaging algorithm developed at the University of Birmingham the system is
expected to locate strong bursts with an accuracy of better than 1 degree.Comment: 11 pages, 5 figure
High-Energy Calibration of a BGO detector of the GLAST Burst Monitor
The understanding of the instrumental response of the GLAST Burst Monitor BGO
detectors at energies above the energy range which is accessible by common
laboratory radiation sources (< 4.43 MeV), is important, especially for the
later cross-calibration with the LAT response in the overlap region between ~
20 MeV to 30 MeV. In November 2006 the high-energy calibration of the GBM-BGO
spare detector was performed at the small Van-de-Graaff accelerator at SLAC.
High-energy gamma-rays from excited 8Be* (14.6 MeV and 17.5 MeV) and 16O* (6.1
MeV) were generated through (p,gamma)-reactions by irradiating a LiF-target.
For the calibration at lower energies radioactive sources were used. The
results, including spectra, the energy/channel-relation and the dependence of
energy resolution are presented.Comment: 2 pages, 1 figure; to appear in the Proc. of the First Int. GLAST
Symp. (Stanford, Feb. 5-8, 2007), eds. S.Ritz, P.F.Michelson, and C.Meegan,
AIP Conf. Pro
Six Years of Bursts with the SPI-ACS
The anticoincidence system of the INTEGRAL spectrometer has been an essential component of the
interplanetary network since launch. It has observed about 600 events which have been confirmed as
either soft gamma repeaters or cosmic gamma ray bursts by other instruments in the IPN. It has also
observed over 130 events which are unconfirmed, but which are almost certainly weak bursts below the
thresholds of the other IPN experiments. We review the highlights of these observations, which include
gamma-ray bursts, soft gamma repeaters, and one or two extragalactic giant magnetar flares
Evidence for 1809 keV Gamma-Ray Emission from 26Al Decays in the Vela Region with INTEGRAL/SPI
The Vela region is a promising target for the detection of 1.8 MeV gamma-rays
emitted by the decays of radioactive 26Al isotopes produced in hydrostatic or
explosive stellar nucleosynthesis processes. COMPTEL has claimed 1.8 MeV
gamma-ray detection from Vela at a 3sigma level with a flux of 3.6 10^-5
ph/cm^2/s. In this paper, we present first results of our search for 1.8 MeV
gamma-rays from Vela with the spectrometer SPI aboard INTEGRAL. Using the data
set acquired during 1.7 Ms at the end of 2005 in the frame of our AO-3
open-time observation, we determine a flux of (6.5 \pm 1.9(stat) \pm 2.4(syst))
10^-5 ph/cm^2/s from 26Al decays in the Vela region.Comment: 4 pages, 8 figures. Accepted for publication in ESA SP-622
(Proceedings of the 6th INTEGRAL Workshop, Moscow, 2006 07 03-07
The sharpness of gamma-ray burst prompt emission spectra
We aim to obtain a measure of the curvature of time-resolved spectra that can
be compared directly to theory. This tests the ability of models such as
synchrotron emission to explain the peaks or breaks of GBM prompt emission
spectra. We take the burst sample from the official Fermi GBM GRB time-resolved
spectral catalog. We re-fit all spectra with a measured peak or break energy in
the catalog best-fit models in various energy ranges, which cover the curvature
around the spectral peak or break, resulting in a total of 1,113 spectra being
analysed. We compute the sharpness angles under the peak or break of the
triangle constructed under the model fit curves and compare to the values
obtained from various representative emission models: blackbody,
single-electron synchrotron, synchrotron emission from a Maxwellian or
power-law electron distribution. We find that 35% of the time-resolved spectra
are inconsistent with the single-electron synchrotron function, and 91% are
inconsistent with the Maxwellian synchrotron function. The single temperature,
single emission time and location blackbody function is found to be sharper
than all the spectra. No general evolutionary trend of the sharpness angle is
observed, neither per burst nor for the whole population. It is found that the
limiting case, a single temperature Maxwellian synchrotron function, can only
contribute up to % of the peak flux. Our results show that even
the sharpest but non-realistic case, the single-electron synchrotron function,
cannot explain a large fraction of the observed GRB prompt spectra. Because of
the fact that any combination of physically possible synchrotron spectra added
together will always further broaden the spectrum, emission mechanisms other
than optically thin synchrotron radiation are likely required in a full
explanation of the spectral peaks or breaks of the GRB prompt emission phase.Comment: 16 pages, 13 figures, 2 tables, accepted for publication in A&
Six Years of Bursts with the SPI-ACS
The anticoincidence system of the INTEGRAL spectrometer has been an essential component of the
interplanetary network since launch. It has observed about 600 events which have been confirmed as
either soft gamma repeaters or cosmic gamma ray bursts by other instruments in the IPN. It has also
observed over 130 events which are unconfirmed, but which are almost certainly weak bursts below the
thresholds of the other IPN experiments. We review the highlights of these observations, which include
gamma-ray bursts, soft gamma repeaters, and one or two extragalactic giant magnetar flares
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
The spectral sharpness angle of gamma-ray bursts
We explain the results of Yu et al. (2015b) of the novel sharpness angle measurement to a large number of spectra obtained from the Fermi gamma-ray burst monitor. The sharpness angle is compared to the values obtained from various representative emission models: blackbody, single-electron synchrotron, synchrotron emission from a Maxwellian or power-law electron distribution. It is found that more than 91% of the high temporally and spectrally resolved spectra are inconsistent with any kind of optically thin synchrotron emission model alone. It is also found that the limiting case, a single temperature Maxwellian synchrotron function, can only contribute up to 58+23−18% of the peak flux. These results show that even the sharpest but non-realistic case, the single-electron synchrotron function, cannot explain a large fraction of the observed spectra. Since any combination of physically possible synchrotron spectra added together will always further broaden the spectrum, emission mechanisms other than optically thin synchrotron radiation are likely required in a full explanation of the spectral peaks or breaks of the GRB prompt emission phase
Broadband Spectral Investigations of SGR J1550-5418 Bursts
We present the results of our broadband spectral analysis of 42 SGR
J1550-5418 bursts simultaneously detected with the Swift/X-ray Telescope (XRT)
and the Fermi/Gamma-ray Burst Monitor (GBM), during the 2009 January active
episode of the source. The unique spectral and temporal capabilities of the XRT
Windowed Timing mode have allowed us to extend the GBM spectral coverage for
these events down to the X-ray domain (0.5-10 keV). Our earlier analysis of the
GBM data found that the SGR J1550-5418 burst spectra were described equally
well with a Comptonized model or with two blackbody functions; the two models
were statistically indistinguishable. Our new broadband (0.5 - 200 keV)
spectral fits show that, on average, the burst spectra are better described
with two blackbody functions than with the Comptonized model. Thus, our joint
XRT/GBM analysis clearly shows for the first time that the SGR J1550-5418 burst
spectra might naturally be expected to exhibit a more truly thermalized
character, such as a two-blackbody or even a multi-blackbody signal. Using the
Swift and RXTE timing ephemeris for SGR J1550-5418 we construct the
distribution of the XRT burst counts with spin phase and find that it is not
correlated with the persistent X-ray emission pulse phase from SGR J1550-5418.
These results indicate that the burst emitting sites on the neutron star need
not be co-located with hot spots emitting the bulk of the persistent X-ray
emission. Finally, we show that there is a significant pulse phase dependence
of the XRT burst counts, likely demonstrating that the surface magnetic field
of SGR J1550-5418 is not uniform over the emission zone, since it is
anticipated that regions with stronger surface magnetic field could trigger
bursts more efficiently.Comment: accepted for publication in The Astrophysical Journa
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