628 research outputs found
Gamma-Ray Burst Polarization: Limits from RHESSI Measurements
Using the RHESSI satellite as a Compton polarimeter, a recent study claimed
that the prompt emission of GRB021206 was almost fully linearly polarized. This
was challenged by a subsequent reanalysis. We present an novel approach,
applying our method to the same data. We identify Compton scattering candidates
by carefully filtering events in energy, time, and scattering geometry. Our
polarization search is based on time dependent scattering rates in
perpendicular directions, thus optimally excluding systematic errors. We
perform simulations to obtain the instrument's polarimetric sensitivity, and
these simulations include photon polarization. For GRB021206, we formally find
a linear polarization degree of 41% (+57% -44%), concluding that the data
quality is insufficient to constrain the polarization degree in this case. We
further applied our analysis to GRB030519B and found again a null result.Comment: 39 pages, 11 figures, accepted for publication by the Astrophysical
Journa
RHESSI as Gamma Ray Burst Polarimeter
The Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) was designed to measure hard X-rays and γ-rays from solar flares. With its big detection area and thin side shielding it also proved to be well suited for studying
Gamma Ray Bursts (GRB). Polarization analysis is feasible as well, due to a big modulation factor (MF), though serious constraints on the minimum detectable polarization
(MDP) come from detection efficiency of double scattered photons. More constraints are given by background of accidental and real coincidences
Search for Gamma-Ray Burst Classes with the RHESSI Satellite
A sample of 427 gamma-ray bursts (GRBs), measured by the RHESSI satellite, is
studied statistically with respect to duration and hardness ratio. Standard
statistical tests are used, such as , F-test and the maximum likelihood
ratio test, in order to compare the number of GRB groups in the RHESSI database
with that of the BATSE database. Previous studies based on the BATSE Catalog
claim the existence of an intermediate GRB group, besides the long and short
groups. Using only the GRB duration as information and or
F-test, we have not found any statistically significant intermediate group in
the RHESSI data. However, maximum likelihood ratio test reveals a significant
intermediate group. Also using the 2-dimensional hardness / plane, the
maximum likelihood analysis reveals a significant intermediate group. Contrary
to the BATSE database, the intermediate group in the RHESSI data-set is harder
than the long one. The existence of an intermediate group follows not only from
the BATSE data-set, but also from the RHESSI one.Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 4
figure
Spectral Analysis of GRBs Measured by RHESSI
The Ge spectrometer of the RHESSI satellite is sensitive to Gamma Ray Bursts
(GRBs) from about 40 keV up to 17 MeV, thus ideally complementing the Swift/BAT
instrument whose sensitivity decreases above 150 keV. We present preliminary
results of spectral fits of RHESSI GRB data. After describing our method, the
RHESSI results are discussed and compared with Swift and Konus.Comment: 4 pages, 4 figures, conference proceedings, 'Swift and GRBs:
Unveiling the Relativistic Universe', San Servolo, Venice, 5-9 June 2006, to
appear in Il Nouvo Ciment
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