Claudia Wigger

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 GRB 021206 was almost fully linearly polarized. This was challenged by a subsequent reanalysis. We present a 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 instruments polarimetric sensitivity, and these simulations include photon polarization. For GRB 021206, we formally find a linear polarization degree of ΠGRB = 41%, concluding that the data quality is insufficient to constrain the polarization degree in this case. We further applied our analysis to GRB 030519B and again found a null result.

POLAR, a compact detector for Gamma Ray Bursts photon polarization measurements

The design and the simulated performances of a compact detector dedicated to the measurement of GRB photon polarization is presented. Such a detector would permit to answer the question “are most of the GRB strongly polarized?” in a mission of one year in space.

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

The Giant Flare of 2004 December 27 from SGR 1806–20

\chi^2

A new analysis of the short-duration, hard-spectrum GRB 051103, a possible extragalactic soft gamma repeater giant flare

, 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

OBSERVATIONS OF THE PROMPT GAMMA-RAY EMISSION OF GRB 070125

T_{90}

Observation of an Unexpected Hardening in the Spectrum of GRB 021206

as information and

Time resolved spectroscopy of GRB 030501 using INTEGRAL

\chi^2

The Interplanetary Network Supplement to the BeppoSAX Gamma-ray Burst Catalogs

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 /

Nonsolar astronomy with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

T_{90}