Gamma‐Ray Burst Polarization: Limits fromRHESSIMeasurements

Using the RHESSI satellite as a Compton polarimeter, a recent study claimedthat the prompt emission of GRB021206 was almost fully linearly polarized. Thiswas challenged by a subsequent reanalysis. We present an novel approach,applying our method to the same data. We identify Compton scattering candidatesby carefully filtering events in energy, time, and scattering geometry. Ourpolarization search is based on time dependent scattering rates inperpendicular directions, thus optimally excluding systematic errors. Weperform simulations to obtain the instrument's polarimetric sensitivity, andthese simulations include photon polarization. For GRB021206, we formally finda linear polarization degree of 41% (+57% -44%), concluding that the dataquality is insufficient to constrain the polarization degree in this case. Wefurther applied our analysis to GRB030519B and found again a null result.Comment: 39 pages, 11 figures, accepted for publication by the Astrophysical Journa