arXiv subjects
Publications and source records attributed to C. Wigger.
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.
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.
The Gamma-ray instruments on-board INTEGRAL offer an unique opportunity to perform time resolved analysis on GRBs. The imager IBIS allows accurate positiioning of GRBs and broad band spectral analysis, while SPI provides high resolution spectroscopy. GRB 030501 was discovered by the INTEGRAL Burst Alert System in the ISGRI field of view. Although the burst was fairly weak (fluence F = 3.5 * 10^-6 erg cm^-2 in the 20-200 keV energy band) it was possible to perform time resolved spectroscopy with a resolution of a few seconds. The GRB shows a spectrum in the 20 - 400 keV range which is consistent with a spectral photon index of -1.7. No emission line or spectral break was detectable in the spectrum. Although the flux seems to be correlated with the hardness of the GRB spectrum, there is no clear soft to hard evolution seen over the duration of the burst. The INTEGRAL data have been compared with results from the Ulysses and RHESSI experiments.
The time anomaly of neutrino events observed in the KARMEN detector at the ISIS facility is discussed. We show that beam-correlated neutron events are not completely suppressed by the KARMEN lower energy cut and could cause the observed deviation of the measured time distribution from an exponential curve with tau = 2.2 microseconds.
We have searched for the pion decay pi^+ --> mu^+ X, where X is a neutral particle of mass 33.905 MeV. This process was suggested by the KARMEN Collaboration to explain an anomaly in their observed time distribution of neutrino induced reactions. Having measured the muon momentum spectrum of charged pions decaying in flight, we find no evidence for this process and place an upper limit on the branching fraction eta leq 6.0 * 10^{-10} of such a decay at a 95% confidence level.