Fermi Gamma-ray Space Telescope

GRB and Solar Flare Polarimetry with CGRO/COMPTEL

Mark McConnell
(Audrey Coleman (UNH), Werner Collmar (MPE), and Andreas Zoglauer (UCB))


The COMPTEL instrument on the Compton Gamma Ray Observatory operated on orbit from 1991-2000. As a Compton telescope, it was intrinsically sensitive to polarization, although the geometry of the design was not optimal for polarization studies. We have embarked on a program to analyze CGRO/COMPTEL data in search for evidence of polarization in both GRBs and solar flares. We are pursuing this work because of the heightened interest in high energy polarimetry, the recognition that some high energy sources may be highly polarized (thus improving our chances of a making useful measurements), and the ready availability of modern computing resources that provide the ability to carry out more comprehensive simulations in support of the analysis. The only significant work done to date with regards to COMPTEL polarimetry was published almost 20 years ago and used a simplified mass model of COMPTEL for simulating the instrument response. Estimates of the minimum detectable polarization (MDP) near 1 MeV suggests MDP values as low as 10% for a bright GRB or solar flare. We have systematically reviewed all GRB and solar flare data collected by COMPTEL in search of candidate events suitable for a more focused analysis. We will present the latest results of this work.