Fermi Gamma-ray Space Telescope

Improved GBM GRB localizations with BALROG

Francesco Berlato
(Jochen Greiner and Michael J. Burgess)


The Gamma-ray Burst Monitor (GBM) localizations are known to be affected by large systematic errors (Connaughton+2015). We present a systematic analysis of the BALROG algorithm which provides Fermi/GBM-detected GRB localizations free of systematic errors. This has become possible by fitting for position and spectrum simultaneously, rather than using a best-fitting Band function template (Burgess+2018). We compute BALROG localizations for 69 GRBs which have been also localized by Swift/BAT, and demonstrate the improvements relative to the localizations of Connaughton+2015.