Evaluation of Automated Fermi GBM Localizations of Gamma-Ray Bursts

Goldstein, A. and Fletcher, C. and Veres, Péter and Briggs, M.S. and Cleveland, W.H. (2020) Evaluation of Automated Fermi GBM Localizations of Gamma-Ray Bursts. ASTROPHYSICAL JOURNAL, 895 (1). ISSN 1538-4357

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Abstract

The capability of the Fermi Gamma-ray Burst Monitor (GBM) to localize gamma-ray bursts (GRBs) is evaluated for two different automate algorithms: the GBM Team's RoboBA algorithm and the independentl developed BALROG algorithm. Through a systematic study utilizing ove 500 GRBs with known locations from instruments like Swift and the Ferm LAT, we directly compare the effectiveness of, and accurately estimat the systematic uncertainty for, both algorithms. We show simpl adjustments to the GBM Team's RoboBA, in operation since early 2016 yields significant improvement in the systematic uncertainty, removin the long tail identified in the systematic, and improves the overal accuracy. The systematic uncertainty for the updated RoboB localizations is $1.8^\\circ$ for 52% of GRBs and $4.1^\\circ$ for th remaining 48%. Both from public reporting by BALROG and our systemati study, we find the systematic uncertainty of $1-2^\\circ$ quoted in GC circulars for bright GRBs localized by BALROG is an underestimate of th true magnitude of the systematic, which we find to be $2.7^\\circ$ fo 74% of GRBs and $33^\\circ$ for the remaining 26%. We show that, once th systematic uncertainty is considered, the RoboBA 90% localizatio confidence regions can be more than an order of magnitude smaller i area than those produced by BALROG.

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