The 2009 Fermi Symposium

Fermi GBM Observations of Three Intense Short GRBs

Sylvain Guiriec, UA Huntsville

Abstract:

In its first 14 months of operation, GBM has detected more than 300 GRBs, of which ∼20% are short (t90 < 2 s). Here we present results for three short GRBs (GRB 090227B, GRB090228 and GRB 090510) that are intense enough to allow detailed time-resolved spectroscopy. GBM, with its combination of NaI and BGO detectors, is able to follow Epeak over a very wide energy range and to track spectral evolution on timescales down to several milliseconds. For two of the GRBs, the Band GRB function is statistically preferred over the cutoff power law function which has formerly sufficed for most short GRBs. Short GRBs are known to be hard, but there have been different reports on how the values of the parameters of Band GRB fits differ from long GRBs. We find that these short GRBs have exceptionally high Epeak values. The spectral evolution patterns are broadly similar to long GRBs, but there are hints of some differences.