Prompt optical observations of Fermi-LAT bursts and GRB 090902B

摘要

Observations of high energy emission from gamma-ray bursts (GRBs) constrainthe extreme physical conditions associated with these energetic cosmicexplosions. The Large Area Telescope (LAT) onboard the Fermi Gamma-ray SpaceTelescope, a pair conversion telescope, observes energetic quanta from 30 MeVto > 300 GeV. Synergy of the LAT with the Gamma-ray Burst Monitor (GBM)enlarges the energy coverage to ~ 7.5 decades, very useful for studying the GRBemission itself. Prompt optical observations and their possible correlationswith photon emission at LAT energies help our understanding of the physicalmechanisms behind these events. The prompt response times and large fields ofof the ROTSE-III telescopes make afterglow observations possible for Fermibursts with ~ 1 degree localized errors. As an example, GRB 090902B, wasobserved starting ~ 4803 s after the burst. This is the earliest ground-basedoptical detection ever made for long-duration bursts sensed by the LAT. TheROTSE detection classifies the optical afterglow of GRB 090902B as one of thebrightest.