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

TL;DR

This paper reports on prompt optical observations of Fermi-LAT gamma-ray bursts, highlighting the earliest ground-based optical detection of GRB 090902B, and discusses the physical insights gained from multi-wavelength data.

Contribution

It presents the first early optical detection of a Fermi-LAT burst, demonstrating the synergy between gamma-ray and optical observations for understanding GRB physics.

Findings

GRB 090902B's optical afterglow was the brightest observed.

Optical detection occurred ~4803 seconds after the burst.

The observation provides new constraints on GRB emission mechanisms.

Abstract

Observations of high energy emission from gamma-ray bursts (GRBs) constrain the extreme physical conditions associated with these energetic cosmic explosions. The Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope, a pair conversion telescope, observes energetic quanta from 30 MeV to > 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 GRB emission itself. Prompt optical observations and their possible correlations with photon emission at LAT energies help our understanding of the physical mechanisms behind these events. The prompt response times and large fields of of the ROTSE-III telescopes make afterglow observations possible for Fermi bursts with ~ 1 degree localized errors. As an example, GRB 090902B, was observed starting ~ 4803 s after the burst. This is the earliest ground-based optical detection ever made for long-duration bursts sensed by the LAT. The ROTSE detection classifies the optical afterglow of GRB 090902B as one of the brightest.