Interplanetary Network Localization of GRB 991208 and the Discovery of its Afterglow

Abstract

The extremely energetic (∼10-4 ergs cm-2) gamma-ray burst (GRB) of 1999 December 8 was triangulated to an ∼14 arcmin2 error box ∼1.8 days after its arrival at Earth with the third interplanetary network (IPN), which consists of the Ulysses, Near-Earth Asteroid Rendezvous, and Wind spacecraft. Radio observations with the Very Large Array ∼2.7 days after the burst revealed a bright fading counterpart whose position is consistent with that of an optical transient source with a redshift of 0.707. We present the time history, peak flux, fluence, and refined 1.3 arcmin2 error box of this event and discuss its energetics. This is the first time that a counterpart has been found for a GRB localized only by the IPN.