Interplanetary Network Localization of GRB991208 and the Discovery of its Afterglow

The extremely energetic (~10^-4 erg/cm^2) gamma-ray burst (GRB) of 1999 December 8 was triangulated to a ~14 sq. arcmin. error box ~1.8 d after its arrival at Earth with the 3rd interplanetary network (IPN), consisting of the Ulysses, Near Earth Asteroid Rendezvous (NEAR), and WIND spacecraft. Radio observations with the Very Large Array ~2.7 d after the burst revealed a bright fading counterpart whose position is consistent with that of an optical transient source whose redshift is z=0.707. We present the time history, peak flux, fluence, and refined 1.3 sq. arcmin. 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.