VLBI observations of GRB afterglows

¹ National Radio Astronomy Observatory (NRAO), Socorro, NM 87801, U.S.A.
² Division of Physics, Mathematics, and Astronomy 105-24, California Institute of Technology, Pasadena, CA 91125, U.S.A.
³ Australia Telescope National Facility, CSIRO, Epping 2121, Australia

Send offprint request to: G.B. Taylor

Received: 29 December 1998
Accepted: 30 March 1999

Abstract

Once the afterglow from a GRB has been detected in the radio, Very Long Baseline Interferometry (VLBI) observations can provide a resolution of 1 milliarcsecond or better and absolute astrometry at a similar level. We will review the VLBI programs carried out to date which include observations of G970508, G980329, G980425, and G980703. All of these objects are found to be very compact (size  mas) even months after the burst. This is consistent with the predictions of fireball models. Our ultimate goal is a direct measurement of the morphology and expansion of a GRB afterglow.