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Radio Monitoring of the January 11 , 1997 Gamma-Ray Burst

We report on a comprehensive radio monitoring program of the bright gamma-ray burster GRB 970111. These VLA observations were made at a frequency of 1.4 GHz (λ = 20 cm) and span a range of post-burst timescales between 28 hours and one month. Despite extensive sampling at sub-milliJansky sensitivities, no radio source was detected above 0.5 mJy in the current best error box (∼14 arcmin2) for GRB 970111. A highly unusual radio source, VLA J1528.7+1945, was seen to drop in flux density by a factor of two in our monitoring period but it lies outside the error box and thus it is unlikely to be related to GRB 970111. Cosmological fireball models of gamma-ray bursts make predictions of late-time emission occurring at longer wavelengths. The absence of a flaring or fading radio counterpart to GRB 970111 provides strong constraints on these models. Subject headings: gamma rays: bursts radio continuum: general National Radio Astronomy Observatory, Socorro, NM, 87801, USA Division of Physics, Mathematics and Astronomy 105-24, Caltech, Pasadena CA 91125, USA Istituto di Astrofisica Spaziale, CNR, Via E. Fermi, 21, 00044 Frascati, Italy Dipartimento di Fisica, Universita’ di Ferrara, Via Paradiso 12, I-44100 Ferrara, Italy Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Via P. Gobetti 101, I-40129 Bologna, Italy Space Research Organization, Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands