The Astrophysical Journal
The American Astronomical Society
The optical transient of the faint gamma-ray burst GRB 990308 was detected by the QUEST camera on the Venezuelan 1 m Schmidt telescope starting 3.28 hr after the burst. Our photometry gives V= 18.32 ± 0.07, R = 18.14 ± 0. 06, B =18.65, and R=18.22 ± 0.05 for times ranging from 3.28 to 3.47 hr after the burst. The colors correspond to a spectral slope of close to f ∝ v^1/3 . Within the standard synchrotron ﬁreball model, this rquires that the external medium be less dense than 10^4 cm^-3, the electrons contain more than 20% of the shock energy, and the magnetic ﬁeld energy be less than 24% of the energy in the electrons for normal interstellar or circumstellar densities. We also report upper limits of V > 12.0 at 132 s (with LOTIS), V > 13.4 from 132 to 1029 s (with LOTIS), V > 15.3 at 28.2 minutes (with Super-LOTIS), and a 8.5 GHz ﬂux of less than 114 μJy at 110 days (with the Very Large Array). Wisconsin-Indiana-Yale-NOAO 3.5 m and Keck 10 m telescopes reveal this location to be empty of any host galaxy to R > 25.7and K > 123.3. The lack of a host galaxy likely implies that it is either substantially subluminous or more distant than a redshift of ∼1.2.
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