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 ± 0.23, 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 fv ∝ v1/3. Within the standard synchrotron fireball model, this requires that the external medium be less dense than 104 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 > 25.7 and K > 23.3. The lack of a host galaxy likely implies that it is either substantially subluminous or more distant than a redshift of ∼1.2.
Publication Source (Journal or Book title)
Schaefer, B., Snyder, J., Hernandez, J., Roscherr, B., Deng, M., Ellman, N., Bailyn, C., Rengstorf, A., Smith, D., Levine, A., Barthelmy, S., Butterworth, P., Hurley, K., Cline, T., Meegan, C., Kouveliotou, C., Kippen, R., Park, H., Williams, G., Porrata, R., Bionta, R., Hartmann, D., Band, D., Frail, D., Kulkarni, S., Bloom, J., Djorgovski, S., Sadava, D., Chaffee, F., Harris, F., Abad, C., Adams, B., & Andrews, P. (1999). Discovery of the optical transient of GRB 990308. Astrophysical Journal, 524 (2 PART 2) https://doi.org/10.1086/312318