Optical follow up of the GRB 990123 sources from UPSO, Naini Tal

Abstract

The CCD magnitudes in Johnson $BV$ and Cousins R photometric passbands are determined for the optical transient of GRB 990123. These observations have been taken approximately 12 hours after trigger of the gamma-ray burst. BVR photometric light curves are obtained by combining the published data with the present measurements. They indicate that the flux decay constants in BV and R passbands are almost the same. Its value is $1.1\pm 0.06$. Such decay is quite consistent with the fireball models for the optical transient.