Optical follow up of the GRB 990123 source from UPSO, Nainital

TL;DR

This paper reports optical observations of the GRB 990123 afterglow, combining new CCD measurements with existing data to analyze its light curve and decay behavior, supporting fireball model predictions.

Contribution

It provides new CCD photometric measurements of the GRB 990123 optical transient and combines them with published data to analyze decay characteristics.

Findings

Decay constants in BV and R bands are approximately 1.1.

Optical flux decay is consistent with fireball models.

Optical transient observed about 12 hours post-burst.

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.