Distortion of Gamma-Ray Burst Light Curves By Gravitational Microlensing

If at cosmological distances, a small fraction of gamma-ray bursts should be multiply imaged by intervening galaxies or clusters, resulting in the appearance of two very similar bursts from the same location with a relative time delay of hours to a year. We show that microlensing by individual stars in the lensing galaxy can smear out the light curves of the multiply imaged bursts on millisecond time scales. Therefore, in deciding whether two bursts are similar enough to qualify as multiple images, one must look at time scales longer than a few tens of milliseconds, since shorter time scales are possibly rendered dissimilar by microlensing. Key words: gamma-ray bursts -- gravitational lensing. 1 INTRODUCTION After more than two decades of observations, Gamma-Ray Bursts (GRBs) remain arguably the most puzzling phenomena in astronomy. In particular, their distance scale is yet to be established to everyone's satisfaction, with 100 kpc (Galactic corona) and z = 1 (¸ few Gpc) being the m..