Distortion of gamma-ray burst light curves by gravitational microlensing

If they are located 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.