Gravitational Lensing of Relativistic Fireball

The gravitational lensing of a relativistic fireball can produce the time delayed multiple images with quite different spectra and temporal patterns in contrast with a nonrelativistic source and hence can imitate the source recurrence. In particular, the enigmatic four multiple gamma-ray bursts detected during two days at October 1996 in the same sky region may be due to a single fireball event multiply imaged by the foreground galactic nucleus or cluster of galaxies.