Light-curve Test of GRB 090717 as a Gravitationally Lensed Echo

Abstract

Abstract Light curve comparison is a simple but statistically powerful test for the presence of gravitational lensing in gamma-ray bursts (GRBs). Since gravitational lensing does not change relative timing internal to images, all source images created by gravitational lensing should show the same light curve to within a scale factor in amplitude. Applied to the recent claim that the two pulses in GRB 090717 are lensed images of the same pulse, it was found that the light curves for these pulses actually differ at about the 5.0σ confidence level (99.999956%) in a χ 2 comparison test. Under the given assumptions, GRB 090717 therefore does not present a compelling example of gravitational lensing.