Hardness Test of GRB 950830 as a Gravitationally Lensed Echo

TL;DR

This study uses a spectral hardness comparison to test for gravitational lensing in GRB 950830, finding some evidence but not conclusive proof of lensing effects.

Contribution

It introduces a model-independent spectral hardness test to evaluate gravitational lensing in gamma-ray bursts, applied specifically to GRB 950830.

Findings

Second pulse appears weaker in one energy channel

Difference is statistically significant above 90%

Results suggest lensing is intriguing but not proven

Abstract

Cumulative hardness comparisons are a simple but statistically powerful test for the presence of gravitational lensing in gamma-ray bursts (GRBs). Since gravitational lensing does not change photon energies, all source images should have the same spectra -- and hence hardness. Applied to the recent claim that the two pulses in GRB 950830 are lensed images of the same pulse, the measured flux ratio between the two main pulses should be the same at all energies. After summing up all the counts in both of GRB 950830's two pulses in all four BATSE energy bands, it was found that in energy channel 3, the second pulse appears somewhat weak. In comparison with the other BATSE energy channels, the difference was statistically significant at above 90\%. This model-independent test indicates that the case for GRB 950830 involving a gravitational lens may be intriguing -- but should not be considered proven.