A Search for Millilensing Gamma-Ray Bursts in the Observations of Fermi GBM

Abstract

Millilensing of Gamma-Ray Bursts (GRBs) is expected to manifest as multiple emission episodes in a single triggered GRB with similar light-curve patterns and similar spectrum properties. Identifying such lensed GRBs could help improve constraints on the abundance of compact dark matter. Here we present a systemic search for millilensing among 3000 GRBs observed by the Fermi GBM up to 2021 April. Eventually we find 4 interesting candidates by performing auto-correlation test, hardness test, and time-integrated/resolved spectrum test to the whole sample. GRB 081126A and GRB 090717A are ranked as the first class candidate based on their excellent performance both in temporal and spectrum analysis. GRB 081122A and GRB 110517B are ranked as the second class candidates (suspected candidates), mainly because their two emission episodes show clear deviations in part of the time-resolved spectrum or in the time-integrated spectrum. Considering a point mass model for the gravitational lens, our results suggest that the density parameter of lens objects with mass M L ∼ 10 6 M is larger than 1.5 × 10 −3 .

GRB 201104A: A "repetitive" short gamma ray burst?

“…The cumulative hardness comparison in different energy bands is a simple but statistically powerful methodology (Mukherjee & Nemiroff 2021). And such a method has been used in some works (Wang et al 2021;Veres et al 2021;Lin et al 2021) as one of the indicators to confirm the lensed GRB.…”