Evidence for Gravitational Lensing of GRB 200716C

Observationally, there is a small fraction of gamma-ray bursts (GRBs) with prompt emission observed by Fermi/GBM that are composed of two pulses. Occasionally, the distance to a GRB may be lensed when a high mass astrophysical object resides in the path between the GRB source and observer. In this paper, we describe GRB 200716C, which has a two-pulse emission and duration of a few seconds. We present a Bayesian analysis identifying gravitational lensing in both temporal and spectral properties, and calculate the time delay (Δt ~ 1.92 s) and magnification (γ ~ 1.5) between those two pulses based on the temporal fits. One can roughly estimate the lens mass to be about 2.4 × 10⁵M_⊙ in the rest frame. We also calculate the false alarm probability for this detection to be about 0.07% with trial factors, and a present-day number density of about 808Mpc^-3 with an energy density Ω ~ 1.4 × 10^-3. If the first pulse of this GRB near the trigger time is indeed gravitationally echoed by a second pulse, GRB 200716C may be a short GRB candidate with extended emission.