TITLE:   GCN CIRCULAR
NUMBER:  30842
SUBJECT: GRB 210812A is not a compelling example of a lensed GRB
DATE:    21/09/15 23:50:45 GMT
FROM:    Robert Nemiroff at Michigan Tech.  <nemiroff@mtu.edu>

Oindabi Mukherjee (Michigan Tech U.) & Robert J. Nemiroff (Michigan Tech
U.) report:

A preliminary light curve and hardness comparison between the two main
pulses of GRB 210812A has been done using Fermi GBM data to test for
gravitational lensing (as suggested by Veres et al. 2021, GCN 30645).

First, an amplitude-equalized light curve comparison of combined energy
bands 3  through 7 in detectors 2, 7, 8, 9, 10, 11, and 12 shows a chi^2
difference of 2.796 sigma, so that there is only a 0.52% chance of the two
pulses being randomly drawn from the same pulse.

Additionally, a hardness analysis shows that in energy channels 4 and 5,
the hardness difference between the two pulses differs at the 2.24 sigma
level, with the second pulse being softer.

These preliminary results suggest that although the case of GRB 210812A is
interesting, it  is not a compelling example of a GRB gravitational lens.

A more thorough analysis is ongoing.