TITLE:   GCN CIRCULAR
NUMBER:  30645
SUBJECT: GRB 210812A is consistent with being a lensed GRB
DATE:    21/08/13 20:34:35 GMT
FROM:    Peter Veres at UAH  <veresp@gmail.com>

P. Veres (UAH) reports on behalf of the Fermi-GBM team:

"
Fermi GBM triggered on GRB 210812A at 16:47:01 UT on 12 Aug 2021 (trigger
650479626 / 210812699). Location information can be found in the Fermi GBM
team GCN 30633.

The lightcurve of GRB 210812A consists of two pulses, separated by about 33
s. The two pulses have similar shapes, the first pulse being approximately
5 times brighter.

The best fitting spectral shapes are consistent between the pulses. The
hardness ratio as a function of time also shows a consistent evolution.

These observations suggest that the two pulses are gravitationally lensed
manifestations of a single pulse.

Assuming a point mass lens model (e.g. Mao 1992, ApJL, 839, 41), the mass
of the lens is about 10^6 Msun.

GRB 210812A was also detected by INTEGRAL/SPI-ACS.

This analysis is preliminary, further analysis is ongoing. We encourage
follow-up observations.
"