GCN Circular 16656

D. Xu (DARK/NBI), S. Schulze (PUC, MAS), M. El-Souri, S. Boye Nissen,
M. Sparre, J. P. U. Fynbo (DARK/NBI), A. de Ugarte Postigo (IAA-CSIC,
DARK/NBI), P. Jakobsson (U. Iceland) report on behalf a larger
collaboration:

We observed the field of GRB 140801A (Fermi trigger 428612396) with
the 2.5-m Nordic Optical Telescope (NOT) equipped with ALFOSC. We
obtained a 200-s exposure in each of V, R, and I bands. Observations
started at 01:07:23 UT on August 2 (i.e. 6.12 hours after the burst).

The optical transient reported by Gorbovskoy et al. (GCN 16653
Not found
 
 
) is
clearly detected in each of our images at the same position. And it
has decayed to R(Vega) ~ 20.6 mag at 6.15 hours post-trigger,
calibrated against two bright nearby USNO B1 stars. This measurement
is not corrected for foreground extinction.

The OT roughly decays as t^-1.5 during the MASTER observations (GCN
16653
Not found
 
 
), and then changes to roughly as t^-0.9 assuming a simple
power-law decline since the MASTER's end-time. The whole behavior is
similar to that of previous GRB optical afterglows. We thus conclude
that this OT is very likely the optical afterglow of GRB 140801A.