GCN Circular 13639
Subject
GRB 120805A: optical afterglow confirmation from the NOT
Event
Date
2012-08-14T12:10:51Z (13 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
D. Malesani, T. Kruehler (DARK/NBI), A. de Ugarte Postigo (IAA/CSIC and
DARK/NBI), D. Xu (WIS), N. R. Tanvir (Univ. Leicester), J. Gorosabel
(IAA/CSIC), P. Jakobsson (Univ. Iceland), S. Geier (NOT and DARK/NBI),
T. Pursimo (NOT), report on behalf of a larger collaboration.
We observed the field of GRB 120805A (Troja et al., GCN 13588) on two
epochs with the NOT optical telescope, located in La Palma (Canary
Islands). The two observations were carried out on mean dates Aug 5.936
and 13.896 UT, that is 1.0 hr and 8.0 days after the GRB, respectively.
The source first noticed by Gorosabel et al. (GCN 13591) is detected in
both our images, and it varied significantly between the two epochs, as
well as compared to the CAHA report (Gorosabel et al., GCN 13591). We
note that the object position is now fully consistent with the revised
XRT error circle (Evans, GCN 13638). We thus conclude that this source
is the optical afterglow of GRB 120805A.
The source varied by only about 2 mag between the two NOT epochs
(corresponding to a power-law decay slope of ~0.3), suggesting that in
the later image the host galaxy could be contributing to the total light.
A picture showing the two NOT epochs is posted at this URL:
http://www.astro.ku.dk/~malesani/GRB/120805A/GRB120805A_comparison.jpg
We thank Phil Evans for discussion about the XRT localization of this
afterglow.