GCN Circular 12343
Subject
GRB 110915A: NOT observations
Date
2011-09-16T00:26:36Z (13 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
D. Malesani (DARK, NBI), P. Jakobsson (U. Iceland), A. de Ugarte Postigo
(DARK, NBI), J. Lykke (NOT), D. Xu (WIS), and N. R. Tanvir (U.
Leicester) report on behalf of a larger collaboration:
Using ALFOSC on the Nordic Optical Telescope (NOT) we have obtained
R-band (3 x 600 s) and z-band (18 x 300 s) imaging of the GRB 110915A
field (Holland et al., GCN 12335) starting on 2011 September 15.87 UT
(around 7.5 hr after the burst).
We do not detect any object within the refined XRT error circle (Evans
et al., GCN 12340). The limiting magnitudes are R(Vega) = 24.3 and z(AB)
= 23.5, calibrated against the USNO-B1 and SDSS catalogs, respectively.
Using our R-band limit and preliminary X-ray fluxes, we obtain a
corresponding upper limit on beta_OX of around 0.1, rendering the burst
dark according to the definition proposed by Jakobsson et al. (2004,
ApJ, 617, L21). This burst may therefore be at high redshift, or suffer
from significant dust extinction. The presence of significant excess
absorption in the X-ray afterglow spectrum
(http://www.swift.ac.uk/xrt_spectra/00503219/) makes the second option
more likely.