GCN Circular 476
Subject
GRB 991216, optical observations
Date
1999-12-17T22:18:03Z (25 years ago)
From
Saurabh Jha at CfA <saurabh@mondatta.harvard.edu>
S. Jha, R. Kirshner, K. Stanek, P. Garnavich, M. Garcia,
A. Szentgyorgyi (CfA), and J. Tonry (U. Hawaii) report:
We imaged the optical transient reported by Uglesich et al. (GCN 472)
with the U. Hawaii 2.2-m telescope on Dec 17.61 UT. The source is
clearly detected in each of two 300s R-band exposures. Though
conditions were photometric, the observations were made at high
airmass (~3), making precise absolute photometry difficult.
Differential photometry with respect to 30 USNO-A2.0 stars in the
images yields a magnitude estimate for the transient of R = 19.4 +/-
0.1 (internal error). This is the same magnitude derived by Uglesich
et al. for their Dec. 17.312 UT observation, but it is possible that
our two zeropoints are not identical.
With respect to the reference star used by Henden et al. (GCN 473),
we find an R magnitude difference of 4.29 magnitudes. This together
with the data of Henden et al. gives an R-band power-law decay
index of 1.0 +/- 0.2.
Given the lack of a precise calibration for comparison stars in the
field, we also list the R magnitude difference between the transient
and two stars very near the transient from our Dec 17.61 UT images:
Star Position (J2000) Transient - Star
A (USNO-A2.0 975.01388002) 05:09:29.799 +11:17:08.47 +4.12 mag
B (anonymous) 05:09:32.132 +11:17:23.75 -0.04 mag
A finder chart with the proposed comparison stars labelled is available
at http://cfa-www.harvard.edu/cfa/oir/Research/GRB/grb991216.jpg.
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