GCN Circular 824
Subject
GRB 000926, Optical Observations
Date
2000-09-30T22:04:07Z (24 years ago)
From
Jules Halpern at Columbia U. <jules@astro.columbia.edu>
J. P. Halpern, N. Mirabal (Columbia U.), D. Turnshek
& J. Busche (U. Pittsburgh) report on behalf of the
MDM Observatory GRB follow-up team:
"We processed and calibrated the MDM R and B data reported
previously in GCN #806, now using Landolt standard stars,
and we acquired new R and B observations on the MDM 2.4.
The comparison star at (J2000) RA 17:04:01.21, Dec +51:46:19.9,
previously assumed to have R = 17.1, is now measured at
R = 17.06, B = 18.50. In this new system, we find the
following magnitudes for the OT:
Sep. 28.183 B = 20.89 +/- 0.04
Sep. 28.177 R = 19.86 +/- 0.02
Sep. 29.176 B = 22.11 +/- 0.09
Sep. 29.196 R = 21.14 +/- 0.03
Sep. 30.179 B = 23.07 +/- 0.06
Sep. 30.211 R = 22.11 +/- 0.06
Correcting the observed B-R for the Galactic extinction
A_B = 0.101, A_R = 0.063 of Schlegel et al., we find that
B-R = 0.95 +/- 0.05 consistently for these three nights.
This color corresponds to spectral slope beta = -1.51 +/- 0.12,
which indicates that there may be intrinsic extinction.
Our latest R-band measurement confirms the steepening of the
decay reported by Fynbo et al. (GCN #820) and Veillet (GCN #823).
For the first 2 days the decay slope was consistent with
alpha = -1.65 +/- 0.02. After 2.2 days, alpha = -2.51 +/- 0.17.
Images of this field and an updated decay curve are posted at
http://www.astro.columbia.edu/~jules/grb/000926
This message may be cited."