GCN Circular 3110
Subject
GRB 050315, SMARTS optical afterglow decay
Date
2005-03-17T21:04:47Z (20 years ago)
From
Bethany Cobb at Yale U <cobb@astro.yale.edu>
B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained additional optical/IR imaging of the reported optical afterglow
candidate (GCN 3100, Kelson & Berger) of GRB 050315
(GCN 3094, Parsons et al.) beginning ~35.6 hours post-burst.
Total summed exposure times amounted to 10 minutes R and I and
12.5 minutes in J.
The source identified as the afterglow candidate has dimmed
since our previous observations (GCN 3104, Cobb & Bailyn).
Preliminary comparison with Landolt Standards PG 1047+003 and RU 149
yields the following approximate afterglow magnitudes:
R = 21.6
I = 21.5
The counterpart was again not detected in the IR, with a
magnitude limit of J > 18.6.
Our R and I observations are summarized below:
time post-burst: R magnitude: I magnitude:
11.6 hours 20.9 20.3
35.6 hours 21.6 21.5
We note that the I-band observations are close to the detection
limit, and have measurement errors of >0.2 magnitudes, so the
evidence for a color change should be treated with caution.
The R-band magnitudes have errors of ~0.2, so assuming
a power-law afterglow decay (afterglow flux proportional to
t^alpha), then this corresponds to an alpha of -0.57 +\- 0.25.