GCN Circular 6918
Subject
GRB 071010B: TLS 2nd Epoch, refined analysis
Event
Date
2007-10-15T20:41:14Z (18 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann, C. Hoegner & R. Filgas (TLS Tautenburg) report:
We observed the afterglow (Oksanen, GCN 6873) of GRB 071010B (Markwardt et
al., GCN 6871) with the Tautenburg 1.34m Schmidt telescope under good
conditions, obtaining 16 600 second images in the Rc band at 3.2 to 3.3
days after the GRB. The afterglow is clearly detected in all frames. Using
two USNO B1.0 stars (RA (J2000) = 10:02:09.93, Dec. (J2000) = +45:41:18.4,
R2=16.80; RA (J2000) = 10:02:23.11, Dec. (J2000) = +45:41:41.1, R2=16.94),
we revise our original photometry (Kann, Hoegner & Filgas, GCN 6884) using
fully reduced images:
Date Mid-Time Rc dRc
11.06361 0.19848 19.145 0.041
11.07113 0.20600 19.121 0.033
11.07865 0.21352 19.198 0.030
11.08617 0.22104 19.163 0.062
11.13149 0.26637 19.396 0.032
11.13902 0.27389 19.512 0.223 (Clouds)
Using the same comparison stars, we derive the following magnitudes from
our new images:
Date Mid-Time Rc dRc
14.05372 3.18859 20.800 0.139
14.06126 3.19613 20.815 0.142
14.06878 3.20365 20.779 0.092
14.07630 3.21117 20.852 0.088
14.08382 3.21869 20.921 0.095
14.09133 3.22621 20.899 0.097
14.09885 3.23372 20.888 0.088
14.10638 3.24125 20.839 0.079
14.11389 3.24877 20.967 0.090
14.12141 3.25628 20.946 0.078
14.12892 3.26380 21.014 0.093
14.13644 3.27131 20.929 0.075
14.14395 3.27882 20.814 0.071
14.15146 3.28634 20.732 0.066
14.15899 3.29386 20.792 0.069
14.16650 3.30138 20.864 0.076
We note that the last data points seem to indicate a small rebrightening
feature which was receding again when twilight stopped our observations.
With Rc ~ 20.9 at 3.2 days after the GRB, the afterglow is among the
brightest observed so far (Kann, Klose & Zeh 2006, ApJ, 641, 993; Kann et
al., in preparation). Using data from Arto Oksanen
(http://murtoinen.dyndns.org/ccd/grb/grb071010/) and Im, Lee & Urata (GCN
6897), we find that the afterglow can be fit with a broken power law with
pre-break slope alpha_1 = 0.3 +/- 0.083, post-break slope alpha_2 = 0.575
+/- 0.009, and break time t_b = 0.049 +/- 0.019 days. The very shallow
decay (Kann, Hoegner & Filgas, GCN 6884, Templeton et al., GCN 6903) is
thus seen to continue, which is highly unusual.
Further observations are planned and encouraged at other facitlities.
This message may be cited.
[GCN OPS NOTE(16oct07): Per author's request, the typo in the first line
was changed from "071013" to "071010B".]