TITLE:   GCN CIRCULAR
NUMBER:  6918
SUBJECT: GRB 071010B: TLS 2nd Epoch, refined analysis
DATE:    07/10/15 20:41:14 GMT
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".]