[vsnet-grb-info 5242] GRB 071010B: Light Curve Break Confirmed

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6935
SUBJECT: GRB 071010B: Light Curve Break Confirmed
DATE:    07/10/18 22:28:48 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann at tls-tautenburg.de>

D. A. Kann, U. Laux, R. Filgas (TLS Tautenburg), A. Oksanen (Hankasalmi 
Observatory, Hankasalmi, Finland), S. Covino (Brera), V. D'Elia (Rome), V. 
Lorenzi (INAF/TNG), and R. Decarli (Como) report:

At 7 days after the GRB, we obtained further Rc band imaging of the GRB 
071010B (Markwardt et al., GCN 6871) afterglow (Oksanen, GCN 6873). We 
obtained a single 600 second image with the Tautenburg 1.34m Schmidt 
telescope under bad conditions (passing clouds, high humidity, wind). The 
afterglow is only faintly detected. Furthermore, we obtained 5 x 180 sec 
images with the TNG telescope in La Palma. The afterglow is clearly 
detected in each image and there is no evidence for underlying extended 
emission. Finally, at dawn, we obtained 4 x 100 sec Rc images with the 
NOT.

Using the same comparison stars as Kann, Hoegner & Filgas (GCN 6918), we 
derive the following magnitude:

Date		Mid-Time	Rc	dRc	Exposure	Telescope

18.10966	7.24453		21.593	0.244	1 x 600		TLS
18.20581	7.34069		21.801	0.028	5 x 180		TNG
18.26479	7.39966		21.756	0.106	4 x 100		NOT

These values confirm the light curve break first reported by Kann, Laux & 
Filgas (GCN 6923). Using all data available so far (see GCN 6918 and GCN 
6923 for references), we find preliminary fit results for data after 0.05 days:

alpha_1 = 0.56 +/- 0.01, alpha_2 = 1.46 +/- 0.10, t_b = 3.44 +/- 0.39 
days.

The post-break slope is still quite shallow, leaving open if this was a 
jet break or not. We note that the first break at 0.049 days (GCN 6918) 
has Delta alpha ~ 0.26 and therefore may be a cooling break.

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