[vsnet-grb-info 4809] GRB 070616: TLS observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6545
SUBJECT: GRB 070616: TLS observation
DATE:    07/06/17 01:39:22 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann at tls-tautenburg.de>

D. A. Kann, U. Laux, B. Stecklum and S. Klose (TLS Tautenburg) report:

We observed the field of Swift GRB 070616 (Starling et al., GCN 6542) with 
the Tautenburg 1.34m Schmidt telescope. A single 600 second image in Ic 
was obtained before clouds forced us to shut down. The airmass was 1.95.

At the XRT position (Starling et al., GCN 6542), we do not detect any 
afterglow. Assuming the USNO B1.0 star at RA = 02:08:34.67,
Dec. = +56:56:22.3 to have I = 15.44, we derive the following upper limit 
for the image:

date		time (days)	exp. time	Ic limit
070617.00838	0.32119		600		20.3

We caution that, as Starling et al. (GCN 6542) noted, this is very close 
to a star in the USNO B1.0 catalog. Thus, the true limiting magnitude at 
the XRT position is much shallower than what is stated above.

Judging from the early BAT/XRT light curve, this is a real GRB that 
happens to lie close to a bright star by chance. As the field is crowded, 
the probability of such a chance alignement is non-negligible.

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