[vsnet-grb-info 4425] GRB 070311: Tautenburg sees afterglow fading

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6206
SUBJECT: GRB 070311: Tautenburg sees afterglow fading
DATE:    07/03/14 22:09:44 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann at tls-tautenburg.de>

D. A. Kann, R. Filgas & C. Hoegner (TLS Tautenburg) report:

We observed the position of the optical/NIR afterglow (Covino et al., GCN 
6190, Bloom, GCN 6191, Halpern & Armstrong, GCN 6195) of GRB 070311 
(Mereghetti et al., GCN 6189) with the 1.34m Schmidt Telescope of the 
Thueringer Landessternwarte Tautenburg. Observing conditions were good but 
the image depth was affected by light pollution.

We obtained 6 x 600 sec images with the Rc filter. Observation midtime was 
March 14.80113 UT, which is 3.72277 days after the GRB.

At the position of the GRB afterglow, we detect a very faint source at the 
limit of the image (which is Rc > 23.4, 2 sigma). Using the same USNO 
comparison star that Halpern & Armstrong (GCN 6195) use, we derive the 
following magnitude:

dt (days)	Rc mag	dmag

3.72277		23.35	0.37

We caution that the detection is marginal and may not represent a real 
source. On the other hand, it is clear that the afterglow has faded, 
probably around one magnitude, between the rebrightening seen by Halpern & 
Armstrong (GCN 6203) and Greco et al. (GCN 6204). Thus, we conclude that 
it is probably not a low redshift GRB exhibiting the early rise of SN 
emission.

Still, the rebrightening is interesting and further deep photometric 
follow-up is warranted. No further observations are planned at TLS as we 
will not be able to reach deeper limiting magnitudes for this object.

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