GCN Circular 12010

D. A. Kann, S. Schmidl, B. Stecklum and C. Hoegner (TLS Tautenburg) report:

Observations of GRB 110503A (M. Stamatikos et al., GCN 11991
Not found
 
 
) and its
afterglow are continuing at TLS Tautenburg (D. A. Kann et al., GCN 11996
Not found
 
 
).
In the first night, we observed for a total of 6 hours, with conditions
becoming worse (increasing airmass and passing clouds). 43 detections in
BVRIZ were secured.

In the second night, observational conditions were challenging, with
passing clouds and high airmass at the time observations could begin. We
obtained 3 x 300 s in Rc, 3 x 450 s in V and only a single 450 s B
observation. The afterglow is faintly detected in the Rc and V stacks as
well as the B image. Using the comparison star of GCN 11996
Not found
 
 
, as calibrated
by A. Updike et al. (GCN 12001
Not found
 
 
), we find:

t (days after trigger) = 1.24878, Rc = 21.39 +/- 0.12

We re-observed the afterglow position in the third night under moderate
conditions (low airmass, good seeing, but low transparency). We obtained 6
x 600 s in the Rc band. Even in the stack, the afterglow is only faintly
detected. We find:

t (days after trigger) = 2.14026, Rc = 22.63 +/- 0.28

Fitting our Rc band data shows a clear break, with alpha_1 = 0.83 +/-
0.03, alpha_2 = 2.3 +/- 0.6 (due to sparse data with large errors), t_b =
1.06 +/- 0.14 days. While both the post-break decay slope as well as the
break time are insecure due to sparsity of the data, the data point at
2.14 days lies a complete magnitude under the extrapolation of the early
decay, making the existence of a break itself secure.

We propose this is the jet break of the afterglow.

Deeper follow-up with telescopes of larger aperature is highly encouraged.

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