[vsnet-grb-info 16804] GRB 150727A: Watcher optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18085
SUBJECT: GRB 150727A: Watcher optical upper limit
DATE:    15/07/28 10:39:46 GMT
FROM:    Antonio Martin-Carrillo at UCD,Space Science Group  <antonio.martin-carrillo at ucd.ie>

A. Martin-Carrillo (UCD), D. Murphy (UCD), L. Hanlon (UCD), M. Topinka (CTU), H. J. van Heerden (UFS), B. van Soelen (UFS) and P. J. Meintjes (UFS):

We observed the field of GRB 150727A (Cenko et al., GCN Circ. #18076) using the 40cm UCD Watcher telescope at Boyden Observatory in South Africa. 

Observations started at 19:19:55 UT, 1073 seconds after the burst trigger. A series of 60 sec images were taken in the SDSS r' filter using an Andor CCD camera. 
No afterglow candidate is detected in any of the individual images at the UVOT location. A 3sigma upper limit for a combined 180 second exposure is given below.

Start             | End              | Exposure | Filter | Magnitude
-------------------------------------------------------------------------------------------------
19:19:55 UT | 19:25:20 UT | 3x60 sec |  r'       |  >17.59 (3sigma upper limit)

The upper limit was calculated using nearby stars from the APASS catalogue.

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