[vsnet-grb-info 16666] GRB 150616A: Watcher optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17947
SUBJECT: GRB 150616A: Watcher optical upper limit
DATE:    15/06/18 16:07:20 GMT
FROM:    Antonio Martin-Carrillo at UCD,Space Science Group  <antonio.martin-carrillo at ucd.ie>

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

We observed the field of GRB 150616A (Lien et al., GCN Circ. #17936) using the 40cm Watcher telescope at Boyden Observatory in South Africa. 

Observations started at 22:52:09 UT, 170 seconds after the burst trigger. A series of 5 sec images were taken in the SDSS r' filter using an Andor CCD camera. 
No credible afterglow is found in any of the individual images at the enhanced XRT location (Evans et al., GCN Circ. #17937). A 3sigma upper limit for a combined 50 second exposure is given below.

Start             | End              | Exposure | Filter | Magnitude
-------------------------------------------------------------------------------------------------
22:52:09 UT | 22:53:15 UT | 10x5 sec |  r'       |  >18.9 (3sigma upper limit)

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

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