TITLE:   GCN CIRCULAR
NUMBER:  20844
SUBJECT: GRB170306A: SALT observations
DATE:    17/03/10 20:05:16 GMT
FROM:    Soebur Razzaque at U of Johannesburg  <srazzaque@uj.ac.za>

D.A.H. Buckley (SAAO/SALT), A, Martin-Carrillo (U. College Dublin), S. Razzaque (U. Johannesburg) and R. Skelton (SAAO/SALT) report on behalf of a larger collaboration.

We observed the nominal position of GRB 170306A (Markwardt et al. GCN 20819 and Guidorzi et al. GCN 20820) on 2017-03-07 at 01:22:42 UTC using the Southern African Large Telescope (SALT) in Sutherland, South Africa, 18.61 h after the Swift GRB trigger. A 20 sec r'-band image was obtained using SALTICAM just prior to the commencement of attempted low resolution (R ~ 355 at 660 nm) spectroscopy. Two stellar objects at r’ ~ 19 and 20 were seen, with FWHM of 1.7 arcsec, near the GRB position and long slit spectroscopy was attempted of both. Only the brighter one provided a detection, which was noisy and showed no obvious spectral features. Subsequent information provided by P. Schady on possible optical candidates from the first GROND observation (Schady et al. GCN 20822) was used to confirm the identification of the r’ = 20.4 object identified by Schady (GCN 20843) as the optical counterpart. The SALT image shows a very weak detection of this object, barely above the background, with an estimated brightness of r’= 21.4 +/- 0.3, having dimmed approximately one magnitude since detection.

We thank Patricia Schady and Christiano Guidorzi for providing information to assist in the identification of the optical counterpart.

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