[vsnet-grb-info 13320] GRB 130515A: Gemini/GMOS Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14656
SUBJECT: GRB 130515A: Gemini/GMOS Observations
DATE:    13/05/15 06:32:58 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko at srl.caltech.edu>

S. B. Cenko (UC Berkeley), A Cucchiara (UCSC), D. Xu (DARK/NBI), and A. J.
Levan (U. Warwick) report on behalf of a larger collaboration:

We obtained a single 240 s r'-band image of the field of GRB 130515A
(Malesani et al., GCN 14650) with the Gemini Multi-Object Spectrograph
mounted on the 8 m Gemini South telescope.  The observation commenced at
01:59 UT (~ 38 min after the Swift trigger) under poor seeing conditions.

We identify the same 3 sources in the vicinity of the XRT error circle as
Dong et al. (GCN 14653).  For reference, we measure J2000.0 positions for
these sources with respect to nearby point sources from the 2MASS catalog
to be:

S1: 18:53:45.79, -54:16:47.1

S2: 18:53:45.23, -54: 16:44.4

S3: 18:53:46.13, -54:16:41.2

We have compared photometry from our Gemini images directly with that
obtained by the VLT approximately 50 minutes later. For these three point
sources, we measure the following change in magnitude (VLT - Gemini):

S1: -0.37 +/- 0.18 mag

S2: -0.03 +/- 0.10 mag

S3: -0.03 +/- 0.10 mag

There is this marginal evidence that S1 has brightened between the two
epochs.  However, we cannot rule out that the discrepancy results from a
color difference between the two images (r' vs R).

Further observations are planned.