TITLE:   GCN CIRCULAR
NUMBER:  14407
SUBJECT: GRB 130420A: ROTSE-III Detection of Optical Counterpart 
DATE:    13/04/20 08:08:48 GMT
FROM:    Tolga Guver at UA  <tolga@physics.arizona.edu>

GRB 130420A: ROTSE-III Detection of Optical Counterpart 

T. Guver (Sabanci U), report on behalf of the ROTSE collaboration: 
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 130420A (Swift trigger 553977). The first image was at 07:29:51.5 UT, 82.0 s after the burst (7.5 s after the GCN notice time). The unfiltered images are calibrated relative to USNO A2.0. We detect a 15.5 magnitude, fading source with coordinates: 

     13:04:25.5      +59:25:27.2    (J2000), with positional uncertainty of 1" or better

start UT mag mlim(of image) 
---------------------------------- 
07:34:12.7 15.5 16.5
This source is not visible in DSS (second epoch), 2MASS or the MPChecker database.

A jpeg image is available at http://www.rotse.net/images/gsq553977_3b03_img.jpg Note that the object marked 91 is the candidate in question.

Continuing observations are in progress.