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THE ASTRONOMER Electronic Circular No 2910      2013 Apr 26 09.52UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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GRB 130427A
Further to TA E-Circular E2909, the predicted exceptionally slow decline 
mentioned by several professionals did allow extensive monitoring of 
this gamma ray burster well beyond the trigger stage. It also appears 
the RAPTOR images indicate it had been as bright as magnitude R=7.4 
BEFORE the trigger as detailed below.

Peter Birtwhistle responded in the early evening with positive recording 
and measurement:

2013 04 27.86219 11 32 32.83 +27 41 56.0          16.71R      J95

This was a stack with total exposure of 200 seconds, reduced using 
CMC-14 catalogue, with the 0.40-m Schmidt-Cassegrain + CCD.

This was followed by a GCN notice:

A. Volnova, Moscow et. al., report (GCB 14474) on behalf of larger GRB 
follow-up collaboration:

We started observation of the field of the Swift GRB 130427A with AZT-11 
telescope of CrAO observatory on Apr. 27 (UT) 18:21:45 in VRI filters. 
We clearly detect that the optical counterpart was still bright. 
Preliminary photometry follows:

    filter   tstart (UT) exp,s   T-t0,d       OT +/- err
    R       18:21:45   120      0,76580   16,71 +/- 0,06
    R       18:27:52   120      0,77005   16,87 +/- 0,06
    R       18:34:00   120      0,77431   16,83 +/- 0,07
    R       18:40:07   120      0,77855   16,81 +/- 0,06

On GCN circular 14476 James Wren et. al., at Los Alamos National 
Laboratory relayed:

Three RAPTOR full-sky persistent monitors at Maui, HI, and Los Alamos, 
NM, independently detected bright optical emission at the location of 
GRB 130427A. Starting at 07:47:07.28 UT (50.2 seconds before the Swift 
trigger) we detect a brightening counterpart which peaks at magnitude 
R~7.4.  After the peak, the source fades to below 10th magnitude at 
approximately the Swift trigger time.  The unfiltered images from all 
three monitors are calibrated to the Tycho-2 V-band catalog.

Martin Mobberley has now reported:
I have measured last night's GRB image, despite Astrometrica only 
finding 4 stars to work with in the barren field......

It comes up with RA 11h 32m 32.81s DEC +27 41' 56.1" and an unfiltered 
magnitude of 16.9 on 2013 April 27th at 21:20 UT.

Editor:
Given the bright phase around the trigger time (approx. 07h50m) on April 
27, could we please ask all imagers to check their records to see if any 
pictures were taken of the area on April 26/27. Even negative results 
for this period should be included in any reports sent to the editor.

Guy M Hurst