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THE ASTRONOMER Electronic Circular No 3181      2016 Jun 30 20.03UT
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 160625B: BRIGHT GLOW PRE TRIGGER

A. Melandri (INAF-OAB), and others report (GCN 19585) on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the Fermi/LAT-detected
burst GRB 160625B in a series of observations tiled on the sky. The total
exposure time is 2.7 ks, distributed over 8 tiles; the maximum exposure at a
single sky location was 1.1 ks. The data were collected between T0+9.6 ks
and T0+10.0 ks, and are entirely in Photon Counting (PC) mode. 

An uncatalogued X-ray source is detected and is above the RASS limit, and is
therefore likely the GRB afterglow.  The position of this source is RA,
Dec=308.5969, +6.9196 which is equivalent to:

RA (J2000): 20:34:23.25
Dec(J2000): +06:55:10.5

with an uncertainty of 3.8 arcsec (radius, 90% confidence).  This position
is 19.7 arcmin from the Fermi/LAT position. 


Subsequently on GCN 19615 T. Batsch et. al., (Pi of the Sky
Collaboration)relay:

One of four Pi of the Sky North detectors located at Arenosillo observatory
in Mazagón near Huelva, Spain imaged the region of GRB 160625B, at a
position:
RA  20h 34m 23.50s DEC +6 55’ 8.1” before, during and after the GRB with 10s
exposures (the exposures were taken in white light, IR-cut and UV-cut
filters only, to achieve deepest detection limit).

Cameras of the Pi of the Sky North observatory were observing the position
of the GRB160625B 48s after Fermi GBM trigger 488587220 time (Jun 25
22:40:16.28 UT) 140 seconds before the LAT 488587408 trigger (Jun 25
22:43:24.82 UT). We observed optical emission at the position given by Swift
XRT recording a bright light curve starting -5.9 s before the LAT trigger. 

The first 10 s exposure shows initial magnitude of ~9.18 (unfiltered)
brightening to ~8.04 on the second exposure, than becoming gradually dimmer.

It is important to note that both cameras, 35 and 39, identified a new
object on exposures starting just before the time of the trigger. 

Editor: If anyone has by chance images of this area around:
Jun 25 22:40:16.28 UT
Please check for an optical outburst and if detected please send to the
editor with caption details.

Guy M Hurst