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GCN Circular 16668

GRB 140808A: optical afterglow candidate iPTF14eag
2014-08-08T09:40:43Z (10 years ago)
Leo Singer at CIT/PTF <>
L. P. Singer (Caltech), M. M. Kasliwal (Carnegie Observatories/Princeton),
V. B. Bhalerao (IUCAA), S. B. Cenko (NASA/GSFC), D. A. Perley (Caltech), 
and J. Johansson (Stockholm University) report on behalf of the
intermediate Palomar Transient Factory (iPTF) collaboration:

Fermi GBM triggered on GRB 140808A (Fermi trigger 429152043 /
140808038) at 2014-08-08 00:54:00.62. At 04:08:50 (3.25 hours after
the burst), we began our search for optical counterparts using the
Palomar 48-inch Oschin telescope (P48). We began searching 13 fields
spanning 95 deg2, covering most of the 1-sigma statiscal+systematic
region of the final Fermi GBM localization. We estimate a 69% chance
that these fields contain the true location of the source.

Sifting through candidate variable sources using image subtraction
and standard iPTF vetting procedures, we detected several optical

iPTF14eag, at the coordinates:
 RA(J2000)  =  14h 44m 53.33s (221.222219 deg)
 Dec(J2000) = +49d 12' 51.1"  (+49.214207 deg)

This source was detected at R = 18.91 +/- 0.06 mag at 3.35 hours
after the burst, and faded to R = 19.29 +/- 0.10 by 4.91 hours.
Relative to the time of the burst, this decay fits a power law
with index alpha = -0.9 +/- 0.3.

There were no previous iPTF detections at this position through 2014
May 28, and there are no coincident sources in SDSS.

iPTF14eai, at the coordinates:
 RA(J2000)  =  14h 17m 29.91s (214.374606 deg)
 Dec(J2000) = +47d 07' 30.1"  (+47.125041 deg)

This candidate was detected at R = 19.37 +/- 0.11 mag at 3.27 hours
after the burst, and was possibly fading. It is coincident with the
r = 18.43 galaxy SDSS J141729.93+470729.7. Because the galaxy is not
resolved in our P48 images, we caution that the transient's magnitude
derived from image subtraction is tentative.

iPTF14eac, at the coordinates:
 RA(J2000)  =  14h 25m 07.98s (216.283253 deg)
 Dec(J2000) = +50d 32' 04.1"  (+50.534476 deg)

This source was detected at R = 18.30 +/- 0.06 at 3.44 hours after
the burst. There was an earlier possible R = 20.16 +/- 0.21 mag
detection from coadded P48 images on 2014 June 09. It is located in a
spiral arm of PGC2375699.

Given the rapid fading of iPTF14eag and the lack of a host or
quiescent counterpart, we propose it as an optical afterglow
candidate. We have requested Swift TOO observations. We encourage
spectroscopic and photometric follow-up to confirm the nature of the

The diagram shows the
locations of our candidates and the 13 P48 fields in relation to the
Fermi GBM 1- and 2-sigma statistical+systematic contours.
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