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GCN Circular 16226

GRB 140508A: iPTF optical transient candidate
2014-05-08T19:30:09Z (10 years ago)
Leo Singer at CIT/PTF <>
L. P. Singer (Caltech), S. B. Cenko (NASA/GSFC), M. M. Kasliwal
(Carnegie Observatories/Princeton), Christoffer Fremling (Stockholm
University), and Yifat Dzigan (Weizmann) report on behalf of the
intermediate Palomar Transient Factory (iPTF) collaboration:

We have searched for an optical counterpart of GRB 140508A (Yu and
Goldstein, GCN 16224), Fermi/GBM trigger 421211037 (2014-05-08
03:03:54.60), using the Palomar 48-inch Oschin telescope (P48). Based
on the final Fermi GBM localization, we observed 10 fields covering
73 deg2, with an estimated 67% chance of containing the true location
of the event. Due to weather at Palomar early in the night,
observations started at 09:48 UTC, 6.7 hours after the trigger.

Also detected by Konus-Wind, INTEGRAL, Swift BAT (outside FoV), and
MESSENGER, the IPN error box (Hurley et al., GCN 16225) was mostly
contained within two CCDs in one of our fields.

Sifting through candidate variable sources using image subtraction
and standard iPTF vetting procedures, we detected several optical
transients. Only is located within the IPN error box:

iPTF14aue, at the coordinates:
  RA(J2000)  =  17h 01m 51.95s (255.466450 deg)
  Dec(J2000) = +46d 46' 49.5"  (+46.780417 deg)

The source was detected at r = 17.89 +/- 0.01 mag and appeared to
fade. A power-law fit to the first two observations, relative to the
time of the GBM trigger, gives a decay index of alpha = 1.12 +/- 0.1.
There is no source coincident with this location in our reference
images or in SDSS DR10.

This position is also consistent with the IPN triangulation
(Hurley et al., GCN 16225), and is 7' from the center of the error

Given the spatial coincidence with the IPN localization, the lack of
archival detections, and the source fading, iPTF14aue is likely
associated with the GRB. We are submitting a Swift XRT target of
opportunity. Further observations are encouraged to confirm the
association and the nature of the candidate.

The diagram shows the
ten P48 fields in relation to the Fermi GBM 1- and 2-sigma
statistical+systematic contours, and the IPN error box.

We thank the Fermi-GBM and IPN teams for sharing their localizations
with us.
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