[vsnet-grb-info 15469] GRB 140829A: iPTF optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16758
SUBJECT: GRB 140829A: iPTF optical observations
DATE:    14/08/31 00:50:32 GMT
FROM:    Leo Singer at CIT/PTF  <lsinger at caltech.edu>

L. P. Singer (Caltech), S. B. Cenko (NASA/GSFC), D. A. Perley (Caltech),
and M. M. Kasliwal (Carnegie Observatories/Princeton), report on behalf of
the intermediate Palomar Transient Factory (iPTF) collaboration:

Fermi GBM triggered on GRB 140829A (Fermi trigger 431039250 / bn140829880)
at 2014-08-29 21:07:27.47. At 2014-08-30 03:25:48, 6.3 hours after the
burst, we began searching for optical counterparts using the Palomar
48-inch Oschin telescope (P48). We imaged 17 fields covering an area of
124 deg2, covering most of the 1-sigma statistical+systematic region of the
final Fermi GBM localization. We estimate a 61% 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 faint optical
transients.

iPTF14ejs, at r=20.15+/-0.06 mag and possibly fading by 0.2+/-0.09 mag by
8.6 hours after the burst, is coincident with the galaxy SDSS
J164214.15+500743.1. It is at the coordinates:
  RA(J2000)  =  16h 42m 14.14s (250.558918 deg)
  Dec(J2000) = +50d 07' 43.3"  (+50.128685 deg)

We acquired a spectrum of iPTF14ejs using the Low Resolution Imaging
Spectrometer (LRIS) on the Keck 10m telescope. A provisional reduction
shows broad Balmer features characteristic of an AGN at a redshift of
z=0.483, and therefore it is not a GRB afterglow.

The remaining candidates do not show any clear photometric evolution over
the course of our observations:

iPTF14ejo, at r=20.32+/-0.07 mag, is coincident with the galaxy
SDSS J173008.24+545502.8. It is at the coordinates:
  RA(J2000)  =  17h 30m 08.26s (262.534415 deg)
  Dec(J2000) = +54d 55' 04.2"  (+54.917842 deg)

iPTF14eju, at r=20.66+/-0.12 mag, is 4.8" to the southwest of an r=18.43
unresolved point source that is present in archival iPTF images. It is at
the coordinates:
  RA(J2000)  =  17h 13m 25.08s (258.354509 deg)
  Dec(J2000) = +50d 10' 04.7"  (+50.167985 deg)

iPTF14ejp, at r=20.37+/-0.09 mag, is coincident with PGC 2393059. It is at
the coordinates:
  RA(J2000)  =  16h 56m 59.87s (254.249449 deg)
  Dec(J2000) = +51d 22' 21.7"  (+51.372682 deg)

iPTF14ejw, at r=20.27+/-0.10 mag, is coincident with the galaxy
SDSS J164524.99+625127.7 . It is at the coordinates:
  RA(J2000)  =  16h 45m 24.20s (251.350842 deg)
  Dec(J2000) = +62d 51' 27.7"  (+62.857694 deg)

iPTF14ejn, at r=20.31+/-0.07 mag, is coincident with the galaxy
SDSS J172732.49+540754.0. It is at the coordinates:
  RA(J2000)  =  17h 27m 32.49s (261.885373 deg)
  Dec(J2000) = +54d 07' 54.2"  (+54.131732 deg)

iPTF14ejv, at r=20.82+/-0.20 mag, is coincident with the galaxy
SDSS J174853.28+580652.3. It is at the coordinates:
  RA(J2000)  =  17h 48m 53.26s (267.221896 deg)
  Dec(J2000) = +58d 06' 52.8"  (+58.114678 deg)

The diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi431039250.pdf
shows the locations of our candidates and the P48 fields in relation to
the Fermi GBM 1- and 2-sigma statistical+systematic contours.