[vsnet-grb-info 18312] IceCube-160731A: iPTF P48 Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19760
SUBJECT: IceCube-160731A: iPTF P48 Observations
DATE:    16/08/04 00:11:38 GMT
FROM:    Leo Singer at GSFC/iPTF  <leo.p.singer at nasa.gov>

L. P. Singer (NASA/GSFC), M. M. Kasliwal (Caltech), Varun Bhalerao (IUCAA),
Anna Ho (Caltech), Tom Barlow (Caltech), S. B. Cenko (NASA/GSFC),
E. O. Ofek (Weizmann), N. Strotjohann (DESY), A. Franckowiak (DESY),
M. Kowalski (DESY), and G. Tesic (PSU) report on behalf of the
Intermediate Palomar Transient Factory (iPTF) collaboration:

Following the detection and updated localization of the cosmic neutrino
candidate IceCube-160731A
(http://gcn.gsfc.nasa.gov/notices_amon/6888376_128290.amon), we began
searching for optical counterparts using the Palomar 48-inch Oschin
telescope (P48) on 2016-07-31 at 05:22 UT, 3.5 hours after the trigger.

We imaged one field covering an area of 7.1 deg^2 to a limiting magnitude
of R=19.1--19.7. Unfortunately, the EHE localization coincides with an
inoperable CCD. Sifting through candidate variable sources using image
subtraction and standard iPTF vetting procedures, we do not detect any
optical transients close to the IceCube error circle. Two optical
transient candidates are found at 1.1 and 2.0 deg from the neutrino
candidate position:

   name       RA        Dec     sep  mag   t
-----------------------------------------------
iPTF16elf 213.555124 -0.894361 1.1 17.25 3.5
iPTF16elg 212.640918 -0.988094 2.0 18.71 3.75

The two transients are positionally consistent with the nuclei of their
respective host galaxies, CGCG 018-088 at z=0.038 and SDSS
J141033.84-005918.0 at z=0.054.

Positions are in J2000. Separations are in degrees and relative to the
best-estimate IceCube position (214.5440d -0.3347d). Magnitudes are in the
Mould R filter and in the AB system, calibrated with respect to point
sources in SDSS as described in Ofek et al. (2012,
http://dx.doi.org/10.1086/664065). Times are in hours since the IceCube
trigger.

The diagram http://asd.gsfc.nasa.gov/Leo.Singer/iptf/IceCube-160731.pdf
shows the P48 field in relation to the IceCube 1-sigma error circles.