[vsnet-grb-info 17565] GRB 160206B: iPTF P48 Observations and Optical Transient Candidates

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18995
SUBJECT: GRB 160206B: iPTF P48 Observations and Optical Transient Candidates 
DATE:    16/02/06 18:02:12 GMT
FROM:    Leo Singer at GSFC/iPTF  <leo.p.singer at nasa.gov>

L. P. Singer (NASA/GSFC), S. B. Cenko (NASA/GSFC), M. M. Kasliwal
(Caltech), and V. Bhalerao (IUCAA) report on behalf of a larger
collaboration:

Fermi GBM detected GRB 160206B (trigger 476446756 / bn160206430) at
2016-02-06 10:19:12.43. At 10:29:40, about 10 minutes after the burst, we
began searching for optical counterparts using the Palomar 48-inch Oschin
telescope (P48).

We imaged 114 fields covering an area of 379 deg^2 and covering most of
the 2-sigma statistical+systematic region of the final Fermi GBM
localization. We estimate a 84% prior probability 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 the following optical transient candidates:

   name       RA        Dec      mag   t    Notes
----------------------------------------------------------------------------
                   Hosts with spectroscopic redshifts
----------------------------------------------------------------------------
iPTF16ca 181.162415 +45.059301 19.97 +2.39 z=0.190, host is an X-ray source
iPTF16ce 188.768138 +47.301857 20.27 +2.81 z=0.131
iPTF16ch 189.333005 +51.432720 20.70 +1.82 z=0.120
iPTF16cc 187.973175 +45.076476 19.12 +2.73 z=0.062, poor subtraction in interacting host galaxy
iPTF16cl 170.605169 +59.384422 20.12 +1.79 z=0.051
iPTF16cd 187.947490 +47.927964 19.48 +1.39 z=0.030
----------------------------------------------------------------------------
                    Hosts with photometric redshifts
----------------------------------------------------------------------------
iPTF16cg 175.872772 +50.316844 19.65 +2.30 z=0.31
iPTF16ci 180.780807 +53.977868 19.49 +1.73 z=0.27
iPTF16ck 193.756732 +57.354180 20.42 +2.93 z=0.19
iPTF16cf 197.002541 +48.632699 20.05 +2.08 z=0.13
iPTF16bx 116.788070 +22.170396 19.20 -1.32 z=0.09

Times are in hours since the GBM trigger. 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).

Further observations of the above candidates are encouraged to determine
their nature and if one of them is the optical afterglow of the GRB. We
have scheduled additional imaging of the P48 fields tonight.

The diagram http://asd.gsfc.nasa.gov/Brad.Cenko/Fermi476446756.pdf
shows the locations of our candidates and the P48 fields in relation to
the Fermi GBM 1-, 2-, and 3-sigma statistical+systematic contours.