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GCN Circular 18859

Subject
GRB 160113A: iPTF P48 Observations and Optical Transient Candidates
Date
2016-01-13T20:43:09Z (8 years ago)
From
Leo Singer at GSFC/iPTF <leo.p.singer@nasa.gov>
L. P. Singer (NASA/GSFC), V. Bhalerao (IUCAA), S. B. Cenko (NASA/GSFC),
and M. M. Kasliwal (Carnegie) report on behalf of a larger collaboration:

Fermi GBM detected GRB 160113A (trigger 474370354 / bn160113398) at
2016-01-13 09:32:30.52. At 10:31:39, about 1 hour after the burst, we
began searching for optical counterparts using the Palomar 48-inch Oschin
telescope (P48).

We imaged 18 fields covering an area of 133 deg^2 in the 1-sigma
statistical+systematic region of the final Fermi GBM localization. We
estimate a 78% 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
----------------------------------------------------------------------------
                                Hostless
----------------------------------------------------------------------------
iPTF15flo 192.718034 +12.070614 20.29 1.99
iPTF15fls 187.113722  +7.078087 20.59 2.42 near elliptical galaxy at z=0.175
----------------------------------------------------------------------------
                   Hosts with spectroscopic redshifts
----------------------------------------------------------------------------
iPTF15flq 179.356225 +11.915619 20.02 2.10 z=0.165
iPTF15flm 191.925125 +13.140841 19.99 1.82 z=0.155
iPTF15fly 180.870452 +13.440016 19.41 2.10 z=0.090
iPTF15fln 192.218146 +15.660583 20.23 1.88 z=0.081, possibly fading
iPTF15flp 181.050555 +11.765386 19.28 1.52 z=0.296, BL Lac (Veron+ 2010)
----------------------------------------------------------------------------
                    Hosts with photometric redshifts
----------------------------------------------------------------------------
iPTF15flk 184.180492 +13.204215 20.66 1.58 z=0.382
iPTF15flr 181.775607  +9.400882 19.03 2.19 z=0.087
----------------------------------------------------------------------------
                           Possibly stellar
----------------------------------------------------------------------------
iPTF15flx 181.613083 +13.008351 20.33 1.52

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).

We have scheduled all of the above sources for multi-band photometry on
the robotic Palomar 60" telescope (P60) tonight. We have requested Swift
target-of-opportunity observations of iPTF15flo.

Further observations of the above candidates, particularly iPTF15flo and
iPTF15fls, are encouraged to determine their nature and if one of them is
the optical afterglow of the GRB.

The diagram http://asd.gsfc.nasa.gov/Leo.Singer/Fermi474370354.pdf
shows the locations of our candidates and the P48 fields in relation to
the Fermi GBM 1- and 2-sigma statistical+systematic contours.
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