{
  "bibcode": "2016GCN.19381....1S",
  "body": "S. Smartt  (Queen���s University Belfast), K. C. Chambers (IfA, Univ. of Hawaii),  \nK. Smith (QUB), M. E. Huber (IfA), D. Wright (QUB), \nH. Flewelling, E. A. Magnier, N. Primak, A. S. B. Schultz (IfA), J. Tonry, \nC. Waters, M. Willman (IfA), D. Young (QUB)\n\nFurther to the detection of a candidate cosmic neutrino, as event IceCube-160427A\n(Blaufuss et al. GCN 19363) we report Pan-STARRS1 imaging of the field and a \nsearch for optical transients. \n\nWe observed the field, entered on RA=240.57d and DEC=+9.34d (J2000) \nbeginning MJD 57508.5 UT (2016 April 30.5), which was 3.3 \ndays after the IceCube detection (2016 April 27.2) with the Pan-STARRS1\ntelescope in the i-band filter. Difference imaging with respect to the \nPan-STARRS1 3Pi stacked reference sky reached 5-sigma limiting magnitudes of \naround i~22.5. We repeated the observations on the 4 subsequent nights. \n\nSimilar to Lipunov et al. (GCN19362), we find no bright transient source\nwithin the 90% containment area of 36 arc minutes radius of the above position \n(RA=16:02:16.8, DEC=+09:20:24). We find the following 24 fainter sources\n\nEight QSOs (with SDSS spectra) are found to be significantly variable\n(the variable flux was 18.8 < i < 21.4) and are in the \nredshift range 0.345 to 2.384. \n\nSeven supernova candidates (discovery mags 20.5 < i < 22.1) were found. These\nare transient sources which have a detected candidate host galaxy, and either \noffset from the host or are coincident but not known QSO/AGN. No \ncatalogued spectroscopic redshifts of the hosts are available. \n\nA further 9 transients were found associated with faint point sources that \nare either faint Galactic variable stars or QSO variability. \n\nIn summary, there is no obvious counterpart candidate in the optical\nbrighter than i ~ 21.  Within the 90% containment field diameter of 1.2 degrees, \nwe have hit the confusion limit of the faint variable sky. While there are many \nvariable/transient candidates, there is no one object that is statistically \nrare enough it could be considered further. \n\nThe SN candidates are as follows. Six of the candidates show  flat \nlightcurves across our 5 days of monitoring, consistent with being \nSN at or after peak. One object is worth considering further :\n\nObject \t   | RA (J2000)  | DEC (J2000) | Disc Date  |  i -mag    \nPS16cgv    | 15 59 53.84 | +09 11 08.4 |  20160430  |  22.01  \nPS16cgw    | 16 00 39.69 | +09 39 21.2 |  20160430  |  21.80 \nPS16cfu    | 16 01 15.66 | +09 25 04.7 |  20160430  |  21.14 \nPS16cgx    | 16 01 18.60 | +09 51 53.1 |  20160430  |  21.84 *\nPS16cfz    | 16 02 11.96 | +09 54 07.9 |  20160430  |  21.27 \nPS16cgb    | 16 02 19.12 | +09 34 50.1 |  20160430  |  22.03\nPS16cgi    | 16 03 27.72 | +08 54 05.2 |  20160430  |  22.09\n\n\n* PS16cgx rose at by 0.4 mag over 2 days. The rise time would\nbe consistent with a type Ic supernova at z ~ 0.1 to 0.2 that \nexploded on or around 2016 April 27.2 (and possibly an off-axis GRB). \nHowever the 4th data  point shows it has peaked at i=21.5 +/- 0.1, \nand is therefore more consistent with a type Ia SN from the normal \nfield population. Spectroscopic follow-up is needed to confirm.",
  "circularId": 19381,
  "createdOn": 1462387438000,
  "email": "s.smartt@qub.ac.uk",
  "subject": "ICECUBE-160427A : Pan-STARRS imaging and optical transients in the field",
  "submitter": "Stephen Smartt at Queen's U/Belfast  <s.smartt@qub.ac.uk>",
  "eventId": "IceCube-160427A"
}