AstroNote 2019-48

We introduce a focused search for any intrinsically faint transients, or rapidly evolving transients in galaxies which are closer than 200 Mpc in the ongoing Pan-STARRS Near Earth Object surveys. In normal survey mode, 4 x 45s exposures in w, i or z are taken reaching each night reaching 5 sigma magnitudes of w<22, i<21 and z<20.5 (see Chambers et al. 2016, 1612.05560).

The main goal is to highlight transients that may be kilonova candidates and are in the absolute magnitude range from approximately -10 to -15 (with or without a gravitational wave trigger). This magnitude range brackets published models of r-process powered kilonovae and the peak magnitude of AT2017gfo. We caution that these will mostly be sub-luminous or old supernovae, reddened supernovae, giant eruptions of luminous blue variables , or bright classical novae, given the relative rate of such events compared to the rarity of kilonovae. However we encourage spectroscopic classification or photometric follow-up (to identify any fast fading) of these candidates. 

In the context of this "Pan-STARRS search for kilonovae", we report the discovery of an intrinsically faint transient on MJD 58680.60 == 2019-07-16.60, at z = 19.92 +/- 0.07. PS19dtj (AT2019lkf) is offset by 5.90 arcsec north, 13.04 arcsec east from UGC 12798, which is at z = 0.018 or d = 68 Mpc (from NED), implying an absolute magnitude of M = -14.4 (assuming m-M = 34.2 and A_z = 0.1).

Information on all objects discovered by the "Pan-STARRS search for kilonovae" will be made available at http://star.pst.qub.ac.uk/ps1threepi/. We will release AstroNotes for all these candidates and encourage spectroscopic classification or photometric follow-up.  A finder is attached. 

These discoveries are a byproduct of the Pan-STARRS NEO survey observations supported by the NASA Grants, including No. NNX14AM74G issued through the SSO Near Earth Object Observations Program.