AstroNote 2020-107

We are carrying out the "Pan-STARRS Search for Kilonovae" which is a focused search for intrinsically faint transients, or rapidly evolving transients in galaxies which are closer than 200 Mpc in the ongoing Pan-STARRS Near-Earth Object surveys (see Smartt et al. AstroNote 2019-48 for details). 

In normal survey mode, Pan-STARRS takes 4 x 45s exposures in w, i or z each night reaching 5 sigma magnitudes of w<22, i<21 and z<20.5 in each frame (see Chambers et al. 2016, 1612.05560). 

We report the discovery of an intrinsically faint transient PS20dgq (AT2020kog) in the host galaxy NGC 6106, at a redshift of z = 0.005 or d = 26 Mpc (from NED). The transient was discovered on MJD = 58987.49 (2019-05-18.49) at mag w = 20.30 +/- 0.10. It is offset from the host by 42.7" N, 9.1" E (a projected 5.8 kpc radius from the galaxy centre). At this distance the absolute magnitude is M_w = -11.90 (assuming m-M = 32.08 and foreground extinction of  A_w = 0.12).

There exists unusual pre-rise activity in the photometry of PS20dgq up to 25 days before discovery. This activity likely rules PS20dgq out as a kilonova candidate, however, combined with the intrinsic faintness this is still a peculiar transient event. A luminous stellar outburst is possible, or a rising supernova that would become detectable with ATLAS and ZTF. Spectroscopic classification is therefore strongly encouraged. A plot of the forced photometry is attached.

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.