AstroNote 2020-106

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 PS20dfb (AT2020kfr) in the host galaxy GALEXASC J143604.85-025300.6, at a redshift of z = 0.043 or d = 185 Mpc (from NED). The transient was discovered on MJD = 58985.42 (2020-05-16.42) at mag m_w = 21.03 +/- 0.17. There was no detection by Pan-STARRS on MJD = 58960.49 (2020-04-21.49) suggesting this is not an old supernova. It is offset from the host by 8.6" N, 9.7" W (a projected 12.0 kpc radius from the galaxy centre). At this distance, the absolute magnitude is M_w = -15.51 (assuming m-M = 36.34 and foreground extinction of A_w = 0.20). 

PS20dfb was followed up by Pan-STARRS on MJD = 58987.33 (2020-05-18.33) and observed at mag m_w = 21.13 +/- 0.15. This small change in magnitude two days after discovery rules the transient out as a kilonova candidate. However, spectroscopic classification is still encouraged. 

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.