LIGO/Virgo S190930t: ATLAS Forced photometry of ZTF19acbpqlh (AT2019rpn)

The transient ZTF19acbpqlh (AT2019rpn) was reported by Stein et al. (GCN 25899) at r = 20.02 within the 95% localisation bayestar map (LVC et al. GCN 25876). ATLAS covered this region on 6 recent epochs, and forced PSF photometry on the difference images at the position of this transient gives the following 3-sigma limiting magnitudes and two 4-sigma detections. 58752.21516 c < 18.24 58754.21109 o < 18.71 58755.35411 c < 21.00 58756.60703339205 == s190930t discovery 58756.2132 c < 19.47 58757.23448 o 19.84 +/- 0.26 58758.21185 o 19.68 +/- 0.27 All mags are AB. c = cyan filter (a g+r composite) o = orange filter (a i+r composite) Tan et al. (GCN 25916) reported r = 20.7 +/- 0.3 which could imply a significant fade, although the uncertainty is significant. Our measurements imply the transient is flat or slowly rising. Karambelkar et al (GCN 25921) give a tentative identification of broad H-alpha in their blue spectrum. Our ATLAS photometry would support their conclusion of a young, relatively faint, type II SN. But further data are required to confirm.