The First Tidal Disruption Flare in ZTF: From Photometric Selection to Multi-wavelength Characterization
Cenko, S. Bradley; Riddle, Reed; Rusholme, Ben; Sollerman, Jesper; van Velzen, Sjoert; Gezari, Suvi; Roth, Nathaniel; Frederick, Sara; Ward, Charlotte; Hung, Tiara; Stein, Robert; Blagorodnova, Nadejda; Bellm, Eric C.; Brinnel, Valery; Dekany, Richard; Fremling, Christoffer; Giomi, Matteo; Golkhou, V. Zach; Graham, Matthew J.; Kasliwal, Mansi M.; Kulkarni, Shrinivas R.; Kupfer, Thomas; Laher, Russ R.; Mahabal, Ashish; Masci, Frank J.; Miller, Adam A.; Nordin, Jakob; van Santen, Jakob; Soumagnac, Maayane T.; Neill, James D.; Kara, Erin; Miller-Jones, James C. A.; Yan, Lin; Rigault, Mickael; Fender, Rob; Bright, Joe; Huppenkothen, Daniela; Ofek, Eran; Tachibana, Yutaro; Canella, Chris
United States, Australia, United Kingdom, Israel, Sweden, Germany, France, Japan
Abstract
We present Zwicky Transient Facility (ZTF) observations of the tidal disruption flare AT2018zr/PS18kh reported by Holoien et al. and detected during ZTF commissioning. The ZTF light curve of the tidal disruption event (TDE) samples the rise-to-peak exceptionally well, with 50 days of g- and r-band detections before the time of maximum light. We also present our multi-wavelength follow-up observations, including the detection of a thermal (kT ≈ 100 eV) X-ray source that is two orders of magnitude fainter than the contemporaneous optical/UV blackbody luminosity, and a stringent upper limit to the radio emission. We use observations of 128 known active galactic nuclei (AGNs) to assess the quality of the ZTF astrometry, finding a median host-flare distance of 0.″2 for genuine nuclear flares. Using ZTF observations of variability from known AGNs and supernovae we show how these sources can be separated from TDEs. A combination of light-curve shape, color, and location in the host galaxy can be used to select a clean TDE sample from multi-band optical surveys such as ZTF or the Large Synoptic Survey Telescope.