SIFTING FOR SAPPHIRES: SYSTEMATIC SELECTION OF TIDAL DISRUPTION EVENTS IN iPTF

T Hung; S Gezari; S B Cenko; S van Velzen; N Blagorodnova; Lin Yan; S R Kulkarni; R Lunnan; T Kupfer; G Leloudas; A K H Kong; P E Nugent; C Fremling; Russ R Laher; F J Masci; Y Cao; R Roy; T Petrushevska

doi:10.3847/1538-4365/aad8b1

SIFTING FOR SAPPHIRES: SYSTEMATIC SELECTION OF TIDAL DISRUPTION EVENTS IN iPTF

Astrophys J Suppl Ser. 2018 Oct;238(2):15. doi: 10.3847/1538-4365/aad8b1. Epub 2018 Sep 27.

Authors

T Hung¹, S Gezari^{1

2}, S B Cenko^{2

3}, S van Velzen^{2

4}, N Blagorodnova⁵, Lin Yan^{6

7}, S R Kulkarni⁵, R Lunnan⁸, T Kupfer⁵, G Leloudas⁹, A K H Kong¹⁰, P E Nugent^{11

12}, C Fremling⁵, Russ R Laher⁷, F J Masci⁷, Y Cao^{13

14}, R Roy⁸, T Petrushevska¹⁵

Affiliations

¹ Department of Astronomy, University of Maryland, College Park, MD 20742, USA.
² Joint Space-Science Institute, University of Maryland, College Park, MD 20742, USA.
³ NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771, USA.
⁴ Department of Physics, New York University, NY 10003, USA.
⁵ Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA.
⁶ Caltech Optical Observatories, Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA.
⁷ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA.
⁸ The Oskar Klein Centre & Department of Astronomy, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden.
⁹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, 2100 Copenhagen, Denmark.
¹⁰ Institute of Astronomy, National Tsing Hua University, No. 101, Section 2, Kuang-Fu Road, Hsinchu, 30013, Taiwan.
¹¹ Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA.
¹² Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50B-4206, Berkeley, CA 94720, USA.
¹³ Department of Astronomy, University of Washington, Box 351580, U.W., Seattle, WA 98195-1580, USA.
¹⁴ eScience Institute, University of Washington, Box 351570, U.W., Seattle, WA 98195-1580, USA.
¹⁵ Oskar Klein Centre, Department of Physics, Stockholm University, SE 106 91 Stockholm, Sweden.

Abstract

We present results from a systematic selection of tidal disruption events (TDEs) in a wide-area (4800 deg²), g + R band, Intermediate Palomar Transient Factory (iPTF) experiment. Our selection targets typical optically-selected TDEs: bright (>60% flux increase) and blue transients residing in the center of red galaxies. Using photometric selection criteria to down-select from a total of 493 nuclear transients to a sample of 26 sources, we then use follow-up UV imaging with the Neil Gehrels Swift Telescope, ground-based optical spectroscopy, and light curve fitting to classify them as 14 Type Ia supernovae (SNe Ia), 9 highly variable active galactic nuclei (AGNs), 2 confirmed TDEs, and 1 potential core-collapse supernova. We find it possible to filter AGNs by employing a more stringent transient color cut (g - r < -0.2 mag); further, UV imaging is the best discriminator for filtering SNe, since SNe Ia can appear as blue, optically, as TDEs in their early phases. However, when UV-optical color is unavailable, higher precision astrometry can also effectively reduce SNe contamination in the optical. Our most stringent optical photometric selection criteria yields a 4.5:1 contamination rate, allowing for a manageable number of TDE candidates for complete spectroscopic follow-up and real-time classification in the ZTF era. We measure a TDE per galaxy rate of ${1.7}_{- 1.3}^{+ 2.9} \times 10^{- 4} {gal}^{- 1} {yr}^{- 1}$ (90% CL in Poisson statistics). This does not account for TDEs outside our selection criteria, thus may not reflect the total TDE population, which is yet to be fully mapped.

Keywords: accretion; accretion disks; black hole physics; galaxies: nuclei; ultraviolet: general.