dc.contributor.advisor Gezari, Suvi en_US dc.contributor.author HUNG, TZU-YU en_US dc.date.accessioned 2019-01-31T06:30:29Z dc.date.available 2019-01-31T06:30:29Z dc.date.issued 2018 en_US dc.identifier https://doi.org/10.13016/8tbw-pdwo dc.identifier.uri http://hdl.handle.net/1903/21572 dc.description.abstract Tidal disruption events (TDEs) refer to the scenario where a star passes within the tidal disruption sphere of a supermassive black hole (SMBH) and becomes torn apart by tidal stresses. In the classical picture, a thermal flare is expected once the bound stellar debris circularize to form an accretion disk that feeds onto the black hole. This flare of radiation provides a unique window to study the demographics of black holes within distant and quiescent galaxies that cannot be probed by other means. In addition, TDEs serve as a powerful probe of the accretion process, where the mass fallback rate can be super-Eddington for \Mbh{} $<$ a few $\times$ 10$^7$ \Msun{}. In recent years, ground-based wide-field optical surveys have successfully detected about a dozen of TDEs. Yet our knowledge of these events is still limited due to their low occurrence rate ($\approx$ 10$^{-4}$--10$^{-5}$ gal$^{-1}$ yr$^{-1}$). In the first part of this thesis, we present results from a systematic selection of TDEs in the Intermediate Palomar Transient Factory (iPTF). Our selection targets typical optically-selected TDEs: blue transients ($g-r$ $<$ 0 mag) residing in the center of resolved red galaxies that are absent of previous nuclear activity. Our photometric selection has led to discoveries of two TDEs in $\sim$4 months, iPTF16axa and iPTF16fnl, in 2016. With the most stringent criteria, we significantly reduced the contamination rate from SN Ia and AGN from 200:1 to 4.5:1. We derived a TDE rate of 1.7$^{+2.9}_{-1.3}$ $\times$ 10$^{-4}$ gal$^{-1}$ yr$^{-1}$ and forecast a discovery rate of 32$^{+41}_{-25}$ TDEs per year for ZTF. The second part of this thesis features a detailed analysis of the photometric and spectroscopic observations on iPTF16axa. We compared iPTF16axa with 11 other TDEs in the literature with well-sampled optical light curves. We concluded that most of these TDE candidates have peak luminosities confined between log(L [erg s$^{-1}$]) = 43.4--44.4, with constant temperatures of a few $\times$ 10$^4$ K during their power-law declines, implying blackbody radii on the order of ten times the tidal disruption radius, that decrease monotonically with time. For TDE candidates with hydrogen and helium emission, the high helium-to-hydrogen ratios suggest that the emission arises from high-density gas, where nebular arguments break down. In the last part of this thesis, I present statistical analyses on the Zwicky Transient Facility (ZTF) data and comments on the TDE rate from the first few months of the survey. Finally, I close this chapter with an analysis on the optical spectra of the first ZTF TDE -- AT2018zr. en_US dc.language.iso en en_US dc.title SIFTING FOR SAPPHIRES IN THE TRANSIENT SKY: THE SEARCH FOR TIDAL DISRUPTION EVENTS IN THE OPTICAL TIME DOMAIN en_US dc.type Dissertation en_US dc.contributor.publisher Digital Repository at the University of Maryland en_US dc.contributor.publisher University of Maryland (College Park, Md.) en_US dc.contributor.department Astronomy en_US dc.subject.pqcontrolled Astronomy en_US dc.subject.pquncontrolled accretion disks en_US dc.subject.pquncontrolled black hole physics en_US dc.subject.pquncontrolled survey en_US dc.subject.pquncontrolled tidal disruption events en_US
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