The Tidal Disruption Event at 2018hyz II: Light-curve modelling of a partially disrupted star

Sebastian Gomez*, Matt Nicholl, Philip Short, Raffaella Margutti, Kate D. Alexander, Peter K. Blanchard, Edo Berger, Tarraneh Eftekhari, Steve Schulze, Joseph Anderson, Iair Arcavi, Ryan Chornock, Philip S. Cowperthwaite, Lluís Galbany, Laura J. Herzog, Daichi Hiramatsu, Griffin Hosseinzadeh, Tanmoy Laskar, Tomas E. Müller Bravo, Locke PattonGiacomo Terreran

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


AT 2018hyz (= ASASSN-18zj) is a tidal disruption event (TDE) located in the nucleus of a quiescent E+A galaxy at a redshift of z = 0.04573, first detected by the All-Sky Automated Survey for Supernovae (ASAS-SN). We present optical+UV photometry of the transient, as well as an X-ray spectrum and radio upper limits. The bolometric light curve of AT 2018hyz is comparable to other known TDEs and declines at a rate consistent with a t-5/3 at early times, emitting a total radiated energy of E = 9 × 1050 erg. An excess bump appears in the UV light curve about 50 d after bolometric peak, followed by a flattening beyond 250 d. We detect a constant X-ray source present for at least 86 d. The X-ray spectrum shows a total unabsorbed flux of ~4 × 10-14 erg cm -2 s-1 and is best fit by a blackbody plus power-law model with a photon index of r = 0.8. A thermal X-ray model is unable to account for photons > 1 keV, while a radio non-detection favours inverse-Compton scattering rather than a jet for the non-thermal component. We model the optical and UV light curves using the Modular Open-Source Fitter for Transients (MOSFiT) and find a best fit for a black hole of 5.2 × 106 M0 disrupting a 0.1 M0 star; the model suggests the star was likely only partially disrupted, based on the derived impact parameter of ß = 0.6. The low optical depth implied by the small debris mass may explain how we are able to see hydrogen emission with disc-like line profiles in the spectra of AT2018hyz (see our companion paper).

Original languageEnglish (US)
Pages (from-to)1925-1934
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Sep 1 2020


  • Black hole physics
  • Galaxies: nuclei

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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