Papers › The Tidal Disruption Event AT 2018hyz II: Light Curve Modeling of a Partially Disrupted Star
The Tidal Disruption Event AT 2018hyz II: Light Curve Modeling 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, Tomás E. Müller Bravo, Locke Patton, Giacomo Terreran
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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 days after bolometric peak, followed by a flattening beyond 250 days. The light curve shows an excess bump in the UV about 50 days after bolometric peak lasting for at least 100 days, which may be related to an outflow. We detect a constant X-ray source present for at least 86 days. 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 Γ= 0.8. A thermal X-ray model is unable to account for photons > 1 keV, while the radio non-detection favors 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 M_⊙ partially disrupting a $0.1$ M_⊙ star (stripping a mass of ∼0.01 M_⊙ for the inferred impact parameter, β=0.6). The low optical depth implied by the small debris mass may explain how we are able to see hydrogen emission with disk-like line profiles in the spectra of AT 2018hyz (see our companion paper, Short et al.~2020).
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