An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz
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Oxford Univ Press
Black hole physicsGalaxies: nucleiTransients: tidal disruption events
Nicholl, M., Wevers, T., Oates, S. R., Alexander, K. D., Leloudas, G., Onori, F., ... & Charalampopoulos, P. (2020). An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz. arXiv preprint arXiv:2006.02454. [doi:10.1093/mnras/staa2824]
SponsorshipRoyal Astronomical Society Research Fellowship; European Research Council (ERC) 320360 647208; European Commission European Commission Joint Research Centre 730980; Villum Fonden 19054; Polish NCN MAESTRO Grant 2014/14/A/ST9/00121; Polish NCN DAINA Grant 2017/27/L/ST9/03221; Israel Science Foundation 2108/18 2752/19; US-Israel Binational Science Foundation; Israeli Council forHigher Education Alon Fellowship; National Aeronautics & Space Administration (NASA) 80NSSC18K0577 NAS5-26555; European Union (EU) 842471 839090; European Union (EU) PGC2018-095317-B-C21; Portuguese Foundation for Science and Technology CRISP PTDC/FIS-AST-31546 UIDB/00099/2020; Australian Research Council FT190100574; CONICYT PFCHA/DOCTORADOBECAS CHILE 2017-72180113; NASA through the NASA Hubble Fellowship grant - Space Telescope Science Institute HST-HF2-51403.001-A; European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under ESO programmes 1103.D-0328 0104.B-0709; WilliamHerschel Telescope W19B/P7; Science & Technology Facilities Council (STFC)
At 66 Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to date, with a luminosity intermediate between the bulk of the population and the faint-and-fast event iPTF16fnl. Its proximity allowed a very early detection and triggering of multiwavelength and spectroscopic follow-up well before maximum light. The velocity dispersion of the host galaxy and fits to the TDE light curve indicate a black hole mass ≈106M , disrupting a star of ≈1M . By analysing our comprehensive UV, optical, and X-ray data, we show that the early optical emission is dominated by an outflow, with a luminosity evolution L ∝ t2, consistent with a photosphere expanding at constant velocity ( 2000 km s−1), and a line-forming region producing initially blueshifted H and He II profiles with v = 3000–10 000 km s−1. The fastest optical ejecta approach the velocity inferred from radio detections (modelled in a forthcoming companion paper from K. D. Alexander et al.), thus the same outflow may be responsible for both the fast optical rise and the radio emission – the first time this connection has been observed in a TDE. The light-curve rise begins 29 ± 2 d before maximum light, peaking when the photosphere reaches the radius where optical photons can escape. The photosphere then undergoes a sudden transition, first cooling at constant radius then contracting at constant temperature. At the same time, the blueshifts disappear from the spectrum and Bowen fluorescence lines (N III) become prominent, implying a source of far-UV photons, while the X-ray light curve peaks at ≈1041 erg s−1. Assuming that these X-rays are from prompt accretion, the size and mass of the outflow are consistent with the reprocessing layer needed to explain the large optical to X-ray ratio in this and other optical TDEs, possibly favouring accretion-powered over collision-powered outflow models.