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An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz

Nicholl, M; Wevers, T; Oates, SR; Alexander, KD; Leloudas, G; Onori, F; Jerkstrand, A; ... Young, DR; + view all (2020) An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz. Monthly Notices of the Royal Astronomical Society , 499 (1) pp. 482-504. 10.1093/mnras/staa2824. Green open access

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Abstract

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 ≈106 M, disrupting a star of ≈1 M. 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 ∝ t 2, 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.

Type: Article
Title: An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/staa2824
Publisher version: http://dx.doi.org/10.1093/mnras/staa2824
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: black hole physics, galaxies: nuclei, transients: tidal disruption events, SUPERMASSIVE BLACK-HOLES, X-RAY, SPECTROSCOPIC EVOLUTION, SPECTRAL EVOLUTION, DISC FORMATION, FOLLOW-UP, EMISSION, GALAXIES, MASSES, CANDIDATE
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10117088
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