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

M. Nicholl*, T. Wevers, S. R. Oates, K. D. Alexander, G. Leloudas, F. Onori, A. Jerkstrand, S. Gomez, S. Campana, I. Arcavi, P. Charalampopoulos, M. Gromadzki, N. Ihanec, P. G. Jonker, A. Lawrence, I. Mandel, S. Schulze, P. Short, J. Burke, C. McCullyD. Hiramatsu, D. A. Howell, C. Pellegrino, H. Abbot, J. P. Anderson, E. Berger, P. K. Blanchard, G. Cannizzaro, T. -W. Chen, M. Dennefeld, L. Galbany, S. Gonzalez-Gaitan, G. Hosseinzadeh, C. Inserra, I. Irani, P. Kuin, T. Muller-Bravo, J. Pineda, N. P. Ross, R. Roy, S. J. Smartt, K. W. Smith, B. Tucker, L. Wyrzykowski, D. R. Young

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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 ∝ 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.
Original languageEnglish
Pages (from-to)482-504
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Volume499
Issue number1
Early online date12 Oct 2020
DOIs
Publication statusPublished - 1 Nov 2020

Keywords

  • astro-ph.HE
  • astro-ph.GA
  • astro-ph.SR

Fingerprint

Dive into the research topics of 'An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz'. Together they form a unique fingerprint.

Cite this