An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz Nicholl, M. Galbany González, Lluis Black hole physics Galaxies: nuclei Transients: tidal disruption events We thank the anonymous referee for their many suggestions that improved this paper. We thank Miguel Perez-Torres for helpful discussions. MN is supported by a Royal Astronomical Society Research Fellowship. TW is funded in part by European Research Council grant 320360 and by European Commission grant 730980. PGJ and GC acknowledge support from European Research Council Consolidator Grant 647208. GL and PC are supported by a research grant (19054) from Villum Fonden. MG is supported by the Polish NCN MAESTRO Grant 2014/14/A/ST9/00121. NI is partially supported by Polish NCN DAINA Grant 2017/27/L/ST9/03221. IA is a CIFAR Azrieli Global Scholar in the Gravity and the Extreme Universe Program and acknowledges support from that program, from the Israel Science Foundation (grant numbers 2108/18 and 2752/19), from the United States-Israel Binational Science Foundation (BSF), and from the Israeli Council forHigher Education Alon Fellowship. JB, DH, and CP were supported by NASA Grant 80NSSC18K0577. TWCacknowledges the EU Funding underMarie Sklodowska-Curie grant agreement No. 842471. LG was funded by the European Union's Horizon 2020 Framework Programme under theMarie Sklodowska-Curie grant agreement No. 839090. Thiswork has been partially supported by the Spanish grant PGC2018-095317-B-C21 within the European Funds for Regional Development (FEDER). SGGacknowledges support by FCT under Projects CRISP PTDC/FIS-AST-31546 and UIDB/00099/2020. IM is a recipient of the Australian Research Council Future Fellowship FT190100574. TMBwas funded by the CONICYT PFCHA/DOCTORADOBECAS CHILE/2017-72180113. KDA acknowledges support provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51403.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This work is based on data collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under ESO programmes 1103.D-0328 and 0104.B-0709 and as part of ePESSTO+(the advanced Public ESO Spectroscopic Survey for Transient Objects Survey), observations from the Las Cumbres Observatory network, the 6.5 meterMagellan Telescopes located at Las Campanas Observatory, Chile, the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution and the WilliamHerschel Telescope (programme W19B/P7). Swift data were supplied by the UK Swift Science Data Centre at the University of Leicester. The Liverpool Telescope andWilliam Herschel Telescope are operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. 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. 2020-12-22T12:04:10Z 2020-12-22T12:04:10Z 2020-11 journal article 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] http://hdl.handle.net/10481/65105 10.1093/mnras/staa2824 eng info:eu-repo/grantAgreement/EC/H2020/Marie Sklodowska-Curie 839090 http://creativecommons.org/licenses/by-nc-nd/3.0/es/ open access Atribución-NoComercial-SinDerivadas 3.0 España Oxford Univ Press