@article{e7903ca9306447f8b7c065d4a51fe644,
title = "The tidal disruption event AT2017eqx: Spectroscopic evolution from hydrogen rich to poor suggests an atmosphere and outflow",
abstract = "We present and analyse a new tidal disruption event (TDE), AT2017eqx at redshift z = 0.1089, discovered by Pan-STARRS and ATLAS. The position of the transient is consistent with the nucleus of its host galaxy; the spectrum shows a persistent blackbody temperature T≿ 20 000 K with broad H I and He II emission; and it peaks at a blackbody luminosity of L ≈ 1044 erg s−1. The lines are initially centred at zero velocity, but by 100 d, the H I lines disappear while the He II develops a blueshift of ≿ 5000 km s−1. Both the early- and late-time morphologies have been seen in other TDEs, but the complete transition between them is unprecedented. The evolution can be explained by combining an extended atmosphere, undergoing slow contraction, with a wind in the polar direction becoming visible at late times. Our observations confirm that a lack of hydrogen a TDE spectrum does not indicate a stripped star, while the proposed model implies that much of the diversity in TDEs may be due to the observer viewing angle. Modelling the light curve suggests AT2017eqx resulted from the complete disruption of a solar-mass star by a black hole of ∼106.3 M☉. The host is another Balmer-strong absorption galaxy, though fainter and less centrally concentrated than most TDE hosts. Radio limits rule out a relativistic jet, while X-ray limits at 500 d are among the deepest for a TDE at this phase.",
author = "M. Nicholl and Blanchard, {P. K.} and E. Berger and S. Gomez and R. Margutti and Alexander, {K. D.} and J. Guillochon and J. Leja and R. Chornock and B. Snios and K. Auchettl and Bruce, {A. G.} and P. Challis and D{\textquoteright}Orazio, {D. J.} and Drout, {M. R.} and T. Eftekhari and Foley, {R. J.} and O. Graur and Kilpatrick, {C. D.} and A. Lawrence and Piro, {A. L.} and C. Rojas-Bravo and Ross, {N. P.} and P. Short and Smartt, {S. J.} and Smith, {K. W.} and B. Stalder",
note = "Funding Information: We thank an anonymous referee for many helpful comments that improved this paper. Thanks to Yuri Beletsky for IMACS observing, Jabran Zahid for help with the galaxy analysis, Jorge Anais, Jaime Vargas, Abdo Campillay, and Nahir Mu{\~n}oz Elgueta for Swope observing, and Dave Coulter for writing the Swope scheduling software. We also thank Joel Aycock, Percy Gomez, and Yen-Chen Pan for assistance with Keck/LRIS observations. MN is supported by a Royal Astronomical Society Research Fellowship. The Berger Time-Domain Group is supported in part by National Science Foundation grant AST-1714498 and NASA grant NNX15AE50G. Funding Information: We thank an anonymous referee for many helpful comments that improved this paper. Thanks to Yuri Beletsky for IMACS observing, Jabran Zahid for help with the galaxy analysis, Jorge Anais, Jaime Vargas, Abdo Campillay, and Nahir Mu?oz Elgueta for Swope observing, and Dave Coulter for writing the Swope scheduling software. We also thank Joel Aycock, Percy Gomez, and Yen-Chen Pan for assistance with Keck/LRIS observations. MN is supported by a Royal Astronomical Society Research Fellowship. The Berger Time-Domain Group is supported in part by National Science Foundation grant AST-1714498 and NASA grant NNX15AE50G. We acknowledge Chandra Award 20700239. KDA acknowledges NASA Hubble Fellowship grant HST-HF2-51403.001. ATLAS acknowledges NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575. SJS acknowledges STFC Grants ST/P000312/1 and ST/N002520/1. OG and JL are supported by NSF Astronomy and Astrophysics Fellowships under awards AST-1602595 and AST-1701487. The UCSC team is supported in part by NASA grant NNG17PX03C, NSF grant AST-1518052, the Gordon & Betty Moore Foundation, the Heising-Simons Foundation, and by a fellowship from the David and Lucile Packard Foundation to RJF. Data were obtained via the Swift archive, the Smithsonian Astrophysical Observatory OIR Data Center, the MMT Observatory of the Smithsonian Institution, and the University of Arizona, and Las Campanas Observatory. NRAO is a facility of the NSF operated by Associated Universities, Inc. ATLAS products are made possible by the University of Hawaii, Queen?s University Belfast, the Space Telescope Science Institute, and the South African Astronomical Observatory. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Funding Information: We acknowledge Chandra Award 20700239. KDA acknowledges NASA Hubble Fellowship grant HST-HF2-51403.001. ATLAS acknowledges NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575. SJS acknowledges STFC Grants ST/P000312/1 and ST/N002520/1. OG and JL are supported by NSF Astronomy and Astrophysics Fellowships under awards AST-1602595 and AST-1701487. The UCSC team is supported in part by NASA grant NNG17PX03C, NSF grant AST-1518052, the Gordon & Betty Moore Foundation, the Heising-Simons Foundation, and by a fellowship from the David and Lucile Packard Foundation to RJF. Data were obtained via the Swift archive, the Smithsonian Astrophysical Observatory OIR Data Center, the MMT Observatory of the Smithsonian Institution, and the University of Arizona, and Las Campanas Observatory. NRAO is a facility of the NSF operated by Associated Universities, Inc. ATLAS products are made possible by the University of Hawaii, Queen{\textquoteright}s University Belfast, the Space Telescope Science Institute, and the South African Astronomical Observatory. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Publisher Copyright: {\textcopyright} 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.",
year = "2019",
month = sep,
day = "11",
doi = "10.1093/mnras/stz1837",
language = "English (US)",
volume = "488",
pages = "1878--1893",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "2",
}