The Fast, Luminous Ultraviolet Transient AT2018cow: Extreme Supernova, or Disruption of a Star by an Intermediate-Mass Black Hole?
Creators: name: Perley, Daniel A.
name: Mazzali, Paolo A.
name: Yan, Lin
name: Cenko, S. Bradley
name: Gezari, Suvi
name: Taggart, Kirsty
name: Blagorodnova, Nadia
name: Fremling, Christoffer
name: Mockler, Brenna
name: Singh, Avinash
name: Tominaga, Nozomu
name: Tanaka, Masaomi
name: Watson, Alan M.
name: Ahumada, Tomás
name: Anupama, G. C.
name: Ashall, Chris
name: Becerra, Rosa L.
name: Bersier, David
name: Bhalerao, Varun
name: Bloom, Joshua S.
name: Butler, Nathaniel R.
name: Copperwheat, Chris
name: Coughlin, Michael W.
name: De, Kishalay
name: Drake, Andrew J.
name: Duev, Dmitry A.
name: Frederick, Sara
name: González, J. Jesús
name: Goobar, Ariel
name: Heida, Marianne
name: Ho, Anna Y. Q.
name: Horst, John
name: Hung, Tiara
name: Itoh, Ryosuke
name: Jencson, Jacob E.
name: Kasliwal, Mansi M.
name: Kawai, Nobuyuki
name: Kulkarni, Shrinivas R.
name: Kumar, Brajesh
name: Kumar, Harsh
name: Kutyrev, Alexander S.
name: Khanam, Tanazza
name: Lee, William H.
name: Maeda, Keiichi
name: Mahabal, Ashish
name: Murata, Katsuhiro L.
name: Neill, James D.
name: Ngeow, Chow-Choong
name: Penprase, Bryan
name: Pian, Elena
name: Quimby, Robert
name: Ramirez-Ruiz, Enrico
name: Richer, Michael
name: Román-Zúñiga, Carlos G.
name: Srivastava, Shubham
name: Socia, Quentin
name: Sollerman, Jesper
name: Tachibana, Yutaro
name: Taddia, Francesco
name: Tinyanont, Samaporn
name: Troja, Eleonora
name: Ward, Charlotte
name: Wee, Jerrick
Publisher: name: arXiv
Year: 2018
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Wide-field optical surveys have begun to uncover large samples of fast (t_rise &lt; 5d), luminous (M_peak &lt; -18), blue transients. While commonly attributed to the breakout of a supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered detailed investigation of their properties. We present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT2018cow (ATLAS18qqn), the first fast-luminous optical transient to be found in real time at low redshift. Our first spectra (&lt;2 days after discovery) are entirely featureless. A very broad absorption feature suggestive of near-relativistic velocities develops between 3-8 days, then disappears. Broad emission features of H and He develop after &gt;10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R&lt;10^14 cm after 1 month). This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass black hole, although this would require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.
description: Corrected Figure 8 / Table 4 to use final fits. Includes machine-readable photometry table (hopefully for real this time)