The fast, luminous ultraviolet transient AT2018cow: extreme supernova, or disruption of a star by an intermediate-mass black hole?

Perley, Daniel A and Mazzali, Paolo A and Yan, Lin and Cenko, S Bradley and Gezari, Suvi and Taggart, Kirsty and Blagorodnova, Nadia and Fremling, Christoffer and Mockler, Brenna and Singh, Avinash and Tominaga, Nozomu and Tanaka, Masaomi and Watson, Alan M and Ahumada, Tomas and Anupama, GC and Ashall, Chris and Becerra, Rosa L and Bersier, David and Bhalerao, Varun and Bloom, Joshua S and Butler, Nathaniel R and Copperwheat, Chris and Coughlin, Michael W and De, Kishalay and Drake, Andrew J and Duev, Dmitry A and Frederick, Sara and Jesus Gonzalez, J and Goobar, Ariel and Heida, Marianne and Ho, Anna YQ and Horst, John and Hung, Tiara and Itoh, Ryosuke and Jencson, Jacob E and Kasliwal, Mansi M and Kawai, Nobuyuki and Khanam, Tanazza and Kulkarni, Shrinivas R and Kumar, Brajesh and Kumar, Harsh and Kutyrev, Alexander S and Lee, William H and Maeda, Keiichi and Mahabal, Ashish and Murata, Katsuhiro L and Neill, James D and Ngeow, Chow-Choong and Penprase, Bryan and Pian, Elena and Quimby, Robert and Ramirez-Ruiz, Enrico and Richer, Michael G and Roman-Zuniga, Carlos G and Sahu, DK and Srivastav, Shubham and Socia, Quentin and Sollerman, Jesper and Tachibana, Yutaro and Taddia, Francesco and Tinyanont, Samaporn and Troja, Eleonora and Ward, Charlotte and Wee, Jerrick and Yu, Po-Chieh (2019) The fast, luminous ultraviolet transient AT2018cow: extreme supernova, or disruption of a star by an intermediate-mass black hole? In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 484 (1). pp. 1031-1049.

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Abstract

Wide-field optical surveys have begun to uncover large samples of fast (t(rise) less than or similar to 5 d), luminous (M-peak < 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 AT 2018cow (ATLAS 18qqn), the first fast-luminous optical transient to be found in real time at low redshift. Our first spectra (<2 days after discovery) are entirely featureless. A very broad absorption feature suggestive of near-relativistic velocities develops between 3 and 8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R < 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, AT 2018cow 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.

Item Type:	Journal Article
Publication:	MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Publisher:	OXFORD UNIV PRESS
Additional Information:	Copyright of this article belongs to OXFORD UNIV PRESS
Keywords:	Black hole; stars; supernovae: general; supernova: individual: AT2018cow
Department/Centre:	Division of Physical & Mathematical Sciences > Joint Astronomy Programme
Date Deposited:	20 May 2019 07:43
Last Modified:	20 May 2019 07:43
URI:	http://eprints.iisc.ac.in/id/eprint/62294

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