The fast, luminous ultraviolet transient AT2018cow: extreme supernova, or disruption of a star by an intermediate-mass black hole?. Issue 1 (22nd December 2018)

• Record Type: Journal Article
• Authors: Perley, Daniel A; Mazzali, Paolo A; Yan, Lin; Cenko, S Bradley; Gezari, Suvi; Taggart, Kirsty; Blagorodnova, Nadia; Fremling, Christoffer; Mockler, Brenna; Singh, Avinash; Tominaga, Nozomu; Tanaka, Masaomi; Watson, Alan M; Ahumada, Tomás; Anupama, G C; Ashall, Chris; Becerra, Rosa L; Bersier, David; Bhalerao, Varun; Bloom, Joshua S; Butler, Nathaniel R; Copperwheat, Chris; Coughlin, Michael W; De, Kishalay; Drake, Andrew J; Duev, Dmitry A; Frederick, Sara; González, J Jesús; Goobar, Ariel; Heida, Marianne; Ho, Anna Y Q; Horst, John; Hung, Tiara; Itoh, Ryosuke; Jencson, Jacob E; Kasliwal, Mansi M; Kawai, Nobuyuki; Khanam, Tanazza; Kulkarni, Shrinivas R; Kumar, Brajesh; Kumar, Harsh; Kutyrev, Alexander S; Lee, William H; Maeda, Keiichi; Mahabal, Ashish; Murata, Katsuhiro L; Neill, James D; Ngeow, Chow-Choong; Penprase, Bryan; Pian, Elena; Quimby, Robert; Ramirez-Ruiz, Enrico; Richer, Michael G; Román-Zúñiga, Carlos G; Sahu, D K; Srivastav, Shubham; Socia, Quentin; Sollerman, Jesper; Tachibana, Yutaro; Taddia, Francesco; Tinyanont, Samaporn; Troja, Eleonora; Ward, Charlotte; Wee, Jerrick; Yu, Po-Chieh;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 484:Issue 1(2019)
• Page Start: 1031
• Page End: 1049
• Publication Date: 2018-12-22
• Subjects: Black hole -- stars -- supernovae: general -- supernova: individual: AT2018cow; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty3420
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Wide-field optical surveys have begun to uncover large samples of fast ( t rise ≲ 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.