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

March 2019 • 2019MNRAS.484.1031P

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

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 < 10¹⁴ 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.

Links

• PREPRINT http://arxiv.org/abs/1808.00969
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2019MNRAS.484.1031P
• ELECTR https://doi.org/10.1093%2Fmnras%2Fsty3420
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2019MNRAS.484.1031P
• PDF http://academic.oup.com/mnras/pdf-lookup/doi/10.1093/mnras/sty3420
• DATA https://archive.gemini.edu/searchform/publication=2019MNRAS.484.1031P
• DATA https://irsa.ipac.caltech.edu/bibdata/2019/P/2019MNRAS.484.1031P.html