Author(s): A. Lien, University of Maryland, Baltimore County, Baltimore, Maryland, UNITED STATES|
Institution(s): 1. University of Maryland, Baltimore County, Baltimore, MD, United States.
Contributing team(s): N. Paul M. Kuin, Kinwah Wu, Samantha Oates, Sam Emery, Jamie Kennea, Massimiliano de Pasquale, Qin Han, Peter J. Brown, Aaron Tohuvavohu, Alice Breeveld, David N. Burrows, S. Bradley Cenko, Sergio Campana, Andrew Levan, Craig Markwardt, Julian P. Osborne, Mat J. Page, Kim L. Page, Boris Sbarufatti, Michael Siegel, and Eleonora Troja
A bright transient AT2018cow was discovered on June 16, 2018 by the ATLAS wide-field survey. Its large UV brightness, rapid rise in 1-2 days, fast decay, and an initially nearly featureless spectrum are unprecedented and difficult to explain as compared to other transient sources. Here, we present analysis of the multi-wavelength observations from the Neil Gehrels Swift Observatory. The Swift observations show evidence of faint gamma-ray emission that lasts for at least 8 days. The X-ray light curve decays with a break around day 21 and has large amplitude variability. The UV-optical spectrum can be well-described by a blackbody and shows no evidence for C, N, O emission lines in the UV. We model the observations by a tidal disruption event where a small, 0.1 − 0.4 solar mass, Helium White Dwarf undergoes a fast disruption by a 10^5 – 10^6 solar mass Black Hole. In addition to a 30,000K cooling black body, a non-thermal jet is present which is responsible for the high-energy gamma-ray and X-ray emission.