The Cow: discovery of a luminous, hot and rapidly evolving transient

Understand

We present the ATLAS discovery and initial analysis of the first 18 days of the unusual transient event, ATLAS18qqn/AT2018cow.

• It is characterized by a high peak luminosity ($\sim$1.7 $\times$ 10$^{44}$ erg s$^{-1}$), rapidly evolving light curves ($>$5 mag rise to peak in $\sim$3.5 days), and hot blackbody spectra, peaking at $\sim$27000 K that are relatively featureless and unchanging over the first two weeks.
• The bolometric light curve cannot be powered by radioactive decay under realistic assumptions.
• The detection of high-energy emission may suggest a central engine as the powering source.