AT2018cow

AT2018cow (aka SN 2018cow or informally, the cow) is an optical transient detected on June 16, 2018 in the galaxy, CGCG 137-068. It is classified as a supernova but with unusual characteristics: it is a fast blue optical transient (FBOT) that shows at least an order-of-magnitude more energy than a typical supernova, and the mechanism and type of progenitor are open to question. There are ongoing attempts to explain it, some possibilities being some neutron star phenomenon, or the formation of a black hole.

AT2018cow has been taken as a prototype for subsequent transients that also show its interesting characteristics. Because of the current interest in these, the term cow is also currently used informally for such transients. Among them:

• AT2018lug (ZTF18abvkwla, aka the koala, for "kwla").
• AT2020xnd (ZTF20acigmel, aka the camel, for "gmel").

Note that the strings "cow", "lug", etc. are supernova-designator suffixes indicating which of the year's reported supernovae candidates: (based on the order of reporting the transient: by my calculation, "cow" is transient number 2441 for the year). Other years will have their own unrelated "cow".