It was first detected on June 14, 2015, located within a faint galaxy in the southern constellation Indus, and was the most luminous supernova-like object ever observed.

The most popular explanations are that it is the most luminous type I supernova (hypernova) ever observed, or a tidal disruption event around a 108 M☉ supermassive black hole.

A possible supernova was first noticed during an observation in June 2015 by ASAS-SN's twin 14-cm telescopes located at Cerro Tololo Inter-American Observatory, Chile; the team gave it the designation ASASSN-15lh.

[3] On July 24, the event formally received the supernova designation SN 2015L from the Central Bureau of Astronomical Telegrams.

[3] According to Krzysztof Stanek of Ohio State University, one of the principal investigators at ASAS-SN, "If it was in our own galaxy, it would shine brighter than the full moon; there would be no night, and it would be easily seen during the day.

Its unusual location in a relatively quiescent galaxy may offer clues for scientists to discover and observe similar events.

One model for unusually luminous supernovae involves the conversion of rotational energy from a rapidly-spinning neutron star into polar jets that heat surrounding material.

Again, the energy produced by ASASSN-15lh strains the theoretical limits of this type of explosion and the detailed properties are difficult to reproduce with a magnetar model.

[14] One known method for producing extremely large amounts of energy is the tidal disruption of objects such as stars by a supermassive black hole.

The conditions for the production of a highly luminous flare from a TDE around a black hole of the expected mass are unusual, but a rapidly-spinning Kerr black hole might be able to disrupt a star with a mass similar to the sun outside the event horizon and produce a hot accretion disc and luminous transient.

However, this usually occurs with objects much more distant than ASASSN-15lh, and there are no observations indicating the presence of a galaxy cluster suitable to produce a lensing effect.