XMM-NuSTAR Observations of Rapid, Luminous and Blue Stellar Explosions

We propose an in-depth X-ray study of fast blue optical transients (FBOTs), a new class of transients with luminosities and time scales that challenge traditional SN models. Alternative scenarios include a failed SN of a stripped star, He-shell detonation on a white dwarf, and a SN shock breaking through a dense medium. FBOTs have mostly been studied in the optical/UV regime, which is of thermal origin and it is not sensitive to the nature of the underlying energy source. Here we propose to capitalize on our recent discovery of X-rays from the FBOT AT2018cow with unprecedented properties, and start the first broad-band X-ray monitoring campaign of FBOTs. The primary goal is to test for the presence of engines driving the explosions and constrain their nature.