Abstract for Proposal 084355

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.

Details on Observing Strategy and Trigger Criteria
TRIGGERING CRITERIA: (i) Luminous transient with inferred Lpeak>=1d43 erg/s (or V-band <-19) and blue colors at maximum light B-V<0.2 (ii) with a rapid rise time trise<13 days (iii) at d<240 Mpc. FOLLOW-UP instructions: Our coordinated XMM-NuSTAR campaign consists of a maximum of four epochs at 5 ,10,15 and 30 days (20 ks XMM+25 ks NuSTAR for the first two epochs and 20 ks XMM + 40 ks NuSTAR for the second two epochs), followed by two 40ks-epochs of deep XMM observations at late times t~90 and ~200 days. The fourth NuSTAR observation will be carried out only in the case of detection in one previous epoch.