Abstract for Proposal 096056
XMM-NuSTAR Observations of the Fastest Explosive Transients
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. 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 the recent discovery of X-rays with unprecedented properties from
the FBOTs AT2018cow, CSS161010, AT2020xnd, AT2022tsd, AT2024qfm and
AT2024wpp and continue our 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. Expanding the small number of seven
FBOTs with detected X-rays is necessary to enable population studies.
Details on Observing Strategy and Trigger Criteria
TRIGGERING CRITERIA: (i) Luminous transient with inferred Lpeak<=1d43
erg/s (or r-band < -18 mag) and blue colors at maximum light g-r<0.2
(ii) with a rapid rise time trise<13 days (iii) at d<240 Mpc or with
Fx>3e-13 erg/s/cm2. FOLLOW-UP instructions: Our coordinated XMM-NuSTAR
campaign consists of 6 epochs of observations, with the first observations
ideally acquired within 5 days of trigger, followed by observations at
+10days, +15days and +30days since trigger (20ksXMM+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.