Abstract for Proposal 096349
Unmasking the central engine in a Cow-like transient with XMM, VLT, CXO and HST
Luminous Fast Blue Optical Transients (LFBOTs) are characterised by
luminous multi-wavelength emission, blue colours and rapid evolution,
inconsistent with regular supernovae (SNe). Although the number of LFBOTs
is growing thanks to high-cadence, deep and wide-field photometric
surveys, detailed studies of individual events are lacking. These are
necessary to understand their progenitors and power sources. We propose
a joint programme, utilising XMM-Newton and VLT/X-Shooter, to firmly
identify and characterise a single LFBOT in detail. Our proposed X-ray
timing and monitoring observations, spectroscopic classifications and deep
imaging represent a rich dataset that will provide new insight into the
central engine of a LFBOT, at a level unmatched since the prototypical
event AT2018cow.
Details on Observing Strategy and Trigger Criteria
We will monitor transient streams (to which several we have direct access)
- if a transient shows a rise or decline of more than 0.2 magnitude per
day, a g-r or g-i color less than 0.3, and is accompanied by the public
report of an X-ray counterpart (e.g. from Swift or Einstein Probe),
we will trigger VLT/X-Shooter to obtain a classification spectrum
(we request 10 x1hr triggers for up to 10 candidates events). If
the spectrum resembles that of the prototypical LFBOT AT2018cow, we
will trigger XMM (followed by CXO and HST). The XMM observing strategy
consists of 10 times 20ks XMM observations (making use of EPIC and OM),
spaced over 10-15 days. This cadence is sufficient to capture the timing
of a break in the lightcurve (with a precision of a few days), and the
total time sufficient to detect any quasi-periodic oscillation at high
significance. The CXO and HST ToOs triggers will be slow/non-disruptive.