Abstract for Proposal 092347
Follow-up Observations of New X-ray Transients from the EP-WXT Pathfinder
The study of X-ray transients improves our understanding of the extreme
physical processes in the Universe. The newly launched EP-WXT pathfinder
is a wide-field lobster-eye X-ray telescope in the 0.5-4 keV band, which
can perform sky monitoring in soft X-rays. With improved sensitivity
of (3-4)E-11 erg/(cm2·s), it has the potential to discover new X-ray
transients and variables. Follow-up observations with large X-ray
observatories are essential for source identification, localization,
and characterization. We propose an XMM-Newton ToO program to carry
out follow-up observations for scientifically interesting new X-ray
transients. This program will also provide experiences for future
follow-ups from the EP satellite, which has a much larger FoV of 3600
deg2 and is to be launched in 2023.
Details on Observing Strategy and Trigger Criteria
For every new transient detected by the EP-WXT pathfinder, our
basic strategy is to trigger prompt Swift ToO observations for source
confirmation and multi-wavelength flux measurements. Then based on the
source brightness and properties, we will decide if a deep XMM-Newton
ToO observation should be triggered. Once a new X-ray event potentially
related to a TDE, HV AGN or CL AGN is identified during our data analysis
for the EP-WXT pathfinder, Swift ToO observations will be triggered
within one week to verify the source and monitor its multi-wavelength
flux evolution. The typical timescale of a TDE, an AGN flare, or a
changing-look phenomenon, is from months to years, so a regular reaction
time of a few days is acceptable. If its X-ray flux in 0.3-10 keV is
≳ 1E-12 erg/(cm2·s), an XMM-Newton ToO observation of 40 ks will be
triggered. For other types of newly detected X-ray transients, we will
first exclude their origins of being stellar flares, and then adopt the
same triggering flux to trigger a 40 ks XMM-Newton ToO observation.