Abstract for Proposal 094424
Testing the Supermassive Black Hole Binary scenario on an eROSITA-selected AGN
Using eROSITA and NICER data, we discovered our most promising
supermassive black hole binary (SMBHB) candidate based on an X-ray
periodic-like light curve with a tentative period of 120 days. We
propose a 190 ks ToO XMM-Newton observation to detect the double-peaked
Fe K-alpha lines, prove their energy shift as they blend and separate
with the phase of the orbit, and thus confirm the binary nature of the
source. We will complement our observation with a pre-approved 120 ks
XMM-Newton ToO observation. With ongoing X-ray monitoring to accurately
determine the period of the signal plus detecting and proving the shift in
the energy of the double Fe K-alpha lines, this project has the potential
to discover the closest-separation SMBHB ever at ~1 milli-pc.
Details on Observing Strategy and Trigger Criteria
The precise moment of the triggering will be defined once the NICER and
Swift X-ray monitoring provide the exact period of the light curve. We
already requested NICER and Swift X-ray monitoring programs. In case
they are not approved, we will request DDT observations to populate the
X-ray light curve and determine the period. Once the period is properly
defined, we will be able to predict the phase and the exact moment of
the 90-degree shift on the orbital motion with respect to the first
120 ks ToO observation. Thus, XMM-Newton will have more than 30 days to
schedule our ToO observation. We will only trigger if i) the NICER and
Swift X-ray monitoring confirm and constrain the periodic variability
and ii) our source can still be covered by the XMM-Newton visibility
window for at least 15 days during the 90-degree shift from the orbital
phase when the first 120 ks ToO observation occurred.