Abstract for Proposal 096133

XMM-Newton follow-up of electromagnetic counterparts to GW triggers during LVKC-

The joint detection of GWs and light from the neutron star (NS) merger GW170817 ushered us into a new era. Deep X-ray observations of GW170817 constrained the structural properties of a relativistic outflow launched by an NS merger for the first time. After these landmark discoveries, the frontier is now to map the X-ray properties of a population of sources. We propose to exploit the unique capabilities of XMM-Newton to constrain the broad-band properties of very nearby NS-bearing mergers, selected from LVKC-O4 GW triggers or electromagnetically identified kilonovae. Our immediate goals are: (i) map the diversity of emission from NS mergers, (ii) test the nature of the remnant object, (iii) determine if all mergers launch a jet, and (iv) enable the first X-ray detections of NS-BH mergers.

Details on Observing Strategy and Trigger Criteria
The observing trigger can come from a variety of instruments at different wavelengths: - high energy instruments with a relatively good positional accuracy of a few armin2 (Swift/BAT, INTEGRAL, Fermi/LAT, MAXI, AGILE); - soft X-ray instruments like Swift/XRT; - optical/NIR counterpart from wide-field surveys and/or targeted searches (only if a firm candidate is available). Reaction time is as fast as possible for the first activation. EPIC in full-frame thin filter. OM in fast timing with u filter. For later observations, the trigger can come from any well-identified GW-EM counterpart.