Following up the afterglow:strategy for X-ray observation triggered by gravitational wave events

The multi-messenger observation of coalescing compact binary systems promises great scientific treasure.However,synthesising observations from both gravitational wave and electromagnetic channels remains challenging.In the context of the day-to-week long emission from a macronova,the binary neutron star merger GW170817 remains the only event with successful electromagnetic followup.In this manuscript,we explore the possibility of using the early stage X-ray afterglow to search for the electromagnetic counterpart of a gravitational wave event.Two algorithms,the simple and straightforward sequential observation(SO)and the step-wise optimizing local optimization are considered and applied to some simulated events.We consider the WXT from the proposed Einstein Probe as a candidate X-ray telescope,which has a very wide field of view of 3600 deg^(2).Benefiting from the large field of view and high sensitivity,we find that the SO algorithm not only is easy to implement,but also promises a good chance of actual detection.