Fallback Accretion Model for the Years-to-Decades X-ray Counterpart to GW170817

Understand

A new component was reported in the X-ray counterpart to the binary neutron-star merger and gravitational wave event GW170817, exceeding the afterglow emission from an off-axis structured jet.

• The afterglow emission from the kilonova/macronova ejecta may explain the X-ray excess but exceeds the radio observations if the spectrum is the same.
• We propose a fallback accretion model that a part of ejecta from the neutron star merger falls back and forms a disk around the central compact object.
• In the super-Eddington accretion phase, the X-ray luminosity stays near the Eddington limit of a few solar masses and the radio is weak, as observed.