X-ray-powered macronovae

Understand

A macronova (or kilonova) was observed as an infrared excess several days after short gamma-ray burst, GRB 130603B.

• Although the $r$-process radioactivity is widely discussed as an energy source, it requires huge mass of ejecta from a neutron star (NS) binary merger.
• We propose a new model that the X-ray excess gives rise to the simultaneously observed infrared excess via thermal re-emission and explore what constraints this would place on the mass and velocity of the ejecta.
• This X-ray-powered model explains both the X-ray and infrared excesses with a single energy source by the central engine like a black hole, and allows for broader parameter region, in particular smaller ejecta mass $\sim10^{-3}-10^{-2}M_{\odot}$ with iron mixed as suggested by general relativistic simulations for typical NS-NS mergers, than the previous models.