High-energy radiation from remnants of neutron star binary mergers

We study high-energy emission from the mergers of neutron star binaries as electromagnetic counterparts to gravitational waves aside from short gamma-ray bursts. The mergers entail significant mass ejection, which interacts with the surrounding medium to produce similar but brighter remnants than supernova remnants in a few years. We show that electrons accelerated in the remnants can produce synchrotron radiation in x rays detectable at similar to 100 Mpc by current generation telescopes and inverse Compton emission in gamma rays detectable by the Fermi Large Area Telescopes and the Cherenkov Telescope Array under favorable conditions. Optical synchrotron radiation is also detectable by telescopes with good angular resolution. The remnants may have already appeared in high-energy surveys such as the Monitor of All-sky X-ray Image and the Fermi Large Area Telescope as unidentified sources. We also suggest that the merger remnants could be the origin of ultrahigh-energy cosmic rays beyond the knee energy, similar to 10(15) eV, in the cosmic ray spectrum.