2012ApJ...754L...7K

We report on a discovery of a diffuse nebula containing a pointlike source in the southern blowout region of the Cygnus Loop supernova remnant, based on Suzaku and XMM-Newton observations. The X-ray spectra from the nebula and the pointlike source are well represented by an absorbed power-law model with photon indices of 2.2±0.1 and 1.6±0.2, respectively. The photon indices as well as the flux ratio of F_nebula/F_pointlike∼ 4 lead us to propose that the system is a pulsar wind nebula, although pulsations have not yet been detected. If we attribute its origin to the Cygnus Loop supernova, then the 0.5-8 keV luminosity of the nebula is computed to be 2.1x10³¹ (d/540 pc)² erg/s, where d is the distance to the Loop. This implies a spin-down loss-energy {dot}E ∼ 2.6x10³⁵ (d/540 pc)² erg/s. The location of the neutron star candidate, ∼2° away from the geometric center of the Loop, implies a high transverse velocity of ∼1850 (θ/2°) (d/540 pc) (t/10 kyr)^–1 km/s, assuming the currently accepted age of the Cygnus Loop.