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 \pm 0.1 and 1.6 \pm 0.2 , respectively .
The photon indices as well as the flux ratio of F _ { \mathrm { nebula } } / F _ { \mathrm { pointlike } } \sim 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 2.1 \times 10 ^ { 31 } ( d /540 pc ) ^ { 2 } ergs s ^ { -1 } , where d is the distance to the Loop .
This implies a spin-down loss-energy \dot { E } \sim 2.6 \times 10 ^ { 35 } ( d /540 pc ) ^ { 2 } ergs s ^ { -1 } .
The location of the neutron star candidate , \sim 2 ^ { \circ } away from the geometric center of the Loop , implies a high transverse velocity of \sim 1850 ( \theta /2 ^ { \circ } ) ( d /540 pc ) ( t /10 kyr ) ^ { -1 } km s ^ { -1 } , assuming the currently accepted age of the Cygnus Loop .