Suzaku observed the region including HESS J1809 - 193 , one of the TeV unidentified ( unID ) sources , and confirmed existence of the extended hard X-ray emission previously reported by ASCA , as well as hard X-ray emission from the pulsar PSR J1809 - 1917 in the region .
One-dimensional profile of the diffuse emission is represented with a Gaussian model with the best-fit \sigma of 7 \pm 1 arcmin .
The diffuse emission extends for at least 21 pc ( at the 3 \sigma level , assuming the distance of 3.5 kpc ) , and has a hard spectrum with the photon index of \Gamma \sim 1.7 .
The hard spectrum suggests the pulsar wind nebula ( PWN ) origin , which is also strengthened by the hard X-ray emission from PSR J1809 - 1917 itself .
Thanks to the low background of Suzaku XIS , we were able to investigate spatial variation of the energy spectrum , but no systematic spectral change in the extended emission is found .
These results imply that the X-ray emitting pulasr wind electrons can travel up to 21 pc from the pulsar without noticable energy loss via synchrotron emission .