The recently discovered extended TeV source HESS J1834-087 is associated with both a diffuse X-ray enhancement and a molecular cloud , projected at the center of an old radio supernova remnant G23.3-0.3 ( SNR W41 ) .
New HI observations from the VLA Galactic Plane Survey ( VGPS ) show unambiguous structures associated with W41 in the radial velocity range of 53 to 63 km/s , so we obtain for W41 a distance of 4 \pm 0.2 kpc .
A new higher sensitivity VGPS continuum image of W41 at 1420 MHz shows faint emission in its eastern part not detected by previous observations , so we provide a new angular size of 36 ^ { \prime } \times 30 ^ { \prime } in b - l direction ( average radius of 19 pc ) .
We estimate for W41 an age of \sim 10 ^ { 5 } yr. A new XMM-Newton observation reveals diffuse X-ray emission within the HESS source and suggests an association between the X-ray and \gamma -ray emission .
The high-resolution ^ { 13 } CO images of W41 further reveal a giant molecular cloud ( GMC ) located at the center of W41 , likely associated with W41 in the the radial velocity range of 61 to 66 km/s .
Altogether , the new observations can be interpreted as providing the first evidence that an old SNR encounters a GMC to emit TeV gamma-rays in the cloud material .