* Astronomy

Blobrana · L

RE: SNR W41

Blobrana · L

Title: The Distances of SNR W41 and overlapping HII regions
Authors: Denis A. Leahy, Wenwu Tian

New HI images from the VLA Galactic Plane Survey show prominent absorption features associated with the supernovae remnant G23.3-0.3 (SNR W41). We highlight the HI absorption spectra and the ^{13}CO emission spectra of eight small regions on the face of W41, including four HII regions, three non-thermal emission regions and one unclassified region. The maximum velocity of absorption for W41 is 78 ±2 km/s and the CO cloud at radial velocity 95±5 km/s is behind W41. Because an extended TeV source, a diffuse X-ray enhancement and a large molecular cloud at radial velocity 77 ±5 km/s are also projected at the centre of W41, these yield the kinematic distance of 3.9 to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21 and G23.07+0.25 are at the far kinematic distances (~9.9 kpc and ~ 10.6 kpc respectively) of their recombination-line velocities (103 ±0.5 km/s and 89.6 ±2.1 km/s respectively), G23.07-0.37 is at the near kinematic distance (4.4 ±0.3 kpc) of its recombination-line velocity (82.7 ±2.0 km/s), and G23.27-0.27 is probably at the near kinematic distance (4.1 ±0.3 kpc) of its recombination-line velocity (76.1 ±0.6 km/s).

Read more (611kb, PDF)

Blobrana · L

Title: VLA and XMM-Newton observations of the SNR W41/TeV Gamma-ray source HESS J1834-087
Authors: W.W. Tian, Z. Li, D.A. Leahy, Q.D. Wang
(revised v2)

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 ±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 give a new angular size of 36'x30' in b-l direction (average radius of 19 pc). We estimate for W41 a Sedov age of ~10e5 yr. 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 centre 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.

Read more (332kb, PDF)