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Title:
Radio and X-ray images of the SNR G18.8+0.3 interacting with molecular clouds
Authors:
Tian, W. W.; Leahy, D. A.; Wang, Q. D.
Affiliation:
AA(National Astronomical Observatoires, CAS, Beijing 100012, PR China ; Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada ), AB(Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada), AC(Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA)
Publication:
Astronomy and Astrophysics, Volume 474, Issue 2, November I 2007, pp.541-547 (A&A Homepage)
Publication Date:
11/2007
Origin:
EDP Sciences
Astronomy Keywords:
ISM: supernova remnants, galaxies: ISM, galaxies: kinematics and dynamics, ISM: structure
DOI:
10.1051/0004-6361:20077527
Bibliographic Code:
2007A&A...474..541T

Abstract

New HI images from the VLA Galactic Plane Survey (VGPS) show clear absorption features associated with the supernova remnant (SNR) G18.8+0.3. High-resolution 13CO images reveal that molecular clouds overlap the radio filaments of G18.8+0.3. The 13CO emission spectrum over the full velocity range in the direction of G18.8+0.3 shows two molecular components with high brightness-temperature and three molecular components with low brightness-temperature, all with respective HI absorption. This implies that these clouds are in front of G18.8+0.3. In the HI images, the highest velocity absorption feature seen against the continuum image of G18.8+0.3 is at 129 km s-1, which corresponds to the tangent point in this direction. This yields a lower distance limit of 6.9 kpc for G18.8+0.3. Absence of absorption at negative velocities gives an upper distance limit of 15 kpc. The broadened profile at 20±5 km s-1 in the 13CO emission spectra is a strong indicator of a possible SNR/CO cloud interaction. Thus, G18.8+0.3 is likely to be at the distance of about 12 kpc. The upper mass limit and mean density of the giant CO cloud at 20± 5 km s-1 are ~6 × 105 Msun and ~2× 102 cm-3. We find an atomic hydrogen column density in front of G18.8+0.3 of N_HI ˜ 2×1022 cm-2. The ROSAT PSPC observations show a diffuse X-ray enhancement apparently associated with part of the radio shell of G18.8+0.3. Assuming an association, the unabsorbed flux is 2.2× 10-12 erg cm-2 s-1, suggesting an intrinsic luminosity of 3.6× 1034 erg s-1 for G18.8+0.3.
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