Ammonia excitation imaging of shocked gas towards the W28 gamma-ray source HESS J1801-233

• Published in: arXiv.org 2016-07
• Main Authors: Maxted, Nigel I, de Wilt, Phoebe, Rowell, Gavin P, Nicholas, Brent P, Burton, Michael G, Walsh, Andrew, Fukui, Yasuo, Kawamura, Akiko
• Format: Article
• Language: English
• Subjects: Ammonia; Disruption; Gamma rays; Line spectra; Molecular clouds; Molecular gases; Sublimation; Supernova remnants
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1607.03061

We present 12 mm Mopra observations of the dense (>10^3 cm^-3 ) molecular gas towards the north-east (NE) of the W28 supernova remnant (SNR). This cloud is spatially well-matched to the TeV gamma-ray source HESS J1801-233 and is known to be a SNR-molecular cloud interaction region. Shock-disruption is evident from broad NH3 (1,1) spectral line-widths in regions towards the W28 SNR, while strong detections of spatially-extended NH3(3,3), NH3(4,4) and NH3(6,6) inversion emission towards the cloud strengthen the case for the existence of high temperatures within the cloud. Velocity dispersion measurements and NH3(n,n)/(1,1) ratio maps, where n=2, 3, 4 and 6, indicate that the source of disruption is from the side of the cloud nearest to the W28 SNR, suggesting that it is the source of cloud-disruption. Towards part of the cloud, the ratio of ortho to para-NH3 is observed to exceed 2, suggesting gas-phase NH3 enrichment due to NH3 liberation from dust grain mantles. The measured NH3 abundance with respect to H2 is ~(1.2+/-0.5)*10^-9, which is not high, as might be expected for a hot, dense molecular cloud enriched by sublimated grain-surface molecules. The results are suggestive of NH3 sublimation and destruction in this molecular cloud, which is likely to be interacting with the W28 SNR shock.