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Supernova enhanced cosmic ray ionization and induced chemistry in a molecular cloud of W51C

Abstract : Cosmic rays pervade the Galaxy and are thought to be accelerated in supernova shocks. The interaction of cosmic rays with dense interstellar matter has two important effects: 1) high energy (>1 GeV) protons produce {\gamma}-rays by {\pi}0-meson decay; 2) low energy (< 1 GeV) cosmic rays (protons and electrons) ionize the gas. We present here new observations towards a molecular cloud close to the W51C supernova remnant and associated with a recently discovered TeV {\gamma}-ray source. Our observations show that the cloud ionization degree is highly enhanced, implying a cosmic ray ionization rate ~ 10-15 s-1, i.e. 100 times larger than the standard value in molecular clouds. This is consistent with the idea that the cloud is irradiated by an enhanced flux of freshly accelerated low-energy cosmic rays. In addition, the observed high cosmic ray ionization rate leads to an instability in the chemistry of the cloud, which keeps the electron fraction high, ~ 10-5, in a large fraction (Av \geq 6mag) of the cloud and low, ~ 10-7, in the interior. The two states have been predicted in the literature as high- and low-ionization phases (HIP and LIP). This is the observational evidence of their simultaneous presence in a cloud.
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http://hal.in2p3.fr/in2p3-00641334
Contributor : Claudine Bombar <>
Submitted on : Tuesday, November 15, 2011 - 2:34:05 PM
Last modification on : Friday, November 27, 2020 - 11:24:20 AM

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C. Ceccarelli, Pierre Hily-Blant, T. Montmerle, G. Dubus, Y. Gallant, et al.. Supernova enhanced cosmic ray ionization and induced chemistry in a molecular cloud of W51C. The Astrophysical journal letters, Bristol : IOP Publishing, 2011, 740, pp.L4. ⟨10.1088/2041-8205/740/1/L4⟩. ⟨in2p3-00641334⟩

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