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arXiv 1010.3252astro-ph.HE
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通过H3 +观测研究超新星遗迹IC 443附近的Cosmic-Ray电离率

Investigating the Cosmic-Ray Ionization Rate Near the Supernova Remnant IC 443 Through H3+ Observations

Nick Indriolo, Geoffrey A. Blake, Miwa Goto, Tomonori Usuda, Takeshi Oka, T. R. Geballe, Brian D. Fields, Benjamin J. McCall

摘要:

观测和理论证据表明,高能银河系宇宙射线主要是由超新星遗迹加速的。如果低能宇宙射线也是如此,超新星遗迹附近的电离率应该高于一般银河系星际介质(ISM)。为了推断该地区的宇宙射线电离率,我们在6条穿过IC 443附近分子物质的视线中寻找了H3+的吸收特征。IC 443是一个研究得很好的超新星遗迹与周围分子物质相互作用的案例。在其中两条视线中(朝向ALS 8828和HD 254577),我们发现了较大的H3+柱密度,N(H3+)约为3* 10 ^-14 cm^-2,并推断出zeta 2的电离率约为2*10^-15 s^-1,比平均扩散分子云视线中的电离率大5倍。然而,其他4条视线的3 σ上限与典型的银河值一致。这种大范围的电离率可能是粒子加速和传播效应的结果,这预示着宇宙射线光谱和电离率应该在残骸内部和周围发生变化。虽然我们无法确定H3+的吸收是发生在冲击后(内部)还是冲击前(外部)的气体中,但推断出的大电离率表明IC 443实际上正在加速大量低能宇宙射线。然而,目前还不清楚这群人是否能传播到ISM足够远的地方,以解释弥漫的银河视线中推断的电离率。

英文摘要:

Observational and theoretical evidence suggests that high-energy Galactic cosmic rays are primarily accelerated by supernova remnants. If also true for low-energy cosmic rays, the ionization rate near a supernova remnant should be higher than in the general Galactic interstellar medium (ISM). We have searched for H3+ absorption features in 6 sight lines which pass through molecular material near IC 443---a well-studied case of a supernova remnant interacting with its surrounding molecular material---for the purpose of inferring the cosmic-ray ionization rate in the region. In 2 of the sight lines (toward ALS 8828 and HD 254577) we find large H3+ column densities, N(H3+)~3*10^14 cm^-2, and deduce ionization rates of zeta_2~2*10^-15 s^-1, about 5 times larger than inferred toward average diffuse molecular cloud sight lines. However, the 3 sigma upper limits found for the other 4 sight lines are consistent with typical Galactic values. This wide range of ionization rates is likely the result of particle acceleration and propagation effects, which predict that the cosmic-ray spectrum and thus ionization rate should vary in and around the remnant. While we cannot determine if the H3+ absorption arises in post-shock (interior) or pre-shock (exterior) gas, the large inferred ionization rates suggest that IC 443 is in fact accelerating a large population of low-energy cosmic rays. Still, it is unclear whether this population can propagate far enough into the ISM to account for the ionization rate inferred in diffuse Galactic sight lines.

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