Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
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DOI：
10.1126/science.1231160
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发表时间：
2013-02-15
期刊：
影响因子：
56.9
通讯作者：
Zimmer, S.
中科院分区：
文献类型：
--
作者：
Ackermann, M.;Ajello, M.;Zimmer, S.
宇宙射线是加速到相对论速度的粒子（主要是质子）。尽管超新星遗迹（SNRs）是银河系宇宙射线的来源这一观点得到了广泛的认同，但仍然缺乏这些天体中质子加速的明确证据。当加速的质子遇到星际物质时，它们会产生中性的π介子，后者又会衰变成伽马射线。这为探测质子的加速点提供了一种令人信服的方法。π介子衰变伽马射线的识别一直很困难，因为高能电子也通过韧致辐射和逆康普顿散射产生伽马射线。我们用费米大天区望远镜探测到了两个信噪比IC 443和W 44的γ射线谱中的特征π介子衰变特征。这一探测提供了宇宙射线质子在SNR中加速的直接证据。
Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs.