A cut-off in the TeV gamma-ray spectrum of the SNR Cassiopeia A
A cut-off in the TeV gamma-ray spectrum of the SNR Cassiopeia A
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DOI：
10.1093/mnras/stx2079
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发表时间：
2017-07
影响因子：
4.8
通讯作者：
M. L. Ahnen;S. Ansoldi;L. A. Antonelli;C. Arcaro;A. Babi'c;B. Banerjee;P. Bangale;U. D. Almeida
中科院分区：
文献类型：
--
作者：
M. L. Ahnen;S. Ansoldi;L. A. Antonelli;C. Arcaro;A. Babi'c;B. Banerjee;P. Bangale;U. D. Almeida
人们普遍认为，大部分银河系宇宙射线在超新星遗迹（SNRs）中被加速。然而，没有观测证据的PeV能量的粒子在SNR的存在尚未found.The年轻的历史SNR仙后座A（Cas A）出现作为一个最好的候选人来研究加速过程。在2014年12月至2016年10月期间，我们用MAGIC望远镜观测了Cas A，积累了158小时的高质量数据。我们导出了100 GeV到10 TeV的源的光谱。我们还分析了2008年的费米LAT，以获得60 MeV和500 GeV之间的光谱形状。LAT和MAGIC望远镜测量的光谱在误差范围内是相容的，并且在最高能量处显示出明显的关闭（4.6 σ），这可以用指数截止值Ec = 3.5（λ max，λ max，λ max）_（stat）（λ max，λ max，λ max）_（sys）TeV来描述。从60 MeV到10 TeV的伽马射线发射可以归因于光谱指数为2.2的高能质子群，能量截止为2.10 TeV。这一结果表明，目前Cas A对高能（100PeV）宇宙射线海的贡献并不显著。单带轻子模型不能自己再现多波长光谱能量分布。此外，如果MAGIC观测到的通量中有不可忽略的一部分是由轻子产生的，那么辐射应该是在一个低磁场（B<100µG）的区域发射的，就像在反向激波中一样。
It is widely believed that the bulk of the Galactic cosmic rays are accelerated in supernova remnants (SNRs). However, no observational evidence of the presence of particles of PeV energies in SNRs has yet been found. The young historical SNR Cassiopeia A (Cas A) appears as one of the best candidates to study acceleration processes. Between December 2014 and October 2016 we observed Cas A with the MAGIC telescopes, accumulating 158 hours of good-quality data. We derived the spectrum of the source from 100 GeV to 10 TeV. We also analysed ∼8 years of F ermiLAT to obtain the spectral shape between 60 MeV and 500 GeV. The spectra measured by the LAT and MAGIC telescopes are compatible within the errors and show a clear turn off (4.6 σ) at the highest energies, which can be described with an exponential cut-off at Ec = 3.5(₋₁‚₀⁺¹’⁶ )_(stat) (⁺⁰’⁸ ₋‚₀₉)_(sys) TeV. The gamma-ray emission from 60 MeV to 10 TeV can be attributed to a population of high-energy protons with spectral index ∼2.2 and energy cut-off at ∼10 TeV. This result indicates that Cas A is not contributing to the high energy (∼PeV) cosmic-ray sea in a significant manner at the present moment. A one-zone leptonic model fails to reproduce by itself the multiwavelength spectral energy distribution. Besides, if a non-negligible fraction of the flux seen by MAGIC is produced by leptons, the radiation should be emitted in a region with a low magnetic field (B<≈100µG) like in the reverse shock.