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arXiv 2205.09565astro-ph.HE
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射电星系中磁阻星系的高能γ射线

High-energy Gamma-rays from Magnetically Arrested Disks in Nearby Radio Galaxies

Riku Kuze, Shigeo S. Kimura, Kenji Toma

摘要:

来自附近射电星系的GeV伽马射线的起源是未知的。提出了中心黑洞(BH)周围磁制动盘(MAD)的强子发射作为一种可能的情况。粒子在MAD中通过磁重联和随机湍流加速而被加速。我们从Fermi 4LAC-DR 2星表中挑选出15个GeV波段最亮的射电星系,并应用MAD模型。我们发现,当吸积率小于爱丁顿吸积率的0.1%时,我们可以用MAD模型解释GeV波段的数据。在较高的吸积速率下,由于大量低能光子的存在,GeV的γ射线被双光子相互作用吸收。如果我们假设另一个由磁重联给出的电子加热速率的公式,MAD模型就不能再现我们大多数样本的GeV数据。这表明电子加热速率是至关重要的。我们还将MAD模型应用于Sgr A*,发现在银河系中心观测到的GeV γ射线不是来自Sgr A* 的MAD。我们从Sgr A* 估计宇宙射线强度,但它太低,无法解释地球上的高能宇宙射线强度。

英文摘要:

The origins of the GeV gamma-rays from nearby radio galaxies are unknown. Hadronic emission from magnetically arrested disks (MADs) around central black holes (BHs) is proposed as a possible scenario. Particles are accelerated in the MAD by magnetic reconnection and stochastic turbulence acceleration. We pick out the fifteen brightest radio galaxies in the GeV band from the Fermi 4LAC-DR2 catalog and apply the MAD model. We find that we can explain the data in the GeV bands by the MAD model if the accretion rate is lower than 0.1% of the Eddington rate. For a higher accretion rate, GeV gamma-rays are absorbed by two-photon interaction due to copious low-energy photons. If we assume another proposed prescription of the electron heating rate by magnetic reconnection, the MAD model fails to reproduce the GeV data for the majority of our sample. This indicates that the electron heating rate is crucial. We also apply the MAD model to Sgr A* and find that GeV gamma-rays observed at the Galactic center do not come from the MAD of Sgr A*. We estimate the cosmic ray intensity from Sgr A*, but it is too low to explain the high-energy cosmic ray intensity on Earth.

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