Recent advances in numerical simulations of magnetically arrested accretion onto supermassive black holes have shed light on the formation and dynamics of magnetospheric current sheets near the black hole horizon. By considering the pair magnetization σ _e in the upstream region and the mass accretion rate ṁ (in units of the Eddington mass accretion rate) as free parameters we estimate the strength of the magnetic field and develop analytical models, motivated by recent three-dimensional particle-in-cell simulations, to describe the populations of relativistic electrons and positrons (pairs) in the reconnection region. Applying our model to M87*, we numerically compute the non-thermal photon spectra for various values of σ _e . We show that pairs that are accelerated up to the synchrotron radiation-limited energy while meandering across both sides of the current sheet, can produce MeV flares with luminosity of ∼ 10⁴¹ erg s^-1 — independent of σ _e — for a black hole accreting at ṁ=10^-5. Pairs that are trapped in the transient current sheet can produce X-ray counterparts to the MeV flares, lasting about a day for current sheets with length of a few gravitational radii. We also show that the upstream plasma can be enriched due to photon-photon pair creation, and derive a new equilibrium magnetization of σ _e ∼ 10³-10⁴ for ṁ = 10^-6 - 10^-5. Additionally, we explore the potential of magnetospheric current sheets to accelerate protons to ultra-high energies, finding that while acceleration to such energies is limited by various loss mechanisms, such as synchrotron and photopion losses from the non-thermal emission from pairs, maximal proton energies in the range of a few EeV are attainable in magnetospheric sheets forming around supermassive sub-Eddington accreting black holes.

中文翻译：

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磁层电流片在 M87* 中对富集和超高能质子加速中的作用


超大质量黑洞上磁阻吸积的数值模拟的最新进展揭示了黑洞视界附近磁层电流片的形成和动力学。通过将上游区域的对磁化σ _e 和质量吸积率 ṁ（以 Eddington 质量吸积率为单位）视为自由参数，我们估计了磁场的强度，并开发了分析模型，受最近的三维胞内粒子模拟的启发，以描述相对论电子和正电子（对）的群在重连接区域中。将我们的模型应用于 M87*，我们数值计算了 σ _e 的各种值的非热光子光谱。我们表明，在电流片的两侧蜿蜒时加速到同步辐射限制能量的对可以产生光度为 ∼ 10⁴¹ erg ^s-1 的 MeV 耀斑——与σ _e 无关——对于在 ṁ=^10-5 处吸积的黑洞。被困在瞬态洋流片中的对可以产生与 MeV 耀斑对应的 X 射线，对于长度为几个引力半径的洋流片，持续大约一天。我们还表明，由于光子-光子对的产生，上游等离子体可以被富集，并得出 ṁ = ^10-6 - ^10-5 时 σ _e ∼^{10 3-10 4} 的新平衡磁化强度。 此外，我们探索了磁层电流片将质子加速到超高能量的潜力，发现虽然对此类能量的加速受到各种损耗机制的限制，例如同步加速器和光子损耗来自成对的非热发射，但在超大质量亚爱丁顿吸积黑洞周围形成的磁层片中可以获得几个 EeV 范围内的最大质子能量。