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 $σ_{\rm e}$ in the upstream region and the mass accretion rate $\dot{m}$ (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 electron 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 $\sim 10^{41}$~erg s$^{-1}$ -- independent of $σ_e$ -- for a black hole accreting at $\dot{m}=10^{-5}$. 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 $σ_e \sim 10^3-10^4$ for $\dot{m}=10^{-6} - 10^{-5}$. 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.
Diffuse neutrino flux from coronal magnetospheric current sheets of accreting black holes
National and Kapodistrian University of Athens（雅典国立卡波迪斯特里安大学）；Institute of Accelerating Systems and Applications（加速系统与应用研究所）；Columbia University（哥伦比亚大学）；Flatiron Institute（平顿研究所）
Gamma-Ray Millisecond Pulsars: Off-pulse Emission Characteristics, Phase-Resolved Pseudo-Luminosity--Cutoff Energy Correlation, and High-energy Pulsed Emission
Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台暗物质与空间天文重点实验室）；School of Astronomy and Space Science, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）
High-energy radiation from the pulsar Equatorial Current Sheet
Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg（斯特拉斯堡大学）；Research Center for Astronomy and Applied Mathematics, Academy of Athens（雅典科学院天文与应用数学研究中心）
On the universality of the split monopole black hole magnetosphere
Columbia University（哥伦比亚大学）；Anton Pannekoek Institute（安东·潘内克研究所）；Canadian Institute for Theoretical Astrophysics（加拿大理论天体物理研究所）；University of Toronto（多伦多大学）；Perimeter Institute for Theoretical Physics（基础理论物理研究所）；Flatiron Institute（平顿研究所）
Neutrino and pair creation in reconnection-powered coronae of accreting black holes
National and Kapodistrian University of Athens（雅典国立卡波迪斯特里安大学）；Institute of Accelerating Systems & Applications（加速系统与应用研究所）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器中心）；Columbia University（哥伦比亚大学）；Center for Computational Astrophysics, Flatiron Institute（纽约大学柯朗数学科学研究所计算天体物理中心）
