Radiation from the impact of broad-line region clouds onto AGN accretion disks

Abstract

Active galactic nuclei are supermassive black holes surrounded by an accretion disk, two populations of clouds, bipolar jets, and a dusty torus. The clouds move in Keplerian orbits at high velocities. In particular, the broad-line region (BLR) clouds have velocities ranging from $1000$ to $10000$ km s${}^{-1}$. Given the extreme proximity of these clouds to the supermassive black hole, frequent collisions with the accretion disk should occur. The impact of BLR clouds onto the accretion disk can produce strong shock waves where particles might be accelerated. The goal of this work is to investigate the production of relativistic particles, and the associated non-thermal radiation in these events. In particular, we apply the model we develop to the Seyfert galaxy NGC 1068. We analyze the efficiency of diffusive shock acceleration in the shock of colliding clouds of the BLR with the accretion disk. We calculate the spectral energy distribution of photons generated by the relativistic particles and estimate the number of simultaneous impacts needed to explain the gamma radiation observed by the Fermi satellite in Seyfert galaxies. We find that is possible to understand the measured gamma emission in terms of the interaction of clouds with the disk if the hard X-ray emission of the source is at least obscured between $20\%$ and $40\%$. The total number of clouds contained in the BLR region might be between $3\times 10^8$ and $6\times 10^8$, which are values in good agreement with the observational evidence. The maximum energy achieved by the protons ($\sim$ PeV) in this context allows the production of neutrinos in the observing range of IceCube.

9 pages, 8 figures, 6 tables. Accepted for publication in A&A

References in corpus (9)

• Time-integrated Neutrino Source Searches with 10 years of IceCube Data
• A massive binary black-hole system in OJ287 and a test of general relativity
• The Magnetohydrodynamics of Shock-Cloud Interaction in Three Dimensions
• Magnetar-energized supernova explosions and GRB-jets
• Galactic outflow driven by the active nucleus and the origin of the gamma-ray emission in NGC 1068
• Gamma-ray opacity of the anisotropic stratified broad-line regions in blazars
• Unveiling the origin of the gamma-ray emission in NGC 1068 with the Cherenkov Telescope Array
• Gamma rays from jets interacting with BLR clouds in blazars
• Numerical simulation of small perturbation on an accretion disk due to the collision of a star with the disk near the black hole

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• Broad-line Region Clouds orbiting an AGN sample
• Electromagnetic signatures of black hole clusters in the center of super-Eddington galaxies
• Modeling the Reverberation Response of the Broad Line Region in Active Galactic Nuclei II: Incorporating Photoionization Models
• Proton Acceleration by Collisionless Shocks in Supermassive Black Hole Coronae: Implications for High-Energy Neutrinos
• Metallicity Ceiling in Quasars from Recycled Stellar Winds
• Super-Accreting Active Galactic Nuclei as Neutrino Sources
• Resonant W and Z Boson Production in FSRQ Jets: Implications for Diffuse Neutrino Fluxes
• Non-thermal emission from fall-back clouds in the Broad-Line Region of Active Galactic Nuclei