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High Energy Processes around Black Holes and Jets

Grant number: 24/09383-4
Support Opportunities:Scholarships in Brazil - Post-Doctoral
Effective date (Start): October 01, 2024
Effective date (End): September 30, 2026
Field of knowledge:Physical Sciences and Mathematics - Astronomy - Extragalactic Astrophysics
Principal Investigator:Elisabete Maria de Gouveia Dal Pino
Grantee:Bambhaniya Parthraj
Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Associated research grant:21/02120-0 - Investigation of high energy and plasma astrophysics phenomena, installation of the ASTRI-Mini Array & construction of the Cherenkov Telescope Array Small Size Telescopes (CTA-SSTs), AP.ESP

Abstract

Black holes (BHs) play major roles in astrophysical processes through phenomena like accretion and relativistic jets, acting as cosmic ray accelerators and gamma-ray emitters. They encompass stellar-mass BHs in binaries and supermassive BHs in active galactic nuclei (AGNs), being also crucial for powering gamma-ray bursts (GRBs). Relativistic jets from BHs attain high Lorentz factors, essential for their propagation, with magnetic reconnection facilitating the conversion of magnetic to kinetic energy.Blazars, a subset of AGNs with jets directed towards Earth, are significant extragalactic gamma-ray sources. Challenges arise from TeV gamma-ray flares in blazars like PKS2155-304 and the detection of IceCube neutrinos coinciding with gamma-ray flares in TXS 0506+056. Minute-scale variability in PKS2155-304's TeV emission implies compact, fast acceleration regions, necessitating unusually high Lorentz factors to prevent self-absorption and pair creation. Magnetic reconnection, involving misaligned current sheets within jets, is proposed to explain such variability and compactness. Similarly, in GRBs, magnetic reconnection may explain transitions from magnetically to kinetically dominated flows and prompt gamma-ray emission.Three-dimensional relativistic magnetohydrodynamical (R-MHD) simulations of jets reveal that kink instabilities cause substantial magnetic disruption and turbulence-induced fast magnetic reconnection. This process efficiently converts magnetic energy into kinetic energy, facilitating particle acceleration in AGN, GRB, and binary BH (BHB) jets without requiring strong shocks. Stochastic Fermi-like acceleration in reconnection sites accelerates particles to high energies, generating gamma-rays and neutrinos in compact regions.Understanding the origin of TeV gamma-ray emission in non-blazar sources like low-luminosity AGNs (LLAGNs) poses another challenge. Observations suggest compact emission regions near the cores of sources such as IC 310, M87, Per A, and NGC 1068. An possible scenario suggests particle acceleration via magnetic reconnection in the BH core region. Correlations between gamma-ray luminosity and BH mass for different sources imply distinct particle populations and/or emission locations for blazars/GRBs versus LLAGNs/BHBs.The spectral states of ultra-luminous X-ray sources (ULXs) are another area of ongoing debate. Studies propose ULXs as highly magnetized accreting systems, though this doesn't fully explain observed hard spectral states. Alternatives include neutron stars or horizon-less ultra-compact objects (UCOs) instead of BHs. This research will employ multidimensional numerical modeling to explore BH phenomena, detecting magnetic reconnection events, conducting radiative transfer calculations, simulating particle acceleration, and calculating high-energy emissions. It will apply 2D and 3D R-MHD and general relativistic MHD simulations to study BH accretion disks and jets using tools like HARM and ATHENA++. Enhanced magnetic reconnection-search algorithms with machine learning will improve detection accuracy. Radiative transfer calculations using GRMonty map photon fields, estimating synchrotron and inverse Compton emissions. The project will inject test particles into simulated MHD domains, tracking their acceleration through stochastic processes at reconnection sites using the GACCEL algorithm. Additional mechanisms like curvature drift and shock acceleration are considered. Photon and neutrino flux computations using CRPropa derive spectral energy distributions (SEDs) for VHE emissions and neutrinos. Model validations against observed data from LLAGNs, blazar jets, and potential CTA and ASTRI Mini-Array targets will refine the theoretical predictions. Exploring whether ULXs can be explained by UCOs instead of BHs broadens understanding of high-energy processes, integrating advanced modeling and AI to unveil the universe's energetic mechanisms.

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