Sgr A* X-ray flares from non-thermal particle acceleration in a magnetically arrested disc

Abstract

Sgr A* exhibits flares in the near-infrared and X-ray bands, with the luminosity in these bands increasing by factors of $10-100$ for $\approx 60$ minutes. One of the models proposed to explain these flares is synchrotron emission of non-thermal particles accelerated by magnetic reconnection events in the accretion flow. We use the results from PIC simulations of magnetic reconnection to post-process 3D two-temperature GRMHD simulations of a magnetically arrested disc (MAD). We identify current sheets, retrieve their properties, estimate their potential to accelerate non-thermal particles and compute the expected non-thermal synchrotron emission. We find that the flux eruptions of MADs can provide suitable conditions for accelerating non-thermal particles to energies ${\gamma }_e\lesssim 10^6$ and producing simultaneous X-ray and near-infrared flares. For a suitable choice of current-sheet parameters and a simpified synchrotron cooling prescription, the model can simultaneously reproduce the quiescent and flaring X-ray luminosities as well as the X-ray spectral shape. While the near-infrared flares are mainly due to an increase in the temperature near the black hole during the MAD flux eruptions, the X-ray emission comes from narrow current sheets bordering highly magnetized, low-density regions near the black hole and equatorial current sheets where the flux on the black hole reconnects. As a result, not all infrared flares are accompanied by X-ray ones. The non-thermal flaring emission can extend to very hard ($\lesssim 100$ keV) X-ray energies.

12 pages, 8 Figures, Accepted for publication in MNRAS

References in corpus (17)

• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• An Update on Monitoring Stellar Orbits in the Galactic Center
• Formation of Hard Power-laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection
• Black hole flares: ejection of accreted magnetic flux through 3D plasmoid-mediated reconnection
• The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
• Magnetically Arrested Disks and Origin of Poynting Jets: Numerical Study
• Polarimetry of near-infrared flares from Sagittarius A*
• The Disc-Jet Symbiosis Emerges: Modeling the Emission of Sagittarius A* with Electron Thermodynamics
• The Power of Imaging: Constraining the Plasma Properties of GRMHD Simulations using EHT Observations of Sgr A*
• Plasma diagnostic potential of 2p4f in N${}^{+}$ -- accurate wavelengths and oscillator strengths
• Electron and proton heating in trans-relativistic magnetic reconnection
• Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity
• Sgr A* near-infrared flares from reconnection events in a magnetically arrested disc
• The Radiative Efficiency and Spectra of Slowly Accreting Black Holes from Two-Temperature GRRMHD Simulations
• Dynamically important magnetic fields near the event horizon of Sgr A*
• The X-ray Flux Distribution of Sagittarius A* as Seen by Chandra
• The Flux Distribution of Sgr A*

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• Spinning black holes magnetically connected to a Keplerian disk -- Magnetosphere, reconnection sheet, particle acceleration and coronal heating
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• Effective resistivity in relativistic collisionless plasmoid-mediated reconnection
• Synchrotron Pair Production Equilibrium in Relativistic Magnetic Reconnection
• Probing Plasma Physics with Spectral Index Maps of Accreting Black Holes on Event Horizon Scales
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