TIME-DEPENDENT MODELS OF FLARES FROM SAGITTARIUS A*

2010/05/31 by Katie Dodds-Eden, Prateek Sharma, Eliot Quataert +4
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Flare #Pulsars and Gravitational Waves Research #Sagittarius #Sagittarius A* #Solar flare #Stars #astro-ph.GA #astro-ph.HE

paper · pdf · doi:10.1088/0004-637x/725/1/450

published as The Astrophysical Journal, Volume 725, Issue 1, pp. 450-465 (2010) · 18 pages, 10 figures, ApJ accepted

arxiv created 2010/10/07 · openalex publication_date 2010/11/19 · arxiv updated 2010/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05

Abstract

The emission from Sgr A*, the supermassive black hole in the Galactic Center, shows order of magnitude variability ("flares") a few times a day that is particularly prominent in the near-infrared (NIR) and X-rays. We present a time-dependent model for these flares motivated by the hypothesis that dissipation of magnetic energy powers the flares. We show that episodic magnetic reconnection can occur near the last stable circular orbit in time-dependent magnetohydrodynamic simulations of black hole accretion—the timescales and energetics of these events are broadly consistent with the flares from Sgr A*. Motivated by these results, we present a spatially one-zone time-dependent model for the electron distribution function in flares, including energy loss due to synchrotron cooling and adiabatic expansion. Synchrotron emission from transiently accelerated particles can explain the NIR/X-ray light curves and spectra of a luminous flare observed on 2007 April 4. A significant decrease in the magnetic field strength during the flare (coincident with the electron acceleration) is required to explain the simultaneity and symmetry of the simultaneous light curves. Our models predict that the NIR and X-ray spectral indices are related by Δα ≃ 0.5 (where ν F ν ∝ ν α ) and that there is only modest variation in the spectral index during flares. We also explore implications of this model for longer wavelength (radio-submillimeter) emission seemingly associated with X-ray and NIR flares; we argue that a few hour decrease in the submillimeter emission is a more generic consequence of large-scale magnetic reconnection than delayed radio emission from adiabatic expansion.

Citations

• MHD SIMULATIONS OF ACCRETION ONTO Sgr A*: QUIESCENT FLUCTUATIONS, OUTBURSTS, AND QUASIPERIODICITY
• The First Measurement of Spectral Lines in a Short-Period Star Bound to the Galaxy’s Central Black Hole: A Paradox of Youth
• Flaring Activity of Sagittarius A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma
• SimultaneousChandra, CSO, and VLA Observations of Sgr A*: The Nature of Flaring Activity
• On the Nature of the Variable Infrared Emission from Sagittarius A*
• A powerful local shear instability in weakly magnetized disks. I - Linear analysis. II - Nonlinear evolution
• Faraday Rotation in Global Accretion Disk Simulations: Implications for Sgr A*
• Bremsstrahlung, Synchrotron Radiation, and Compton Scattering of High-Energy Electrons Traversing Dilute Gases
• Polarimetry of near-infrared flares from Sagittarius A*
• Electron Acceleration around the Supermassive Black Hole at the Galactic Center
• Magnetically Driven Accretion Flows in the Kerr Metric. I. Models and Overall Structure
• A time-dependent jet model for the emission from Sagittarius A*
• Nuclear Activity in Nearby Galaxies
• K-band polarimetry of an Sgr A* flare with a clear sub-flare structure
• A polarized infrared flare from Sagittarius A* and the signatures of orbiting plasma hotspots
• The Nature of the 10 kilosecond X-ray flare in Sgr A*
• First simultaneous NIR/X-ray detection of a flare from Sgr A*
• X-ray hiccups from Sagittarius A* observed by XMM-Newton - The second brightest flare and three moderate flares caught in half a day