Time-dependent models of flares from sagittarius a

Katie Dodds-Eden, Prateek Sharma, Eliot Quataert, Reinhard Genzel, Stefan Gillessen, Frank Eisenhauer, Delphine Porquet

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

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 timedependent 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 timedependent 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 νF ν ∝ να) 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.

Original languageEnglish (US)
Pages (from-to)450-465
Number of pages16
JournalAstrophysical Journal
Volume725
Issue number1
DOIs
StatePublished - Dec 10 2010

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Accretion
  • Accretion disks
  • Black hole physics
  • Galaxy: center
  • Infrared: general
  • Radiation mechanisms: general

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