Fast variability and millimeter/IR flares in grmhd models of sgr a∗ from strong-field gravitational lensing

Chi Kwan Chan, Dimitrios Psaltis, Feryal �zel, Lia Medeiros, Daniel Marrone, Aleksander Sadowski, Ramesh Narayan

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


We explore the variability properties of long, high-cadence general relativistic magnetohydrodynamic (GRMHD) simulations across the electromagnetic spectrum using an efficient, GPU-based radiative transfer algorithm. We focus on both standard and normal evolution (SANE) and magnetically arrested disk (MAD) simulations with parameters that successfully reproduce the time-averaged spectral properties of Sgr A∗ and the size of its image at 1.3 mm. We find that the SANE models produce short-timescale variability with amplitudes and power spectra that closely resemble those inferred observationally. In contrast, MAD models generate only slow variability at lower flux levels. Neither set of models shows any X-ray flares, which most likely indicates that additional physics, such as particle acceleration mechanisms, need to be incorporated into the GRMHD simulations to account for them. The SANE models show strong, short-lived millimeter/infrared (IR) flares, with short (≲1 hr) time lags between the millimeter and IR wavelengths, that arise from the combination of short-lived magnetic flux tubes and strong-field gravitational lensing near the horizon. Such events provide a natural explanation for the observed IR flares with no X-ray counterparts.

Original languageEnglish (US)
Article number103
JournalAstrophysical Journal
Issue number2
StatePublished - Oct 20 2015


  • Galaxy: center
  • accretion, accretion disks
  • black hole physics
  • radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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