TY - JOUR
T1 - Fast variability and millimeter/IR flares in grmhd models of sgr a∗ from strong-field gravitational lensing
AU - Chan, Chi Kwan
AU - Psaltis, Dimitrios
AU - �zel, Feryal
AU - Medeiros, Lia
AU - Marrone, Daniel
AU - Sadowski, Aleksander
AU - Narayan, Ramesh
N1 - Publisher Copyright:
� 2015. The American Astronomical Society. All rights reserved..
PY - 2015/10/20
Y1 - 2015/10/20
N2 - 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.
AB - 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.
KW - Galaxy: center
KW - accretion, accretion disks
KW - black hole physics
KW - radiative transfer
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U2 - 10.1088/0004-637X/812/2/103
DO - 10.1088/0004-637X/812/2/103
M3 - Article
AN - SCOPUS:84946013109
SN - 0004-637X
VL - 812
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 103
ER -