Probing the Magnetic Field Structure in on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

Abstract

Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic field structure that controls these phenomena remains uncertain. We perform general relativistic (GR) polarized radiative transfer of time-dependent three-dimensional GR magnetohydrodynamical simulations to model thermal synchrotron emission from the Galactic Center source SagittariusA * (SgrA * ). We compare our results to new polarimetry measurements by the Event Horizon Telescope (EHT) and show how polarization in the visibility (Fourier) domain distinguishes and constrains accretion flow models with different magnetic field structures. These include models with small-scale fields in disks driven by the magnetorotational instability as well as models with large-scale ordered fields in magnetically arrested disks. We also consider different electron temperature and jet mass-loading prescriptions that control the brightness of the disk, funnel-wall jet, and Blandford-Znajek-driven funnel jet. Our comparisons between the simulations and observations favor models with ordered magnetic fields near the black hole event horizon in SgrA * , though both disk-and jet-dominated emission can satisfactorily explain most of the current EHT data. We also discuss how the black hole shadow can be filled-in by jet emission or mimicked by the absence of funnel jet emission. We show that stronger model constraints should be possible with upcoming circular polarization and higher frequency (349 GHz) measurements.

Modeling Polarized Emission from Black Hole Jets: Application to M87 Core Jet

“…Until recently, the least understood part of these models was a proper treatment of radiating electrons. Finally, however, this issue has been addressed [13][14][15][16][17][18][19]. With new and more detailed observations, we are beginning to directly compare the numerical simulations of accretion flows to real astronomical systems such as Galactic center Sgr A* and the core of M87 galaxy [20].…”

Observational Signatures of Mass-loading in Jets Launched by Rotating Black Holes

“…Recently, Gold et al (2017) argued that the prescription used for treating the funnel material could be very important when interpreting future observations from the EHT. In particular, they showed that the black hole shadow can be completely obscured in the case of significant emission from the funnel, while the absence of strong funnel emission can in fact mimic features of the shadow.…”

“…In recent years, MAD and SANE GRMHD models have been used extensively to model Sgr A * , the extremely lowluminosity accreting supermassive black hole at the center of our Galaxy (Mościbrodzka et al , 2014Shcherbakov et al 2012;Mościbrodzka & Falcke 2013;Chan et al 2015aChan et al , 2015bBall et al 2016;Gold et al 2017;Ressler et al 2017). These studies have largely been motivated by very-long baseline interferometric observations with the Event Horizon Telescope (EHT; Doeleman et al 2009a), which will soon resolve the structure in Sgr A * on spatial scales comparable to the Schwarzschild radius.…”

Time Domain Filtering of Resolved Images of Sgr A∗

“…Widely available relativistic radiative transfer schemes (e.g. Noble et al 2007;Dolence et al 2009;Shcherbakov & McKinney 2013;Schnittman & Krolik 2013;Chan et al 2015b;Dexter 2016;Narayan et al 2016;Gold et al 2017) can, given accurate information about the electron distribution function, now produce mock images, polarization maps, and spectra of model accretion flows.…”