Narayan, R;
Palumbo, DCM;
Johnson, MD;
Gelles, Z;
Himwich, E;
Chang, DO;
Ricarte, A;
... Zhao, S-S; + view all
(2021)
The Polarized Image of a Synchrotron-emitting Ring of Gas Orbiting a Black Hole.
Astrophysical Journal
, 912
(1)
, Article 35. 10.3847/1538-4357/abf117.
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Abstract
Synchrotron radiation from hot gas near a black hole results in a polarized image. The image polarization is determined by effects including the orientation of the magnetic field in the emitting region, relativistic motion of the gas, strong gravitational lensing by the black hole, and parallel transport in the curved spacetime. We explore these effects using a simple model of an axisymmetric, equatorial accretion disk around a Schwarzschild black hole. By using an approximate expression for the null geodesics derived by Beloborodov and conservation of the Walker–Penrose constant, we provide analytic estimates for the image polarization. We test this model using currently favored general relativistic magnetohydrodynamic simulations of M87*, using ring parameters given by the simulations. For a subset of these with modest Faraday effects, we show that the ring model broadly reproduces the polarimetric image morphology. Our model also predicts the polarization evolution for compact flaring regions, such as those observed from Sgr A* with GRAVITY. With suitably chosen parameters, our simple model can reproduce the EVPA pattern and relative polarized intensity in Event Horizon Telescope images of M87*. Under the physically motivated assumption that the magnetic field trails the fluid velocity, this comparison is consistent with the clockwise rotation inferred from total intensity images.
| Type: | Article |
|---|---|
| Title: | The Polarized Image of a Synchrotron-emitting Ring of Gas Orbiting a Black Hole |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/1538-4357/abf117 |
| Publisher version: | https://doi.org/10.3847/1538-4357/abf117 |
| Language: | English |
| Additional information: | Content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. |
| Keywords: | Science & Technology, Physical Sciences, Astronomy & Astrophysics, M87 EVENT HORIZON, MAGNETIC-FIELD STRUCTURE, SAGITTARIUS-A-ASTERISK, NEAR-INFRARED FLARES, ACCRETION FLOW, MAGNETOHYDRODYNAMIC SIMULATIONS, ARRESTED ACCRETION, DISK, JET, POLARIMETRY |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10137745 |
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