Polarimetric Geometric Modeling for mm-VLBI Observations of Black Holes

Abstract

The Event Horizon Telescope (EHT) is a millimeter very long baseline interferometry (VLBI) array that has imaged the apparent shadows of the supermassive black holes M87* and Sagittarius A*. Polarimetric data from these observations contain a wealth of information on the black hole and accretion flow properties. In this work, we develop polarimetric geometric modeling methods for mm-VLBI data, focusing on approaches that fit data products with differing degrees of invariance to broad classes of calibration errors. We establish a fitting procedure using a polarimetric "m-ring" model to approximate the image structure near a black hole. By fitting this model to synthetic EHT data from general relativistic magnetohydrodynamic models, we show that the linear and circular polarization structure can be successfully approximated with relatively few model parameters. We then fit this model to EHT observations of M87* taken in 2017. In total intensity and linear polarization, the m-ring fits are consistent with previous results from imaging methods. In circular polarization, the m-ring fits indicate the presence of event-horizon-scale circular polarization structure, with a persistent dipolar asymmetry and orientation across several days. The same structure was recovered independently of observing band, used data products, and model assumptions. Despite this broad agreement, imaging methods do not produce similarly consistent results. Our circular polarization results, which imposed additional assumptions on the source structure, should thus be interpreted with some caution. Polarimetric geometric modeling provides a useful and powerful method to constrain the properties of horizon-scale polarized emission, particularly for sparse arrays like the EHT.

34 pages, 15 figures, published in The Astrophysical Journal Letters

References in corpus (32)

• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
• First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
• First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
• First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon
• First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole
• First M87 Event Horizon Telescope Results. VII. Polarization of the Ring
• First Sagittarius A* Event Horizon Telescope Results. III: Imaging of the Galactic Center Supermassive Black Hole
• First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• Revisiting the radio interferometer measurement equation. I. A full-sky Jones formalism
• Key Science Goals for the Next-Generation Event Horizon Telescope
• Millimeter light curves of Sagittarius A* observed during the 2017 Event Horizon Telescope campaign
• Polarimetric properties of Event Horizon Telescope targets from ALMA
• First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization
• The Polarized Image of a Synchrotron Emitting Ring of Gas Orbiting a Black Hole
• Discriminating Accretion States via Rotational Symmetry in Simulated Polarimetric Images of M87
• Radio Circular Polarization Produced in Helical Magnetic Fields in Eight Active Galactic Nuclei
• Monitoring the Morphology of M87* in 2009-2017 with the Event Horizon Telescope
• Resolving the inner parsec of the blazar J1924-2914 with the Event Horizon Telescope
• Decomposing the Internal Faraday Rotation of Black Hole Accretion Flows
• Black Hole Magnetic Fields and Their Imprint on Circular Polarization Images
• Unraveling circular polarimetric images of magnetically arrested accretion flows near event horizon of a black hole
• Observational Signatures of Frame Dragging in Strong Gravity
• How narrow is the M87* ring? II. A new geometric model
• Closure Traces: Novel Calibration-Insensitive Quantities for Radio Astronomy
• Positron Effects on Polarized Images and Spectra from Jet and Accretion Flow Models of M87* and Sgr A*
• CASA on the fringe -- Development of VLBI processing capabilities for CASA
• How Spatially Resolved Polarimetry Informs Black Hole Accretion Flow Models
• MeqSilhouette v2: Spectrally-resolved polarimetric synthetic data generation for the Event Horizon Telescope

Cited by in corpus (7)

• First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization
• A multi-frequency study of sub-parsec jets with the Event Horizon Telescope
• Photon ring polarimetry with next-generation black hole imaging I. M87*
• First VLBI detection of Fornax A
• Prospects of using closure traces directly for imaging in Very Long Baseline Interferometry
• Origin of the ring ellipticity in the black hole images of M87*
• Interferometric Image Reconstruction using Closure Invariants and Machine Learning