How narrow is the M87* ring? I. The choice of closure likelihood function

Abstract

Event Horizon Telescope (EHT) observations of the core of the galaxy M87 suggest an observational appearance dominated by a ring of approximately 40$\mu$as in diameter. The thickness of the ring is less certain: imaging efforts constrained it to be less than half the diameter (consistent with an imaging resolution of 20$\mu$as), while visibility-domain modeling suggested a variety of fractional widths, including as low as $10\%$ on some days. The fractional width is very interesting as it has the potential to discriminate between different astrophysical scenarios for the source; in fact, the $10$--$20\%$ range is so narrow as to be in tension with theoretical expectations. In the first of a series of papers on the width of the observed ring, we reproduce a subset of EHT visibility-domain modeling results and we explore whether alternative data analysis methods might favor thicker rings. We point out that the closure phase (and closure amplitude) likelihood function is not independent of residual station gain amplitudes, even at high signal-to-noise, and explore two approximations of practical interest: one standard in the field (and employed by the EHT collaboration), and a new one that we propose. Analyzing the public data, we find that the new likelihood approximation prefers somewhat thicker rings, more in line with theoretical expectations. Further analysis is needed, however, to determine which approximation is better for the EHT data.

References in corpus (33)

• emcee: The MCMC Hammer
• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
• Advection-Dominated Accretion: A Self-Similar Solution
• dynesty: A Dynamic Nested Sampling Package for Estimating Bayesian Posteriors and Evidences
• 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
• Viewing the Shadow of the Black Hole at the Galactic Center
• First M87 Event Horizon Telescope Results. II. Array and Instrumentation
• First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
• Black Hole Shadows, Photon Rings, and Lensing Rings
• General Relativistic Magnetohydrodynamic Simulations of Jet Formation and Large-Scale Propagation from Black Hole Accretion Systems
• The Black-Hole Mass in M87 from Gemini/NIFS Adaptive Optics Observations
• Universal Interferometric Signatures of a Black Hole's Photon Ring
• The M87 Black Hole Mass from Gas-dynamical Models of Space Telescope Imaging Spectrograph Observations
• Electrodynamics of black hole magnetospheres
• The Shape of the Black Hole Photon Ring: A Precise Test of Strong-Field General Relativity
• Lensing by Kerr Black Holes
• First-Principles Plasma Simulations of Black-Hole Jet Launching
• Observing the Inner Shadow of a Black Hole: A Direct View of the Event Horizon
• Dos and don'ts of reduced chi-squared
• Parabolic Jets from the Spinning Black Hole in M87
• Spacetime approach to force-free magnetospheres
• The Null Geodesics of the Kerr Exterior
• Can the EHT M87 results be used to test general relativity?
• Horizon-Scale Lepton Acceleration in Jets: Explaining the Compact Radio Emission in M87
• Black Hole Magnetospheres
• Monitoring the Morphology of M87* in 2009-2017 with the Event Horizon Telescope
• Closure statistics in interferometric data
• Measuring Spin from Relative Photon Ring Sizes
• Maximum Observable Blueshift from Circular Equatorial Kerr Orbiters
• Reconstruction of Static Black Hole Images Using Simple Geometric Forms
• Interferometric Closure Phase Uncertainties in the Low Signal-to-Noise Ratio Regime