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SUMMARY:Inferring the Black Hole and Accretion Parameters of Sagittarius A
 * from EHT Observations Using a Semianalytic Model
DTSTART;VALUE=DATE-TIME:20261028T170500Z
DTEND;VALUE=DATE-TIME:20261028T171500Z
DTSTAMP;VALUE=DATE-TIME:20261028T201754Z
UID:indico-contribution-3637@nyx.physics.mcgill.ca
DESCRIPTION:Speakers: Braden J. Marazzo-Nowicki (McGill University Departm
 ent of Physics)\nThe Event Horizon Telescope (EHT) Collaboration produced 
 the first image of the apparent shadow of the central black hole of Sagitt
 arius A$^*$ (Sgr A$^*$). Sgr A$^*$ source structure varies significantly o
 n timescales shorter than the duration of an observation\, preventing impr
 oved data coverage through Earth rotation aperture synthesis. This rapid v
 ariability provides the opportunity to quantify intrinsic variability and 
 separate time-variable emission features from stable signatures of strong 
 gravity and the accretion environment. To infer unknown properties of Sgr 
 A$^*$ and its surrounding accretion flow\, we perform Bayesian inference o
 n a series of EHT data segments ("snapshots"). We directly fit parameters 
 of a semianalytic emission model jointly with complex station gains to sna
 pshot visibilities\, then extract estimates of the time-averaged\, persist
 ent source structure and temporal variability by stacking snapshots in a B
 ayesian hierarchical model. This approach successfully reproduces paramete
 rs of general relativistic magnetohydrodynamic simulations using synthetic
  EHT observations. Even with physically motivated assumptions about the Sg
 r A$^*$ environment\, black hole spin and magnetic field parameters are po
 orly constrained by 2017 EHT observations. Our inference constrains other 
 parameters\, favoring a nearly face-on observer inclination ($\\theta_{\\r
 m o} = 9.2^\\circ \\pm 3.6 ^\\circ \\pm_{\\rm v} 11.6^\\circ$)\, an emissi
 on peak near the horizon ($R_{\\rm peak} = 4.9 \\pm 0.1 \\pm_{\\rm v} 0.5\
 \\,GM/c^2$)\, near-northern projected spin position angle ($p.a. = 7.3^\\c
 irc \\pm 7.08 ^\\circ \\pm_{\\rm v} 43.5^\\circ$ counterclockwise from ver
 tical)\, and dominant emission $43.4^\\circ \\pm 2.0^\\circ \\pm_{\\rm v} 
 5.9^\\circ$ above the equatorial plane\, where we separate average structu
 re uncertainty ($\\pm$) from the impacts of temporal variability and model
  misspecification ($\\pm_{\\rm v}$).\n\nhttps://nyx.physics.mcgill.ca/even
 t/587/contributions/3637/
LOCATION:Online 
URL:https://nyx.physics.mcgill.ca/event/587/contributions/3637/
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