@article{discovery10190893, year = {2024}, title = {First Sagittarius A* Event Horizon Telescope Results. VIII. Physical Interpretation of the Polarized Ring}, number = {2}, journal = {The Astrophysical Journal Letters}, note = {Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence, https://creativecommons.org/licenses/by/4.0/. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.}, publisher = {American Astronomical Society}, volume = {964}, month = {April}, issn = {2041-8205}, abstract = {In a companion paper, we present the first spatially resolved polarized image of Sagittarius A* on event horizon scales, captured using the Event Horizon Telescope, a global very long baseline interferometric array operating at a wavelength of 1.3 mm. Here we interpret this image using both simple analytic models and numerical general relativistic magnetohydrodynamic (GRMHD) simulations. The large spatially resolved linear polarization fraction (24\%-28\%, peaking at {$\sim$}40\%) is the most stringent constraint on parameter space, disfavoring models that are too Faraday depolarized. Similar to our studies of M87*, polarimetric constraints reinforce a preference for GRMHD models with dynamically important magnetic fields. Although the spiral morphology of the polarization pattern is known to constrain the spin and inclination angle, the time-variable rotation measure (RM) of Sgr A* (equivalent to {$\approx$}46o {$\pm$} 12o rotation at 228 GHz) limits its present utility as a constraint. If we attribute the RM to internal Faraday rotation, then the motion of accreting material is inferred to be counterclockwise, contrary to inferences based on historical polarized flares, and no model satisfies all polarimetric and total intensity constraints. On the other hand, if we attribute the mean RM to an external Faraday screen, then the motion of accreting material is inferred to be clockwise, and one model passes all applied total intensity and polarimetric constraints: a model with strong magnetic fields, a spin parameter of 0.94, and an inclination of 150o. We discuss how future 345 GHz and dynamical imaging will mitigate our present uncertainties and provide additional constraints on the black hole and its accretion flow.}, url = {http://dx.doi.org/10.3847/2041-8213/ad2df1}, author = {Akiyama, K and Alberdi, A and Alef, W and Algaba, JC and Anantua, R and Asada, K and Azulay, R and Bach, U and Baczko, AK and Ball, D and Balokovi{\'c}, M and Bandyopadhyay, B and Barrett, J and Baub{\"o}ck, M and Benson, BA and Bintley, D and Blackburn, L and Blundell, R and Bouman, KL and Bower, GC and Boyce, H and Bremer, M and Brinkerink, CD and Brissenden, R and Britzen, S and Broderick, AE and Broguiere, D and Bronzwaer, T and Bustamante, S and Byun, DY and Carlstrom, JE and Ceccobello, C and Chael, A and Chan, CK and Chang, DO and Chatterjee, K and Chatterjee, S and Chen, MT and Chen, Y and Cheng, X and Cho, I and Christian, P and Conroy, NS and Conway, JE and Cordes, JM and Crawford, TM and Crew, GB and Cruz-Osorio, A and Cui, Y and Dahale, R and Davelaar, J and De Laurentis, M and Deane, R and Dempsey, J and Desvignes, G and Dexter, J and Dhruv, V and Dihingia, IK and Doeleman, SS and Dougall, S and Dzib, SA and Eatough, RP and Emami, R and Falcke, H and Farah, J and Fish, VL and Fomalont, E and Ford, HA and Foschi, M and Fraga-Encinas, R and Freeman, WT and Friberg, P and Fromm, CM and Fuentes, A and Galison, P and Gammie, CF and Garc{\'i}a, R and Gentaz, O and Georgiev, B and Goddi, C and Gold, R and G{\'o}mez-Ruiz, AI and G{\'o}mez, JL and Gu, M and Gurwell, M and Hada, K and Haggard, D and Haworth, K and Hecht, MH and Hesper, R and Heumann, D and Ho, LC and Ho, P and Honma, M and Huang, CWL and Huang, L and Hughes, DH and Ikeda, S and Violette Impellizzeri, CM and Inoue, M} }