The Circular Polarization of Sagittarius A* at Submillimeter Wavelengths

Abstract

We report the first detections of circularly polarized emission at submillimeter wavelengths from the compact radio source and supermassive black hole candidate Sgr A* at a level of 1.2\pm0.3% at 1.3 mm wavelength (230 GHz) and 1.6\pm0.3% at 860 microns (345 GHz) with the same handedness as observed at lower frequencies (1.4-15 GHz). The observations, taken with the Submillimeter Array in multiple epochs, also show simultaneous linear polarization (LP) at both wavelengths of about 6%. These properties differ sharply from those at wavelengths longer than 1 cm (frequencies below 30 GHz), where weak circular polarization (CP) (~ 0.5%) dominates over LP, which is not detected at similar fractional limits. We describe an extensive set of tests to ensure the accuracy of our measurements. We find no CP in any other source, including the bright quasar 1924-292, which traces the same path on the sky as Sgr A* and therefore should be subject to identical systematic errors originating in the instrument frame. Since a relativistic synchrotron plasma is expected to produce little CP, the observed CP is probably generated close to the event horizon by the Faraday conversion process. We use a simple model to show that the phase shift associated with Faraday conversion can be nearly independent of frequency, a sufficient condition to make the handedness of CP independent of frequency. Because the size of the tau=1-surface changes by more than an order of magnitude between 1.4 and 345 GHz, the magnetic field must be coherent over such scales to consistently produce left CP.

13, pages, 6 figures, 5 tables. Accepted for publication in ApJ

References in corpus (16)

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• Propagation Effects in Magnetized Transrelativistic Plasmas
• The Variability of Polarized Radiation from Sgr A*
• Coordinated NIR/mm observations of flare emission from Sagittarius A*
• Linearly and Circularly Polarized Emission in Sagittarius A*
• Generalized Space-time Noncommutative Inflation
• Constraining Radiatively Inefficient Accretion Flows with Polarization
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• Ab Initio Horizon-Scale Simulations of Magnetically Arrested Accretion in Sagittarius A* Fed by Stellar Winds
• Polarimetric properties of Event Horizon Telescope targets from ALMA
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• Polarimetry and Astrometry of NIR Flares as Event Horizon Scale, Dynamical Probes for the Mass of Sgr A*
• Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
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• ALMA Polarimetry of Sgr A*: Probing the Accretion Flow from the Event Horizon to the Bondi Radius
• Probing the magnetic field structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations
• A parameter survey of Sgr A* radiative models from GRMHD simulations with self-consistent electron heating
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• ALMA Observations of the Terahertz Spectrum of Sagittarius A*
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• Self-consistent spectra from radiative GRMHD simulations of accretion onto Sgr A*
• Probing the innermost accretion flow geometry of Sgr A* with Event Horizon Telescope
• 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
• Polarimetric signatures of hot spots in black hole accretion flows
• Linearly Polarized Millimeter and Submillimeter Continuum Emission of Sgr A* Constrained by ALMA
• Positron Effects on Polarized Images and Spectra from Jet and Accretion Flow Models of M87* and Sgr A*
• Non-Zeeman Circular Polarization of Molecular Rotational Spectral Lines
• The internal Faraday screen of Sagittarius A*
• Relative Astrometry of Compact Flaring Structures in Sgr A* with Polarimetric VLBI
• The 492 GHz emission of Sgr A* constrained by ALMA
• Determining the Composition of Relativistic Jets from Polarization Maps
• Polarization images of accretion flow around supermassive black holes: imprints of toroidal field structure
• Synchrotron Polarization Radiative Transfer: Relativistic Thermal Electrons Contribution
• Circular polarization of cosmic photons due to their interactions with Sterile neutrino dark matter
• CHANG-ES XI: Circular Polarization in the Cores of Nearby Galaxies
• Polarized signatures of adiabatically expanding hotspots in Sgr A*'s accretion flow
• Non-Zeeman Circular Polarization of Molecular Spectral Lines in the ISM
• Flare emission from Sagittarius A*