Linearly Polarized Millimeter and Submillimeter Continuum Emission of Sgr A* Constrained by ALMA

Abstract

Our aim is to characterize the polarized continuum emission properties including intensity, polarization position angle, and polarization percentage of Sgr A* at $\sim$100 (3.0 mm), $\sim$230 (1.3 mm), $\sim$345 (0.87 mm), $\sim$500 (0.6 mm), and $\sim$700 GHz (0.43 mm). We report continuum emission properties of Sgr A* at the above frequency bands, based on the Atacama Large Millimeter Array (ALMA) observations. We measured flux densities of Sgr A* from ALMA single pointing and mosaic observations. We performed sinusoidal fittings to the observed (XX-YY)/I intensity ratios, to derive the polarization position angles and polarization percentages. We successfully detect polarized continuum emission from all observed frequency bands. We observed lower Stokes I intensity at $\sim$700 GHz than that at $\sim$500 GHz, which suggests that emission at $\gtrsim$500 GHz is from optically thin part of a synchrotron emission spectrum. Both the Stokes I intensity and the polarization position angle at our highest observing frequency of $\sim$700 GHz, may be varying with time. However, we do not yet detect variation in the polarization percentage at $>$500 GHz. The polarization percentage at $\sim$700 GHz is likely lower than that at $\sim$500 GHz. By comparing the $\sim$500 GHz and $\sim$700 GHz observations with the observations at lower frequency bands, we suggest that the intrinsic polarization position angle of Sgr A* is varying with time. This paper also reports the measurable polarization properties from the observed calibration quasars. The future simultaneous multi-frequency polarization observations are required for clarifying the time and frequency variation of polarization position angle and polarization percentage.

11 pages, 10 figures, submitted to A&A; first referee report received. arXiv admin note: text overlap with arXiv:1604.00599

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• ALMA Polarimetry of Sgr A*: Probing the Accretion Flow from the Event Horizon to the Bondi Radius
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• Constraining particle acceleration in Sgr A* with simultaneous GRAVITY, Spitzer, NuSTAR and Chandra observations
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• Positron Effects on Polarized Images and Spectra from Jet and Accretion Flow Models of M87* and Sgr A*
• Probing spacetime and accretion model for the Galactic Center: Comparison of Kerr and dilaton black hole shadows
• The internal Faraday screen of Sagittarius A*
• A nonthermal bomb explains the near-infrared superflare of Sgr A*
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• Synchrotron Polarization Radiative Transfer: Relativistic Thermal Electrons Contribution
• Effects of Hydrogen vs. Helium on Electromagnetic Black Hole Observables
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• Synchrotron Polarization of Relativistic Thermal Electrons
• The Effects of Tilt on the Time Variability of Millimeter and Infrared Emission from Sagittarius A*
• ALMA full polarization observations of PKS1830-211 during its record-breaking flare of 2019
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