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تسجيل مستخدم جديدLinearly Polarized Millimeter and Submillimeter Continuum Emission of Sgr A* Constrained by ALMA
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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.
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