# The 492 GHz emission of Sgr A* constrained by ALMA

Liu, HB, Wright, MCH, Zhao, J-H, Mills, EAC, Requena-Torres, MA, Matsushita, S, Martín, S, Ott, J, Morris, MR, Longmore, SN, Brinkerink, CD and Falcke, H (2016) The 492 GHz emission of Sgr A* constrained by ALMA. Astronomy and Astrophysics, 593 (A44). ISSN 0004-6361

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## Abstract

We report linearly polarized continuum emission properties of Sgr A* at $\sim$492 GHz, based on the Atacama Large Millimeter Array (ALMA) observations. We used the observations of the likely unpolarized continuum emission of Titan, and the observations of C\textsc{i} line emission, to gauge the degree of spurious polarization. The Stokes I flux of 3.6$\pm$0.72 Jy during our run is consistent with extrapolations from the previous, lower frequency observations. We found that the continuum emission of Sgr A* at $\sim$492 GHz shows large amplitude differences between the XX and the YY correlations. The observed intensity ratio between the XX and YY correlations as a function of parallactic angle may be explained by a constant polarization position angle of $\sim$158$^{\circ}$$\pm3^{\circ}. The fitted polarization percentage of Sgr A* during our observational period is 14\%\pm1.2\%. The calibrator quasar J1744-3116 we observed at the same night can be fitted to Stokes I = 252 mJy, with 7.9\%\pm0.9\% polarization in position angle P.A. = 4.1^{\circ}$$\pm$4.2$^{\circ}$. The observed polarization percentage and polarization position angle in the present work appear consistent with those expected from longer wavelength observations in the period of 1999-2005. In particular, the polarization position angle at 492 GHz, expected from the previously fitted 167$^{\circ}$$\pm$7$^{\circ}$ intrinsic polarization position angle and (-5.6$\pm$0.7)$\times$10$^{5}$ rotation measure, is 155$^{+9}_{-8}$, which is consistent with our new measurement of polarization position angle within 1$\sigma$. The polarization percentage and the polarization position angle may be varying over the period of our ALMA 12m Array observations, which demands further investigation with future polarization observations.

Item Type: Article astro-ph.HE; astro-ph.HE; astro-ph.GA Q Science > QB Astronomy Astrophysics Research Institute EDP Sciences Author 21 Dec 2016 16:10 04 Sep 2021 13:02 https://researchonline.ljmu.ac.uk/id/eprint/3422

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