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arXiv · 2003.08601

Time Variations in the Flux Density of Sgr A* at 230 GHz Detected with ALMA

Yuhei Iwata·Tomoharu Oka·Masato Tsuboi·Makoto Miyoshi·Shunya Takekawa
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Abstract

A radio source at the Galactic center Sgr A* is a prime supermassive black hole candidate and therefore key to developing our understanding of them. Time variations in the 230 GHz band flux of Sgr A* have been found with the Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 5 observations. Measuring the flux density of Sgr A* in 1 min snapshots at 217.5, 219.5, and 234.0 GHz, we obtained light curves for ten 70 min periods. The light curves show variations at a few tens of minutes and hourly scales. The shorter timescale is similar to the orbital period of the innermost stable circular orbit around a $4\times 10^{6}$ $M_{\odot}$ black hole, suggesting that the variation originates from the immediate vicinity of Sgr A*. We also detected no time lag between 217.5 and 234.0 GHz and a dependence of the spectral index on the flux density.

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Yuhei Iwata, Tomoharu Oka, Masato Tsuboi, Makoto Miyoshi, Shunya Takekawa. 2020-03-19. Time Variations in the Flux Density of Sgr A* at 230 GHz Detected with ALMA. https://doi.org/10.3847/2041-8213/ab800d

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