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

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.

8 pages, 3 figures, 1 table, accepted for publication in ApJL

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Cited by in corpus (16)

• First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• Millimeter light curves of Sagittarius A* observed during the 2017 Event Horizon Telescope campaign
• Rapid Variability of Sgr A* across the Electromagnetic Spectrum
• Second Scale Submillimeter Variability of Sagittarius A* during flaring activity of 2019: On the Origin of Bright Near Infrared Flares
• The internal Faraday screen of Sagittarius A*
• The jet and resolved features of the central supermassive black hole of M 87 observed with EHT
• Multi-wavelength Variability of Sagittarius A* in July 2019
• Testing the linear relationship between black hole mass and variability timescale in low-luminosity AGN at submillimeter wavelengths
• A first search of transients in the Galactic Center from 230 GHz ALMA observations
• Photon emission from inside the innermost stable circular orbit
• Detection of a 20 minute time lag observed from Sgr A* between 8 and 10 GHz with the VLA
• ALMA Astrometry of the Objects within 0.5 pc of Sagittarius A${}^{\ast }$
• Photon escape in the extremal Kerr black hole spacetime
• Doppler Boosting of the S-stars in the Galactic Center
• Variability of Sagittarius A* at 3 GHz on minute-scale with MeerKAT
• Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign