02935nas a2200469   4500000000100000000000100001008004100002100001900043700002000062700002300082700002300105700002800128700001500156700001700171700001700188700002100205700002000226700001800246700001800264700001700282700002400299700002700323700002200350700001800372700002300390700002000413700001700433700002400450700001900474700001700493700002300510700002200533700001800555700002200573700001900595700004600614245010400660856004500764300000900809490000800818520163900826       2022                            d1 aMaciek Wielgus1 aNicola Marchili1 aIván Martí-Vidal1 aGarrett K. Keating1 aVenkatessh Ramakrishnan1 aPaul Tiede1 aSara Issaoun1 aJoey Neilsen1 aMichael A. Nowak1 aLindy Blackburn1 aCiriaco Goddi1 aDaryl Haggard1 aDaeyoung Lee1 aMonika Moscibrodzka1 aAlexandra J. Tetarenko1 aGeoffrey C. Bower1 aChi-Kwan Chan1 aKoushik Chatterjee1 aPaul M. Chesler1 aJason Dexter1 aSheperd S. Doeleman1 aBoris Georgiev1 aMark Gurwell1 aMichael D. Johnson1 aDaniel P. Marrone1 aAlejandro Mus1 aDimitrios Psaltis1 aGunther Witzel1 aThe Event Horizon Telescope Collaboration00aMillimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign  uhttps://doi.org/10.3847/2041-8213/ac6428  a1-320 v9303 a<p>	The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in the Galactic Center on 2017 April 5-11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array were collected, providing Sgr A* light curves simultaneous with the EHT observations. These data sets, complementing the EHT very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for Sgr A* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. While most of the light curves correspond to a low variability state of Sgr A*, the April 11 observations follow an X-ray flare and exhibit strongly enhanced variability. All of the light curves are consistent with a red-noise process, with a power spectral density (PSD) slope measured to be between -2 and -3 on timescales between 1 minute and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 hr. The spectral energy distribution is flat at 220 GHz, and there are no time lags between the 213 and 229 GHz frequency bands, suggesting low optical depth for the event horizon scale source. We characterize Sgr A*'s variability, highlighting the different behavior observed just after the X-ray flare, and use Gaussian process modeling to extract a decorrelation timescale and a PSD slope. We also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines.</p>