학술논문
Millimeter light curves of Sagittarius A* observed during the 2017 Event Horizon Telescope campaign
Document Type
Working Paper
Author
Wielgus, Maciek; Marchili, Nicola; Marti-Vidal, Ivan; Keating, Garrett K.; Ramakrishnan, Venkatessh; Tiede, Paul; Fomalont, Ed; Issaoun, Sara; Neilsen, Joey; Nowak, Michael A.; Blackburn, Lindy; Gammie, Charles F.; Goddi, Ciriaco; Haggard, Daryl; Lee, Daeyoung; Moscibrodzka, Monika; Tetarenko, Alexandra J.; Bower, Geoffrey C.; Chan, Chi-Kwan; Chatterjee, Koushik; Chesler, Paul M.; Dexter, Jason; Doeleman, Sheperd S.; Georgiev, Boris; Gurwell, Mark; Johnson, Michael D.; Marrone, Daniel P.; Mus, Alejandro; Psaltis, Dimitrios; Ripperda, Bart; Collaboration, Gunther Witzel + the Event Horizon Telescope
Source
The Astrophysical Journal Letters, 930:L19 (2022)
Subject
Language
Abstract
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 millimeter 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 min and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 h. 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.