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Rapid Variability of Sgr A* across the Electromagnetic Spectrum

Gunther WitzelMax-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121, Bonn, GermanyGregory D. MartinezDepartment of Physics and Astronomy, University of California, Los Angeles, Box 951547, Los Angeles, CA 90095-1547, USAS. P. WillnerCenter for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USAE. E. BecklinDepartment of Physics and Astronomy, University of California, Los Angeles, Box 951547, Los Angeles, CA 90095-1547, USAHope BoyceDepartment of Physics, McGill University, 3600 University St., Montreal, QC H3A 2T8, CanadaTuan DoDepartment of Physics and Astronomy, University of California, Los Angeles, Box 951547, Los Angeles, CA 90095-1547, USAA. EckartI. Physikalisches Institut, Universität zu Köln Zülpicher Str. 77 D-50937 Köln, GermanyG. G. FazioCenter for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USAA. M. GhezDepartment of Physics and Astronomy, University of California, Los Angeles, Box 951547, Los Angeles, CA 90095-1547, USAMark GurwellCenter for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USADaryl HaggardDepartment of Physics, McGill University, 3600 University St., Montreal, QC H3A 2T8, CanadaR. Herrero‐IllanaEuropean Southern Observatory (ESO), Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, ChileJoseph L. HoraCenter for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USAZhiyuan 志远 Li 李School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023 Jiangsu, People’s Republic of ChinaM. KrämerMax-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121, Bonn, GermanyN. MarchiliIstituto di Radioastronomia—INAF, Via Piero Gobetti 101, I-40129, Bologna, ItalyM. MorrisDepartment of Physics and Astronomy, University of California, Los Angeles, Box 951547, Los Angeles, CA 90095-1547, USAH. A. SmithCenter for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USAM. SubroweitI. Physikalisches Institut, Universität zu Köln Zülpicher Str. 77 D-50937 Köln, GermanyJ. A. ZensusI. Physikalisches Institut, Universität zu Köln Zülpicher Str. 77 D-50937 Köln, Germany

2021en

ABI

Annotatsiya

Abstract Sagittarius A* (Sgr A*) is the variable radio, near-infrared (NIR), and X-ray source associated with accretion onto the Galactic center black hole. We have analyzed a comprehensive submillimeter (including new observations simultaneous with NIR monitoring), NIR, and 2–8 keV data set. Submillimeter variations tend to lag those in the NIR by ∼30 minutes. An approximate Bayesian computation fit to the X-ray first-order structure function shows significantly less power at short timescales in the X-rays than in the NIR. Less X-ray variability at short timescales, combined with the observed NIR–X-ray correlations, means the variability can be described as the result of two strictly correlated stochastic processes, the X-ray process being the low-pass-filtered version of the NIR process. The NIR–X-ray linkage suggests a simple radiative model: a compact, self-absorbed synchrotron sphere with high-frequency cutoff close to NIR frequencies plus a synchrotron self-Compton scattering component at higher frequencies. This model, with parameters fit to the submillimeter, NIR, and X-ray structure functions, reproduces the observed flux densities at all wavelengths, the statistical properties of all light curves, and the time lags between bands. The fit also gives reasonable values for physical parameters such as magnetic flux density B ≈ 13 G, source size L ≈ 2.2 R S , and high-energy electron density n e ≈ 4 × 10 7 cm −3 . An animation illustrates typical light curves, and we make public the parameter chain of our Bayesian analysis, the model implementation, and the visualization code.

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DOI: 10.3847/1538-4357/ac0891

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