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Unprecedented Near-infrared Brightness and Variability of Sgr A*

Tuan DoUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]Gunther WitzelMax Planck Institute for Radio Astronomy, Auf dem Hügel 69, D-53121 Bonn (Endenich), GermanyAbhimat K. GautamUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]Zhuo ChenUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]A. M. GhezUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]M. MorrisUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]Eric E. BecklinUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]Anna CiurloUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]Matthew HosekUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]Gregory D. MartinezUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]Keith MatthewsDivision of Physics, Mathematics, and Astronomy, California Institute of Technology, MC 301-17, Pasadena, CA 91125, USAShoko SakaiUCLA Galactic Center Group, Physics and Astronomy Department, University of California, Los Angeles, CA 90024, USA; [email protected]Rainer SchödelInstituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas, Glorieta de la Astronomía S/N, E-18008 Granada, Spain

2019en

ABI

Annotatsiya

Abstract The electromagnetic counterpart to the Galactic center supermassive black hole, Sgr A*, has been observed in the near-infrared for over 20 yr and is known to be highly variable. We report new Keck Telescope observations showing that Sgr A* reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths. In the K ′ band, Sgr A* reached flux levels of ∼6 mJy, twice the level of the previously observed peak flux from >13,000 measurements over 130 nights with the Very Large Telescope and Keck Telescopes. We also observe a factor of 75 change in flux over a 2 hr time span with no obvious color changes between 1.6 and 2.1 μ m. The distribution of flux variations observed this year is also significantly different than the historical distribution. Using the most comprehensive statistical model published, the probability of a single night exhibiting peak flux levels observed this year, given historical Keck observations, is less than 0.3%. The probability of observing flux levels that are similar to all four nights of data in 2019 is less than 0.05%. This increase in brightness and variability may indicate a period of heightened activity from Sgr A* or a change in its accretion state. It may also indicate that the current model is not sufficient to model Sgr A* at high flux levels and should be updated. Potential physical origins of Sgr A*'s unprecedented brightness may be from changes in the accretion flow as a result of the star S0-2's closest passage to the black hole in 2018, or from a delayed reaction to the approach of the dusty object G2 in 2014. Additional multi-wavelength observations will be necessary to both monitor Sgr A* for potential state changes and to constrain the physical processes responsible for its current variability.

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DOI: 10.3847/2041-8213/ab38c3

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