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Unprecedented Near-infrared Brightness and Variability of Sgr A*

Do, Tuan and Witzel, Gunther and Gautam, Abhimat K. and Chen, Zhuo and Ghez, Andrea M. and Morris, Mark R. and Becklin, Eric E. and Ciurlo, Anna and Hosek, Matthew, Jr. and Martinez, Gregory D. and Matthews, Keith and Sakai, Shoko and Schödel, Rainer (2019) Unprecedented Near-infrared Brightness and Variability of Sgr A*. Astrophysical Journal Letters, 882 (2). Art. No. L27. ISSN 2041-8213.

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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 μm. 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Do, Tuan0000-0001-9554-6062
Witzel, Gunther0000-0003-2618-797X
Gautam, Abhimat K.0000-0002-2836-117X
Chen, Zhuo0000-0002-3038-3896
Ghez, Andrea M.0000-0003-3230-5055
Morris, Mark R.0000-0002-6753-2066
Ciurlo, Anna0000-0001-5800-3093
Hosek, Matthew, Jr.0000-0003-2874-1196
Martinez, Gregory D.0000-0002-7476-2521
Sakai, Shoko0000-0001-5972-663X
Alternate Title:Unprecedented variability of Sgr A* in NIR
Additional Information:© 2019 The American Astronomical Society. Received 2019 June 28; revised 2019 July 19; accepted 2019 July 29; published 2019 September 11. We thank the anonymous referee for helpful comments. We thank the staff and astronomers at Keck Observatory especially Jim Lyke, Randy Campbell, Sherry Yeh, Greg Doppmann, Cynthia Wilburn, Terry Stickel, and Alan Hatakeyama. Support for this work was provided by NSF AAG grant AST-1412615, the W. M. Keck Foundation, the Heising-Simons Foundation, the Gordon and Betty Moore Foundation, the Levine-Leichtman Family Foundation, the Preston Family Graduate Fellowship (held by A.G.), and the UCLA Galactic Center Star Society. R.S. has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement No. 614922. R.S. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). This research was based on data products from the Galactic Center Orbits Initiative, which is hosted at UCLA and is a key science program of the Galactic Center Collaboration. The W.M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize that the summit of Maunakea has always held a very significant cultural role for the indigenous Hawaiian community. We are most fortunate to have the opportunity to observe from this mountain.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Heising-Simons FoundationUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Levine-Leichtman Family FoundationUNSPECIFIED
Preston Family Graduate FellowshipUNSPECIFIED
European Research Council (ERC)614922
Severo OchoaSEV-2017-0709
Subject Keywords:Supermassive black holes; Low-luminosity active galactic nuclei; Near infrared astronomy; Galactic center
Issue or Number:2
Classification Code:Supermassive black holes (1663); Low-luminosity active galactic nuclei (2033); Near infrared astronomy (1093); Galactic center (565)
Record Number:CaltechAUTHORS:20190911-130643745
Persistent URL:
Official Citation:Tuan Do et al 2019 ApJL 882 L27
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98577
Deposited By: Tony Diaz
Deposited On:11 Sep 2019 23:25
Last Modified:03 Oct 2019 21:42

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