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Simultaneous X-Ray and Infrared Observations of Sagittarius A*'s Variability

Boyce, H. and Haggard, D. and Witzel, G. and Willner, S. P. and Neilsen, J. and Hora, J. L. and Markoff, S. and Ponti, G. and Baganoff, F. and Becklin, E. E. and Fazio, G. G. and Lowrance, P. and Morris, M. R. and Smith, H. A. (2019) Simultaneous X-Ray and Infrared Observations of Sagittarius A*'s Variability. Astrophysical Journal, 871 (2). Art. No. 161. ISSN 1538-4357. PMCID PMC7440390. doi:1538-4357/aaf71f.

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Emission from Saggitarius A* is highly variable at both X-ray and infrared (IR) wavelengths. Observations over the last ~20 yr have revealed X-ray flares that rise above a quiescent thermal background about once per day, while faint X-ray flares from Sgr A* are undetectable below the constant thermal emission. In contrast, the IR emission of Sgr A* is observed to be continuously variable. Recently, simultaneous observations have indicated a rise in IR flux density around the same time as every distinct X-ray flare, while the opposite is not always true (peaks in the IR emission may not be coincident with an X-ray flare). Characterizing the behavior of these simultaneous X-ray/IR events and measuring any time lag between them can constrain models of Sgr A*'s accretion flow and the flare emission mechanism. Using 100+ hours of data from a coordinated campaign between the Spitzer Space Telescope and the Chandra X-ray Observatory, we present results of the longest simultaneous IR and X-ray observations of Sgr A* taken to date. The cross-correlation between the IR and X-ray light curves in this unprecedented data set, which includes four modest X-ray/IR flares, indicates that flaring in the X-ray may lead the IR by approximately 10–20 min with 68% confidence. However, the 99.7% confidence interval on the time-lag also includes zero, i.e., the flaring remains statistically consistent with simultaneity. Long-duration and simultaneous multi-wavelength observations of additional bright flares will improve our ability to constrain the flare timing characteristics and emission mechanisms, and must be a priority for Galactic Center observing campaigns.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle Paper
Boyce, H.0000-0002-6530-5783
Haggard, D.0000-0001-6803-2138
Witzel, G.0000-0003-2618-797X
Willner, S. P.0000-0002-9895-5758
Neilsen, J.0000-0002-8247-786X
Hora, J. L.0000-0002-5599-4650
Markoff, S.0000-0001-9564-0876
Ponti, G.0000-0003-0293-3608
Baganoff, F.0000-0003-3852-6545
Fazio, G. G.0000-0002-0670-0708
Lowrance, P.0000-0001-8014-0270
Morris, M. R.0000-0002-6753-2066
Additional Information:© 2019. The American Astronomical Society. Received 2018 September 13; revised 2018 November 29; accepted 2018 December 7; published 2019 January 29. The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory and the Spitzer Space Telescope. We thank the Chandra and Spitzer scheduling, data processing, and archive teams for making these observations possible. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO7-18135B issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. D.H. acknowledges support from a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant and a Fonds de recherche du Québec–Nature et Technologies (FRQNT) Nouveaux Chercheurs Grant. G.W. acknowledges support from the NSF grants AST-0909218, AST-1412615. J.L.H. acknowledges support from NASA Grant 80NSSC18K0416. G.P. acknowledges financial support from BMWi/DLR grants FKZ 50 OR 1604, 50 OR 1715 and 50 OR 1812. Facilities: Spitzer/IRAC - , Chandra/ACIS. - Software: CIAO Fruscione et al. (2006), NumPy (Jones et al. 2015), AstroPy (The Astropy Collaboration et al. 2018), Matplotlib (Hunter 2007), Bayesian Blocks (Williams et al. 2017), ZDCF (Alexander 2013).
Errata:H. Boyce et al 2021 ApJ 912 168
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Fonds de recherche du Québec – Nature et technologies (FRQNT)UNSPECIFIED
Bundesministerium für Wirtschaft und Technologie (BMWi)FKZ 50 OR 1604
Bundesministerium für Wirtschaft und Technologie (BMWi)50 OR 1715
Bundesministerium für Wirtschaft und Technologie (BMWi)50 OR 1812
Deutsches Zentrum für Luft- und Raumfahrt (DLR)UNSPECIFIED
Subject Keywords:accretion, accretion disks; black hole physics; Galaxy: center; radiation mechanisms: non-thermal
Issue or Number:2
PubMed Central ID:PMC7440390
Record Number:CaltechAUTHORS:20190130-121936992
Persistent URL:
Official Citation:H. Boyce et al 2019 ApJ 871 161
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92527
Deposited By: George Porter
Deposited On:31 Jan 2019 00:11
Last Modified:17 Feb 2022 19:18

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