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

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 therma...

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Bibliographic Details
Published in:The Astrophysical journal 2019-02, Vol.871 (2), p.161
Main Authors: Boyce, H., Haggard, D., Witzel, G., Willner, S. P., Neilsen, J., Hora, J. L., Markoff, S., Ponti, G., Baganoff, F., Becklin, E. E., Fazio, G. G., Lowrance, P., Morris, M. R., Smith, H. A.
Format: Article
Language:English
Subjects:
Accretion
accretion, accretion disks
Astrophysics
black hole physics
Confidence intervals
Continuously variable
Deposition
Flares
Flux density
Galaxy: center
Light curve
radiation mechanisms: non-thermal
Space telescopes
Thermal emission
Time lag
Wavelengths
X ray telescopes
X-rays
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Summary: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.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aaf71f