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Boyce H, Haggard D, Witzel G, Willner SP, Neilsen J, Hora JL, Markoff S, Ponti G, Baganoff F, Becklin EE, Fazio GG, Lowrance P, Morris MR, Smith HA. Simultaneous X-Ray and Infrared Observations of Sagittarius A*'s Variability. THE ASTROPHYSICAL JOURNAL 2019; 871:161. [PMID: 32831351 PMCID: PMC7440390 DOI: 10.3847/1538-4357/aaf71f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
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.
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Affiliation(s)
- H Boyce
- Department of Physics and McGill Space Institute, McGill University, 3600 University St., Montreal QC, H3A 2T8, Canada
| | - D Haggard
- Department of Physics and McGill Space Institute, McGill University, 3600 University St., Montreal QC, H3A 2T8, Canada
- CIFAR Azrieli Global Scholar, Gravity & the Extreme Universe Program, Canadian Institute for Advanced Research, 661 University Ave., Suite 505, Toronto, Ontario M5G 1M1, Canada
| | - G Witzel
- University of California, Los Angeles, CA 90095, USA
- Max Planck Institute for Radio Astronomy, Bonn, Germany
| | - S P Willner
- Center for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA02138, USA
| | - J Neilsen
- Kavli Institute for Astrophysics & Space Research, MIT, 70 Vassar St., Cambridge, MA 02139, USA
| | - J L Hora
- Center for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA02138, USA
| | - S Markoff
- Anton Pannekoek Institute for Astronomy/GRAPPA, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
| | - G Ponti
- Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, D-85748 Garching, Germany
| | - F Baganoff
- Massachusetts Institute of Technology, 77 Massachusetts Avenue, 37-555, Cambridge, MA 02139, USA
| | - E E Becklin
- University of California, Los Angeles, CA 90095, USA
| | - G G Fazio
- Center for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA02138, USA
| | - P Lowrance
- IPAC-Spitzer, MC 314-6, California Institute of Technology, Pasadena, CA 91125, USA
| | - M R Morris
- University of California, Los Angeles, CA 90095, USA
| | - H A Smith
- Center for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA02138, USA
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