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Infrared/X-ray intensity variations and the color of Sgr A*

Hornstein, S. D. and Matthews, K. and Ghez, A. M. and Lu, J. R. and Morris, M. and Becklin, E. and Baganoff, F. K. and Rafelski, M. (2006) Infrared/X-ray intensity variations and the color of Sgr A*. Journal of Physics: Conference Series, 54 . pp. 399-405. ISSN 1742-6596. doi:10.1088/1742-6596/54/1/063.

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We report the frst time-series measurements of Sgr A*-IR's broadband infrared color. Using the newly commissioned laser guide star adaptive optics (LGS AO) system on the Keck II telescope, we imaged Sgr A*-IR, in the broadband liters H (1.6 μm), K' (2.1 μm), and L' (3.8 μm) every 3 minutes over the course of 120 minutes, during which time the Chandra X-ray Observatory was also monitoring the Galactic center. Complementary measurements of Sgr A*'s L'- and Ms (4.7 μm)-band flux densities were obtained on a separate night with the natural guide star AO system. During our observations, Sgr A*-IR,'s flux density showed a wide range of values (2 to 12 mjy at 2.1 μm), which are associated with at least 4 peaks in the infrared emission and are among its highest infrared flux density measurements. However, all our near-infrared color measurements are consistent with a constant spectral slope of α = -0.9 ± 0.2 (Fν propto να), independent of intensity, wavelength, time, or outburst. Assuming that the infrared wavelengths probe synchrotron emission, we interpret the lack of variation in the infrared spectral index as an indication that the acceleration mechanism leaves the distribution of the bulk of the electrons responsible for the infrared emission unchanged. During our coordinated infrared observations, no elevated X-ray emission was detected. While the less frequent X-ray outbursts have shown correlated emission in previous studies, the lack of X-ray variation during the significant infrared variations reported here indicates that one may not be able to connect the infrared and X-ray emission to the same electrons. We suggest that while the acceleration mechanism leaves the bulk of the electron energy distribution unchanged, it generates a variable high-energy tail. It is this high-energy tail that gives rise to the less frequent X-ray outbursts.

Item Type:Article
Related URLs:
URLURL TypeDescription
Ghez, A. M.0000-0003-3230-5055
Lu, J. R.0000-0001-9611-0009
Morris, M.0000-0002-6753-2066
Rafelski, M.0000-0002-9946-4731
Additional Information:© Institute of Physics and IOP Publishing Limited 2006. Support for this work was provided by NSF grant AST 04-06816 and the NSF Science and Technology Center for Adaptive Optics, managed by UCSC (AST 98-76783). FKB was supported by NASA through Chandra award G05-6093X. The data presented herein were obtained at the W.M. Keck Observatory, which 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. Galactic Center Workshop 2006 — From the Center of the Milky Way to Nearby Low-Luminosity Galactic Nuclei, Bad Honnef, Germany, 18 to 22 April 2006. Journal of Physics: Conference Series, Volume 54, 2006.
Funding AgencyGrant Number
NSFAST 04-06816
NSFAST 98-76783
W. M. Keck FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:HORjpcs06
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ID Code:6908
Deposited By: Archive Administrator
Deposited On:02 Jan 2007
Last Modified:12 Jul 2022 19:42

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