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Long-Term Variations of the Compact Radio Source Sgr A∗ at the Galactic Center

Published online by Cambridge University Press:  23 September 2016

Jun-Hui Zhao ,
R. D. Ekers ,
W. M. Goss ,
K. Y. Lo  and
Ramesh Narayan
Jun-Hui Zhao
Affiliation:
University of New Mexico, Albuquerque, NM 87181
R. D. Ekers
Affiliation:
National Radio Astronomy Observatory, Socorro, NM 87801 Australia Telescope, P. O. Box 76 Epping, NSW 2121, Australia
W. M. Goss
Affiliation:
National Radio Astronomy Observatory, Socorro, NM 87801
K. Y. Lo
Affiliation:
University of Illinois at Urbana-Champaign, Urbana, IL 61801
Ramesh Narayan
Affiliation:
Steward Observatory, Univ. of Arizona, Tucson, AZ 85721

Abstract

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We investigate the long-term flux density variations of the compact radio source Sgr A∗ at the galactic center by combining recent VLA observations with previous Green Bank interferometer data. We present radio flux density light-curves for Sgr A∗ at 20, 11, 6 and 3.7 cm from 1974 to 1987. Long-term variability with a timescale of at least 5 years is seen at 20 cm and there is evidence for more rapid variations at the shorter wavelengths. The variability timescales at 20, 11 and 6 cm fit the λ2 scaling predicted by the theory of refractive scintillation suggesting that the variability could be due to this cause. However, the timescales are relatively short, implying an unusually high velocity in the scattering screen. The modulation index of the variability is large and relatively independent of wavelength.

Type
The Compact Central Objects
Information
Symposium - International Astronomical Union , Volume 136: The Galactic Center , 1989 , pp. 535 - 541
Copyright
Copyright © Kluwer 1989 

References

Balick, B., and Brown, R. L. (1974), Ap. J. 194, 265.Google Scholar
Backer, D. C., 1982, IAU Symposium 97, 389.Google Scholar
Backer, D. C. and Sramek, R. A. (1987), personal communication.Google Scholar
Blandford, R. and Narayan, R. (1985), M.N.R.A.S. 213, 591.Google Scholar
Blandford, R., Narayan, R. and Romani, R. W. (1986) Ap. J. (Letters) 301, L53.CrossRefGoogle Scholar
Braun, R. (1987), personal communication.Google Scholar
Brown, R. L. and Johnson, K. J. (1983), Ap. J. (Letters) 268, L85.Google Scholar
Brown, R. L. and Lo, K. Y. (1982), Ap. J. 253, 108.Google Scholar
Coles, W. A., Frehlich, R. G., Rickett, B. J. and Codona, J. L. (1987), Ap. J. 315, 666.Google Scholar
Cordes, J. M., Pidwerbetsky, A. and Lovelace, R. V. E. (1986), Ap. J. 310, 737.Google Scholar
Davies, R. D., Walsh, D., and Booth, R. S. (1976), M.N.R.A.S. 177, 319.Google Scholar
Ekers, R. D., van Gorkom, J. H., Schwarz, U. J. and Goss, W. M. (1983), Astron. Astrophy. 122, 143.Google Scholar
Ekers, R. D., Zhao, J.-H. and Lo, K. Y. (1987), personal communication.Google Scholar
Geballe, T. R., Krisciunas, K., Lee, T. J., Gatley, I., Wade, R., Duncan, W. D., Garden, R., Becklin, E. E. (1984), Ap. J. 284, 118.CrossRefGoogle Scholar
Geballe, T. R., Wade, R., Krisciunas, K., Gatley, I., and Bird, M. C. (1987), Ap. J. 320, 562.Google Scholar
Goodman, J. and Narayan, R. (1985), M.N.R.A.S. 214, 519.Google Scholar
Goss, W. M. (1987), personal communication.Google Scholar
Hjellming, R. M. and Narayan, R. (1986), Ap. J. 310, 768.Google Scholar
Kellermann, K.I. and Pauliny-Toth, I. (1981), Ann. Rev. Astr. Ap. 19, 373.Google Scholar
Lacy, J. H., Townes, C. H., Geballe, T. R., Hollenbach, D. J. (1980), Ap. J. 241, 132.Google Scholar
Lo, K. Y. et al. (1975), Ap. J. (Letters) 202, L63 Google Scholar
Lo, K. Y., Backer, D. C., Ekers, R. D. Kellermann, K. I., Reid, M. and Moran, J. M. (1985), Nature 315, 124.Google Scholar
Lo, K. Y. (1987), in The Galactic Center AIP Conf. Proc. 155, ed. Backer, D. C., p. 30.Google Scholar
Rickett, B. J., Coles, W. A. and Bourgois, G. (1984), Astron. Astrophy. 134, 390.Google Scholar
Rickett, B. J. (1986), Ap. J. 307, 564.Google Scholar
Romani, R. W., Narayan, R. and Blandford, R. (1986), M.N.R.A.S. 220, 19.Google Scholar
Serabyn, E., Lacy, J. H. (1985), Ap. J. 293, 445.Google Scholar
van Gorkom, J. H., Schwarz, U. J., and Bregman, J. D. (1985) In The Milky Way Galaxy, IAU Symp. No 106 , ed. Van Woerden, H., Burton, W. B., Allen, R. J. Dordrecht: Reidel.Google Scholar
van Gorkom, J. H., Schwarz, U. J., and Bregman, J. D. (1988), In preparation.Google Scholar