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Title:
A Radio Outburst Nearly Coincident with the Large X-Ray Flare from Sagittarius A* on 2002 October 3
Authors:
Zhao, Jun-Hui; Herrnstein, R. M.; Bower, G. C.; Goss, W. M.; Liu, S. M.
Affiliation:
AA(Harvard-Smithsonian Center for Astrophysics, MS 78, 60 Garden Street, Cambridge, MA 02138; .), AB(Harvard-Smithsonian Center for Astrophysics, MS 78, 60 Garden Street, Cambridge, MA 02138; .; Department of Astronomy, Columbia University, Mail Code 5246, 550 West 120th Street, New York, NY 10027.), AC(Radio Astronomy Laboratory, University of California at Berkeley, 601 Campbell Hall, Berkeley, CA 94720.), AD(National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801.), AE(Center for Space Science and Astrophysics, Stanford University, Stanford, CA 94305-4060.)
Publication:
The Astrophysical Journal, Volume 603, Issue 2, pp. L85-L88. (ApJ Homepage)
Publication Date:
03/2004
Origin:
UCP
ApJ Keywords:
Accretion, Accretion Disks, Black Hole Physics, Galaxies: Active, Galaxy: Center, Radio Continuum: Galaxies
DOI:
10.1086/383128
Bibliographic Code:
2004ApJ...603L..85Z

Abstract

A large radio outburst from Sgr A* was observed during the Very Large Array weekly monitoring program at 2 cm, 1.3 cm, and 7 mm, nearly coincident with the brightest X-ray flare detected to date with the XMM-Newton X-ray observatory on 2002 October 3. The flux density of 1.9+/-0.2 Jy measured at 7 mm exceeds the mean value (1.00+/-0.01 Jy) by a factor of ~2, one of the two highest increases observed during the past 3 yr (2000 June-2003 October), while less significant increases in flux densities were observed at 1.3 and 2 cm. The radio observation started 13.5 hr after the onset of the X-ray flare (which had occurred over a 45 minute duration) and continued for 1.3 hr. During the observation, there was no significant (<3 σ) change in the radio flux densities at all three wavelengths, indicating that the radio outburst varied on a timescale of greater than 1 hr. A spectral index of α=2.4+0.3-0.6 (S~να) was derived for the outburst component, consistent with an optically thick nonthermal synchrotron source. These results suggest that energetic electrons responsible for the radio outburst might be produced via a process associated with the X-ray flare then transported to large radii, producing the observed radio outburst. The observation is the first evidence for a correlated variation in the radio and X-ray emissions from Sgr A*.
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