A Radio Outburst Nearly Coincident with the Large X-Ray Flare from Sagittarius A* on 2002 October 3

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 ( S ∝ ν α ) 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*.