We present a spectrum of Sgr A* observed simultaneously on June 17 , 2003 at wavelengths from 90 to 0.7 cm with the VLA .
In the spectrum , we also include the measurements of Sgr A* observed on the same day with the GMRT at 49 cm , the SMA at 0.89 mm and the Keck II at 3.8 \mu m. The spectrum at the centimeter wavelengths suggests the presence of a break wavelength at \lambda _ { b } \sim 3.8 cm ( 8 GHz ) .
The spectral index is \alpha = 0.43 \pm 0.03 ( { S \propto \nu ^ { \alpha } } ) at 3.8 cm and shorter wavelengths .
The spectrum between \lambda = 3.8 cm and \lambda = 49 cm can be described by a power law with spectral index of \alpha = 0.10 \pm 0.03 .
We detected Sgr A* with 0.22 \pm 0.06 Jy at 90 cm , suggesting a sharp decrease in flux density at the wavelengths longer than 49 cm .
The best fit to the spectrum at the wavelengths longer than \lambda _ { b } appears to be consistent with free-free absorption by a screen of ionized gas with a turnover wavelength at \nu ( \tau _ { ff } = 1 ) \sim 100 cm ( 300 MHz ) .
This turnover wavelength appears to be three times longer than that of 30 cm ( 1 GHz ) as suggested by Davies et al .
( [ 1976 ] ) based on the observations in 1994 and 1995 .
Our analysis suggests that stellar winds from the massive stars near Sgr A* could modulate the flux density at the wavelengths longer than 30 cm ( or frequencies below 1 GHz ) .