2005/03/31 by T. an, Tao An, W. M. Goss +10
Physics and Astronomy · #Absorption (acoustics) #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Flux (metallurgy) #Galactic Center #Galaxy #Giant Metrewave Radio Telescope #Millimeter #Optics #Physics #Pulsars and Gravitational Waves Research #Radio galaxy #Sagittarius A* #Stars #Telescope #Wavelength #astro-ph
paper · pdf · doi:10.1086/498687
15 pages, 4 figures, accepted by ApJ Letter
arxiv created 2005/10/12 · openalex publication_date 2005/11/03 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
We observed Sgr A* using the Very Large Array (VLA) and the Giant Metrewave Radio Telescope (GMRT) at multiple centimeter and millimeter wavelengths on 2003 June 17. The measured flux densities of Sgr A*, together with those obtained from the Submillimeter Array (SMA) and the Keck II 10 m telescope on the same date, are used to construct a simultaneous spectrum of Sgr A* from 90 cm to 3.8 μm. The simultaneous spectrum shows a spectral break at about 3.6 cm, a possible signature of synchrotron self-absorption of the strong radio outburst that occurred near epoch 2003 July 17. At 90 cm, the flux density of Sgr A* is 0.22 ± 0.06 Jy, suggesting a sharp decrease in flux density at wavelengths longer than 47 cm. The spectrum at long cm wavelengths appears to be consistent with free-free absorption by a screen of ionized gas with a cutoff ~100 cm. This cutoff wavelength appears to be three times longer than that of ~30 cm suggested by Davies, Walsh, & Booth based on observations in 1974 and 1975. Our analysis suggests that the flux densities of Sgr A* at wavelengths longer than 30 cm could be attenuated and modulated by stellar winds from massive stars close to Sgr A*.