The central region of the Galaxy has been observed at 580, 620 and 1010 MHz with the Giant Metrewave Radio Telescope (GMRT). We detect emission from Sgr A*, the compact object at the dynamical centre of the Galaxy, and estimate its flux density at 620 MHz to be 0.5 +/- 0.1 Jy. This is the first detection of Sgr A* below 1 GHz, which along with a possible detection at 330 MHz provides its spectrum below 1 GHz. Comparison of the 620-MHz map with maps made at other frequencies indicates that most parts of the Sgr A West H II region have optical depth ~2. However, Sgr A*, which is seen in the same region in projection, shows a slightly inverted spectral index between 1010 and 620 MHz. This is consistent with its high-frequency spectral index, and indicates that Sgr A* is located in front of the Sgr A West complex, and rules out any low-frequency turnover around 1 GHz, as suggested by Davies, Walsh & Booth.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2004
- techniques: interferometric;
- H II regions;
- Galaxy: centre;
- 5 pages, 4 figures, accepted for publication in MNRAS Letters