Sgr A* at low radio frequencies: GMRT observations

Details Sgr A* at low radio frequencies: GMRT observations Sgr A* at low radio frequencies: GMRT observations

2004-02-02

arxiv.org/abs/astro-ph/0402052v1

Mon.Not.Roy.Astron.Soc. 349 (2004) L25

Astronomy and Astrophysics

Astrophysics

5 pages, 4 figures, accepted for publication in MNRAS Letters

Scientific paper

10.1111/j.1365-2966.2004.07693.x

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 (Roy & Rao 2002, 2003), which along with a possible detection at 330 MHz (Nord et al. 2004) 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 HII 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 MHz 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 et al. (1976).

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