Open AccessSgr A* at low radio frequencies: Giant Metrewave Radio Telescope observations
Author(s) -
Roy Subhashis,
Pramesh Rao A.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07693.x
Subject(s) - giant metrewave radio telescope , physics , astrophysics , astronomy , radio telescope , radio astronomy , radio frequency , radio galaxy , galaxy , telecommunications , computer science
ABSTARCT 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.