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Observations of the small diameter radio source in the galactic centre have been made at o·408, 0·96 and 1 ·66 GHz. These measurements show a low-frequency cut-off in the spectrum which is considered to be due to free–free absorption in the Sgr A West H II region. The nuclear source has a diameter of |1^4| arc at 1 GHz. The observed change of diameter with wavelength indicates that the observed diameters are a result of interstellar scattering. No significant intensity variation has been detected over a period of several years. On the basis of available data the nuclear source is considered to be located at the nucleus of the Galaxy and is either the early stages of a supernova remnant or a pulsar.
Davies et al. (Mon,) studied this question.