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We report the results of radio flux-monitoring and high resolutionobservations at 3.6 cm with the VLA, of the central condensation in G10.0-0.3,the radio nebula surrounding the soft gamma ray repeater (SGR) 1806-20. Thequiescent X-ray source AX1805.7-2025 is coincident with the radio coresuggesting that G10.0-0.3 is a plerionic supernova remnant. The monitoringexperiment was performed in 10 epochs spread over five months, starting justbefore the latest reactivation of SGR 1806-20 in gamma-rays. There is noapparent increase in the radio flux density from the central region ofG10.0-0.3 on timescales of days to months following the gamma-ray bursts. At aresolution of 1 arcsec the peak region of G10.0-0.3 is seen to consist of acompact source with diffuse, one-sided emission, reminiscent of core-jetgeometry seen in AGNs and some accreting Galactic binaries. By analogy withthese latter sources, we argue that the SGR 1806-20 is coincident with the corecomponent. If so, this is the first arcsecond localization of a high energytransient. The lack of radio variability and the low brightness temperature ofthe central component distinguish SGR 1806-20 from other accreting binaries.The structure of the high resolution radio image also does not particularlyresemble that seen in the vicinity of young pulsars. Thus there is nocompelling observational evidence for either of the two models discussed forSGRs, the pulsar model or the accreting binary model.Comment: Requests for figures and tables from authors, 14 pages AAS format.  Requests to gv@astro.caltech.ed

Radio monitoring and high-resolution imaging of the soft gamma-ray repeater 1806-20