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For refcode 1989ApJ...341..883S:
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1989ApJ...341..883S RADIO EMISSION FROM SUPERNOVA SN 1986J IN NGC 891 S. SUKUMAR AND R. J. ALLEN Department of Astronomy, University of Illinois Received 1988 June 20; accepted 1988 December 2 ABSTRACT We report radio detection at 90 cm of supernova SN 1986J in the edge-on galaxy NGC 891, and several prediscovery radio observations of the same object at 20 cm and 6 cm. These observations have been made over the past few years with the Westerbork Synthesis Radio Telescope and the Very Large Array. In approximately 1984, a discrete radio continuum source appeared above the extended radio disk emission from the galaxy NGC 891 at a position about 1' southeast of the nucleus. The flux density at 20 m increased from 7.5 to 11.7 mJy between 1984 August and 1985 January. Later, during 1987 September to 1988 March, the flux density at 90 cm was also observed to increase from ~ 9 to 14 mJy. On the other hand at 6 cm the flux density of this discrete source has been decreasing through mid-1988, after reaching a peak of more than 128 mJy at some time between mid-1984 and mid-1986. We compare these results with models of radio supernova. The radio characteristics are indicative of Type II, and free-free absorption by thermal electrons in the emitting region as well as in an external medium could be important. The radio spectral index between 6 and 20 cm varied from 1.5 to 0.4 over a period of two years (1984-1986), suggesting free-free absorption in a hot, optically thick thermal region surrounding the supernova which is slowly becoming optically thin at low frequencies. This circumstellar interaction model adequately fits the 6 cm radio data, but the fit at 90 cm is only marginally acceptable and at 20 cm the model does not fit the data well at all. A unique feature of SN 1986J is its high radio luminosity. It has been suggested that the precursor was an extremely massive star and that the surrounding medium was unusually dense. In a few years, the supernova could be as bright as 350 mJy at 90 cm and may be a prominent feature in the radio morphology of NGC 891 for several years thereafter. Subject headings: galaxies: individual (NGC 891) - interferometry - radio sources: identifications - stars: individual (SN 1986J) - stars: supernovae
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