A RAPID DECLINE IN THE OPTICAL-EMISSION FROM SN-1957D IN M83

As part of a search for the supernova remnants in M83, we have obtained new interference filter images of the site of SN 1957D and new spectra of the young supernova remnant (SNR) itself. Images were obtained in the light of H-alpha, [O III], [S II], and several continuum bands using the prime focus CCD camera on the CTIO 4 m telescope. An inspection of the images shows that the flux from the SNR, as observed through the [O III] filter, has decreased by at least a factor of 5 compared with observations made at Las Campanas 4 yr earlier. There is no indication of a change in the emission from the SNR in any other filter. Spectroscopic observations conducted at the position of the SN yield an [O III] flux of 1.8 x 10(-15) ergs cm-2 s-1 in 1991 April, down by a factor of 3 from measurements with the same instrument 2 yr earlier.