Early Near-Infrared Observations of SN 1993J

Photometric observations in the near-infrared atmospheric windows from 1.25 to 3.7 μm and spectrographic observations from 1.2 to 2.4 μm are presented of supernova SN 1993J for 250 days after the outburst. After an initial rise to a secondary maximum the infrared observations show an exponential drop much like the visual observations. At day 130 after the outburst, however, the 3.7 μm data show an excess, which we take as a signature of dust emission. Broadband spectral energy distributions (SEDs) were derived combining published visual photometry and the infrared photometry. The early SEDs during the supernova rise to its secondary maximum could be fitted with blackbodies, but during the exponential decrease the SEDs were too narrow to be fitted by a blackbody energy distribution. The low-resolution spectra were initially featureless, but beyond about day 30 after the outburst, when SN 1993J was in exponential decline, the spectra were dominated by line emission, probably by hydrogen, helium, and iron lines.