The absolute infrared magnitudes of type Ia supernovae

The absolute luminosities and homogeneity of early-time infrared (IR) Light curves of type Ia supernovae are examined. Eight supernovae are considered . These are selected to have accurately known epochs of maximum blue light as well as having reliable distance estimates and/or good light curve cover age. Two approaches to extinction correction are considered. Owing to the l ow extinction in the IR, the differences in the corrections via the two met hods are small. Absolute magnitude light curves in the J, H and K bands are derived. Six of the events, including five established 'branch-normal' sup ernovae, show similar coeval magnitudes. Two of these, supernovae (SNe) 198 9B and 1998bu, were observed near maximum infrared light. This occurs about 5 d before maximum blue light. Absolute peak magnitudes of about - 19.0, - 18.7 and - 18.8 in J, H and K respectively were obtained. The two spectros copically peculiar supernovae in the sample, SNe 1986G and 1991T, also show atypical IR behaviour. The light curves of the six similar supernovae can be represented fairly consistently with a single light curve in each of the three bands. In all three IR bands the dispersion in absolute magnitude is about 0.15 mag, and this can be accounted for within the uncertainties of the individual light curves, No significant variation of absolute IR magnit ude with B-band light curve decline rate, Delta m(15)(B), is seen over the range 0.87 < Delta m(15)(B) < 1.31. However, the data are insufficient to a llow us to decide whether or not the decline rate relation is weaker in the IR than in the optical region. IR light curves of type Ia supernovae shoul d eventually provide cosmological distance estimates that are of equal, or even superior, quality to those obtained in optical studies.