The intrinsic colour dispersion in Type Ia supernovae

¹ Department of Physics, Stockholm University, SCFAB, 106 91 Stockholm, Sweden
² Department of Physics & Astronomy, Vanderbilt University, USA
³ Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA

Corresponding author: S. Nobili, serena@physto.se

Received: 14 February 2003
Accepted: 6 April 2003

Abstract

The properties of low-redshift Type Ia supernovae are investigated using published multi-band optical broadband data from the Calan/Tololo and CfA surveys. The average time evolution of , , , and , the intrinsic dispersion and time correlations are studied. This information is required to deduce the extinction of such explosions from the measured colours. We find that extinction corrections on individual SNe based on their colours up to 40 days past the -band lightcurve maximum are generaly limited to , due to intrinsic variations, as far as it can be conservatively deduced with the current sample of data. However, we find that the colour, especially at late times, is consistent with a negligible intrinsic spread, and may be the most accurate estimator for extinction.