Anomalous extinction behaviour towards the Type Ia SN 2003cg

Abstract

We present optical and near-infrared photometry and spectroscopy of the Type la SN 2003cg, which exploded in the nearby galaxy NGC 3169. The observations cover a period between -8.5 and +414d post-maximum. SN 2003cg is a normal but highly reddened Type Ia event. Its B magnitude at maximum B max = 15.94 ± 0.04 and Δm15(B)obs = 1.12 ± 0.04 [Δm15(5)intrinsic = 1.25 ± 0.05]. Allowing RV to become a free parameter within the Cardelli et al. extinction law, simultaneous matches to a range of colour curves of normal SNe la yielded E(B - V) = 1.33 ± 0.11, and RV = 1.80 ± 0.19. While the value obtained for RV is small, such values have been invoked in the past, and may imply a grain size which is small compared with the average value for the local interstellar medium. © 2006 RAS.