Diversity in extinction laws of Type Ia supernovae measured between 0.2 and 2 mu m

Amanullah, R.; Johansson, J.; Goobar, A.; Ferretti, R.; Papadogiannakis, S.; Petrushevska, T.; Brown, P. J.; Cao, Y.; Contreras, C.; Dahle, H.; Elias-Rosa, N.; Fynbo, J. P. U.; Gorosabel, J.; Guaita, L.; Hangard, L.; Howell, D. A.; Hsiao, E. Y.; Kankare, E.; Kasliwal, M.; Leloudas, G.; Lundqvist, P.; Mattila, S.; Nugent, P.; Phillips, M. M.; Sandberg, A.; Stanishev, V.; Sullivan, M.; Taddia, F.; Ostlin, G.; Asadi, S.; Herrero-Illana, R.; Jensen, J. J.; Karhunen, K.; Lazarevic, S.; Varenius, E.; Santos, P.; Sridhar, S. Seethapuram; Wallstrom, S. H. J.; Wiegert, J.
2015
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
DOI
10.1093/mnras/stv1505
We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2-2 mu m. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B - V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction R-V. In particular, we note that for the two SNe with E(B - V) greater than or similar to 1 mag, for which the colour excess is dominated by dust extinction, we find R-V = 1.4 +/- 0.1 and R-V = 2.8 +/- 0.1. Adding UV photometry reduces the uncertainty of fitted R-V by similar to 50 per cent allowing us to also measure R-V of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe.