Near-Ultraviolet Properties of a Large Sample of Type Ia Supernovae as Observed with the Swift UVOT

TL;DR

This study provides the most comprehensive UV and optical photometry of 26 Type Ia supernovae, revealing subclass differences and temporal characteristics of UV emission, which are crucial for understanding supernova diversity and evolution.

Contribution

It offers the first extensive UV dataset of SNe Ia, analyzing color evolution and UV light curve features across subclasses, enhancing understanding of supernova diversity.

Findings

Normal SNe Ia show high UV homogeneity, unlike subluminous and SN 2002cx-like groups.

UV light curves peak a few days before B-band, with early peaks in SN 2002cx-like objects.

UV emission characteristics vary significantly between subclasses, especially in the bluer filters.

Abstract

We present ultraviolet (UV) and optical photometry of 26 Type Ia supernovae (SNe~Ia) observed from March 2005 to March 2008 with the NASA {\it Swift} Ultraviolet and Optical Telescope (UVOT). The dataset consists of 2133 individual observations, making it by far the most complete study of the UV emission from SNe~Ia to date. Grouping the SNe into three subclasses as derived from optical observations, we investigate the evolution of the colors of these SNe, finding a high degree of homogeneity within the normal subclass, but dramatic differences between that group and the subluminous and SN 2002cx-like groups. For the normal events, the redder UV filters on UVOT ($u$, $uvw1$) show more homogeneity than do the bluer UV filters ($uvm2$, $uvw2$). Searching for purely UV characteristics to determine existing optically based groupings, we find the peak width to be a poor discriminant, but we do see a variation in the time delay between peak emission and the late, flat phase of the light curves. The UV light curves peak a few days before the $B$ band for most subclasses (as was previously reported by Jha et al. 2006a), although the SN 2002cx-like objects peak at a very early epoch in the UV. That group also features the bluest emission observed among SNe~Ia. As the observational campaign is ongoing, we discuss the critical times to observe, as determined by this study, in order to maximize the scientific output of future observations.