Ultraviolet Spectroscopy of Supernovae: The First Two Years of Swift Observations

TL;DR

This paper presents the first two years of ultraviolet spectroscopic observations of supernovae using Swift UVOT, revealing diversity in Type Ia UV emission and homogeneity in Type II, with implications for early supernova studies.

Contribution

It provides the first comprehensive UV spectral dataset of supernovae from Swift UVOT, highlighting spectral diversity and the need for longer exposures to enhance understanding.

Findings

Diversity observed in Type Ia supernova UV spectra.

Homogeneity found in Type II Plateau supernova UV spectra.

Interaction signatures detected in SN 2006jc UV spectrum.

Abstract

We present the entire sample of ultraviolet (UV) spectra of supernovae (SNe) obtained with the Ultraviolet/Optical Telescope (UVOT) on board the Swift satellite during the first 2 years of observations (2005/2006). A total of 29 UV-grism and 22 V-grism spectra of 9 supernovae (SNe) have been collected, of which 6 are thermonuclear (type Ia) and 3 core collapse (type Ibc/II) SNe. All the spectra have been obtained during the photospheric phase. After a comparison of the spectra of our sample with those in the literature (SNe 1992A, 1990N and 1999em), we confirm some degree of diversity in the UV emission of Type Ia SNe and a greater homogeneity in the Type II Plateau SN sample. Signatures of interaction between the ejecta and the circumstellar environment have been found in the UV spectrum of SN 2006jc, the only SN Type Ib/c for which UVOT grism data are available. Currently, Swift UVOT is the best suited instrument for early SN studies in the UV due to its fast response and flexible scheduling capabilities. However, in order to increase the quality of the data and significantly improve our understanding of the UV properties of SNe and to fully maximize the scientific potential of UVOT grism observations, a larger investment in observing time and longer exposures are needed.