Abstract
We present the first maximum-light ultraviolet (UV) through near-infrared (NIR) Type Ia supernova (SN Ia) spectrum. This spectrum of SN 2011iv was obtained nearly simultaneously by the Hubble Space Telescope at UV/optical wavelengths and the Magellan Baade telescope at NIR wavelengths. These data provide the opportunity to examine the entire maximum-light SN Ia spectral-energy distribution. Since the UV region of a SN Ia spectrum is extremely sensitive to the composition of the outer layers of the explosion, which are transparent at longer wavelengths, this unprecedented spectrum can provide strong constraints on the composition of the SN ejecta, and similarly the SN explosion and progenitor system. SN 2011iv is spectroscopically normal, but has a relatively fast decline (Delta m_15 (B) = 1.69 +/- 0.05 mag). We compare SN 2011iv to other SNe Ia with UV spectra near maximum light and examine trends between UV spectral properties, light-curve shape, and ejecta velocity. We tentatively find that SNe with similar light-curve shapes but different ejecta velocities have similar UV spectra, while those with similar ejecta velocities but different light-curve shapes have very different UV spectra. Through a comparison with explosion models, we find that both a solar-metallicity W7 and a zero-metallicity delayed-detonation model provide a reasonable fit to the spectrum of SN 2011iv from the UV to the NIR.
Highlights
Type Ia supernovae (SNe Ia) are the energetic end of C/O white dwarfs in binary systems that reach temperatures and densities high enough to cause a runaway chain of nuclear reactions
In Cycle 17, 30 SNe Ia were observed at a single epoch by Hubble Space Telescope (HST) (GO-11721; PI: Ellis); these spectra did not probe below 2900 Å (Cooke et al 2011)
Fitting the B and V light curves (Figure 1) with a third-order polynomial function, we estimate that SN 2011iv reached maximum light in the B band on 2,455,906.0 ± 0.3 JD and peaked at B = 12.53 ± 0.03 mag and V = 12.51 ± 0.03 mag
Summary
Type Ia supernovae (SNe Ia) are the energetic end of C/O white dwarfs in binary systems that reach temperatures and densities high enough to cause a runaway chain of nuclear reactions (for a review, see Hillebrandt & Niemeyer 2000). SNe Ia have remarkably uniform luminosity (σ ≈ 0.16 mag; e.g., Hicken et al 2009), after correcting for light-curve shape and color. This relationship extends to the U band, but with larger scatter (Jha et al 2006). In Cycle 17, 30 SNe Ia were observed at a single epoch by HST (GO-11721; PI: Ellis); these spectra did not probe below 2900 Å (Cooke et al 2011) It has been 20 years since the last high-S/N true-UV maximum-light SN Ia spectrum has been observed and published. In this Letter, we focus on this first UV–optical–NIR (UVOIR) spectrum spanning 0.16–2.5 μm
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