Thermonuclear Supernovae: Probing Magnetic Fields by Late-Time IR Line Profiles

Abstract

We study the imprint of magnetic fields B on late-time IR line profiles and light curves of Type Ia Supernovae. As a benchmark, we use the explosion of a Chandrasekhar mass M_{Ch White Dwarf (WD) and, specifically, a delayed detonation model. We assume WDs with initial magnetic surface fields between 1 and 1E9G. We discuss large-scale dipole and small-scale magnetic fields. We find that the [Fe II] line at 1.644 mu can be used to analyze the overall chemical and density structure of the exploding WD up to day 200 without considering B. Subsequently, positron transport and magnetic field effects become important. By day 500, the profile becomes sensitive to the morphology of B and directional dependent for dipole fields. Small or no directional dependence of the spectra is found for small-scale B. After about 200 days, persistent broad-line, flat-topped or stumpy profiles require high density burning which is the signature of a WD close to M_Ch. Narrow peaked profiles are a signature of chemical mixing or sub-MCh WDs. Good time coverage is required to separate the effects of optical depth, the size and morphology of B, and the aspect angle of the observer. The spectra require a resolution of about 500 km/sec and a signal to noise ratio of about 20%. Line blending effect are demonstrated at the example of equally prominent features at about 1.5 and 1.8 mu. For some SNeIa, spectra beyond day 300 have been observed which lend support for M_Ch mass explosions in at least some cases, and require magnetic fields equal to or in excess of 1E6G. We briefly discuss the effects of the size and morphology of B on light curves and the limitations in light of the diversity of SNeIa. We argue that line profiles are a more direct measurement of B.