paper

Detection of Broad H Emission Lines in the Late-time Spectra of a Hydrogen-poor Superluminous Supernova

arXiv:1508.04420 · doi:10.1088/0004-637X/814/2/108

Abstract

iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z=0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises within (83-148)days (rest-frame) to reach a peak bolometric luminosity of 1.3xerg/s, then decays very slowly at 0.015mag. per day. The measured ejecta velocity is 13000km/s. The inferred explosion characteristics, such as the ejecta mass (67-220), the total radiative and kinetic energy ( & 2xerg respectively), is typical of a slow-evolving H-poor SLSN event. However, the late-time spectrum taken at +251days reveals a Balmer Halpha emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ~4500km/s and has a ~300km/s blue-ward shift relative to the narrow component. We interpret this broad H emission with luminosity of 2\,erg\,s as resulting from the interaction between the supernova ejecta and a discrete H-rich shell, located at a distance of \,cm from the explosion site. This ejecta-CSM interaction causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock ionized CSM shell implies that its Thomson scattering optical depth is likely <1, thus setting upper limits on the CSM mass <30 and the volume number density <4x. Of the existing models, a Pulsational Pair Instability Supernova model can naturally explain the observed 30 H-shell, ejected from a progenitor star with an initial mass of (95-150) about 40 years ago. We estimate that at least 15\%\ of all SLSNe-I may have late-time Balmer emission lines.

arXiv commentApJ accepted. All comments are welcome

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