Superluminous supernovae from PESSTO

Abstract

We present optical spectra and light curves for three hydrogen-poor\nsuper-luminous supernovae followed by the Public ESO Spectroscopic Survey of\nTransient Objects (PESSTO). Time series spectroscopy from a few days after\nmaximum light to 100 days later shows them to be fairly typical of this class,\nwith spectra dominated by Ca II, Mg II, Fe II and Si II, which evolve slowly\nover most of the post-peak photospheric phase. We determine bolometric light\ncurves and apply simple fitting tools, based on the diffusion of energy input\nby magnetar spin-down, 56Ni decay, and collision of the ejecta with an opaque\ncircumstellar shell. We investigate how the heterogeneous light curves of our\nsample (combined with others from the literature) can help to constrain the\npossible mechanisms behind these events. We have followed these events to\nbeyond 100-200 days after peak, to disentangle host galaxy light from fading\nsupernova flux and to differentiate between the models, which predict diverse\nbehaviour at this phase. Models powered by radioactivity require unrealistic\nparameters to reproduce the observed light curves, as found by previous\nstudies. Both magnetar heating and circumstellar interaction still appear to be\nviable candidates. A large diversity is emerging in observed tail-phase\nluminosities, with magnetar models failing in some cases to predict the rapid\ndrop in flux. This would suggest either that magnetars are not responsible, or\nthat the X-ray flux from the magnetar wind is not fully trapped. The light\ncurve of one object shows a distinct re-brightening at around 100d after\nmaximum light. We argue that this could result either from multiple shells of\ncircumstellar material, or from a magnetar ionisation front breaking out of the\nejecta.\n