Extreme Supernova Models for the Super-Luminous Transient Asassn-15lh

Abstract

The recent discovery of the unprecedentedly super-luminous transient ASASSN-15lh (or SN 2015L) with its UVbright secondary peak challenges all the power-input models that have been proposed for super-luminous supernovae. Here we examine some of the few viable interpretations of ASASSN-15lh in the context of a stellar explosion, involving combinations of one or more power inputs. We model the lightcurve of ASASSN-15lh with a hybrid model that includes contributions from magnetar spin-down energy and hydrogen-poor circumstellar interaction. We also investigate models of pure circumstellar interaction with a massive hydrogen-deficient shell and discuss the lack of interaction features in the observed spectra. We find that, as a supernova, ASASSN-15lh can be best modeled by the energetic core-collapse of an ∼40M e star interacting with a hydrogen-poor shell of ∼20M e . The circumstellar shell and progenitor mass are consistent with a rapidly rotating pulsational pairinstability supernova progenitor as required for strong interaction following the final supernova explosion. Additional energy injection by a magnetar with aninitial period of 1-2 ms and magnetic field of 0.1-1×10 14 G may supply the excess luminosity required to overcome the deficit in single-component models, but this requires more fine-tuning and extreme parameters for the magnetar, as well as the assumption of efficient conversion of magnetar energy into radiation. We thus favor a single-input model where the reverse shock formed in a strong SN ejecta-circumstellar matter interaction following a very powerful core-collapse SN explosion can supply the luminosity needed to reproduce the late-time UV-bright plateau.

X-Rays from the Location of the Double-humped Transient ASASSN-15lh

“…Figure 4 shows the presence of pronounced temporal variability across the UVOT bands, and it is more pronounced at UV wavelengths as first noticed by Brown et al (2016b). The short variability timescale  Dt 5 days at ∼150 days since first light argues against the interpretation of the SN shock interaction with the surroundings as the main source of energy powering the rebrightening (Chatzopoulos et al 2016), unless the circumstellar medium (CSM) is clumpy and with structure on short length scales. For a typical SN shock velocityṽ 0.2 sh c (e.g., Margutti et al 2014b, their Figure 2) we do not expect significant temporal variability on D < t 30 days att 150 days, contrary to what we observe in ASASSN-15lh.…”

Results from a Systematic Survey of X-Ray Emission from Hydrogen-poor Superluminous SNe

“…Given the peculiar nature of ASASSN-15lh (Dai et al 2015;Metzger et al 2015;Bersten et al 2016;Chatzopoulos et al 2016;Dong et al 2016;Godoy-Rivera et al 2017;Kozyreva et al 2016;Leloudas et al 2016;Sukhbold & Woosley 2016;van Putten & Della Valle 2017;Margutti et al 2017a), this transient is not part of the sample of bona fide SLSNe-I analyzed here. However, we discuss and compare the X-ray properties of ASASSN-15lh in the context of SLSNe-I in Section 4, 5.1 and 5.2.…”

Analyzing the Largest Spectroscopic Data Set of Hydrogen-poor Super-luminous Supernovae

“…Recently, hybrid models have invoked several of these mechanisms for the same object to explain the peculiar light curves (e.g., PTF12dam by Tolstov et al 2016, iPTF13ehe by Wang et al 2016 by Chatzopoulos et al 2016). Based on current observations of SLSNe, the PISN origin has been disfavored for most of the SLSNe I (except for SN 2007bi; Gal-Yam et al 2009) for a number of reasons.…”