Unveiling the true nature of the remarkable transient ASASSN-15lh

We propose deep Xray observations of ASASSN15lh at t>500 days to unveil itsnature, as part of our multiwavelength followup. ASASSN15lh has been interpreted as either (i) the most luminous stellar explosion, or (ii) a stellartidal disruption by the most massive, spinning black hole to date. In eithercase the observed properties of ASASSN15lh are unprecedented, with profoundimplications to our understanding of stellar explosions (case i) or stronggravity regimes around supermassive spinning BHs (case ii). The two scenarioshave markedly different predictions of the associated Xray emission and itsevolution at late times. Continued monitoring of the Xray source that weuncovered at its location thus holds the keys to unveiling the true nature of this unique transient. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]