2017ApJ...850..111N

SN 2015J was discovered on 2015 April 27th and is classified as an SN IIn. At first, it appeared to be an orphan SN candidate, i.e., without any clear identification of its host galaxy. Here, we present an analysis of the observations carried out by the VLT 8 m class telescope with the FORS2 camera in the R band and the Magellan telescope (6.5 m) equipped with the IMACS Short-Camera (V and I filters) and the FourStar camera (Ks filter). We show that SN 2015J resides in what appears to be a very compact galaxy, establishing a relation between the SN event and its natural host. We also present and discuss archival and new X-ray data centered on SN 2015J. At the time of the supernova explosion, Swift/XRT observations were made and a weak X-ray source was detected at the location of SN 2015J. Almost one year later, the same source was unambiguously identified during serendipitous observations by Swift/XRT and XMM-Newton, clearly showing an enhancement of the 0.3-10 keV band flux by a factor ≃30 with respect to the initial state. Swift/XRT observations show that the source is still active in the X-rays at a level of ≃0.05 counts s^–1. The unabsorbed X-ray luminosity derived from the XMM-Newton slew and SWIFT observations, L_x≃5×10⁴¹ erg s^–1, places SN 2015J among the brightest young supernovae in X-rays.