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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 with respect to the initial state. Swift/XRT observations show that the source is still active in the X-rays at a level of counts s−1. The unabsorbed X-ray luminosity derived from the XMM-Newton slew and SWIFT observations, erg s−1, places SN 2015J among the brightest young supernovae in X-rays. [ABSTRACT FROM AUTHOR]

We present a sample of X-ray-selected candidate black holes in 51 low-mass galaxies with z ≤ 0.055 and masses up to 1010M⊙ obtained by cross-correlating the NASA-SLOAN Atlas with the 3XMM catalog. We have also searched in the available catalogs for radio counterparts of the black hole candidates and find that 19 of the previously selected sources also have a radio counterpart. Our results show that about 37% of the galaxies of our sample host an X-ray source (associated with a radio counterpart) spatially coincident with the galaxy center, in agreement with other recent works. For these nuclear sources, the X-ray/radio fundamental plane relation allows one to estimate the mass of the (central) candidate black holes, which are in the range of 104–2 × 108M⊙ (with a median value of ≃3 × 107M⊙ and eight candidates having masses below 107M⊙). This result, while suggesting that X-ray emitting black holes in low-mass galaxies may have had a key role in the evolution of such systems, makes it even more urgent to explain how such massive objects formed in galaxies. Of course, dedicated follow-up observations both in the X-ray and radio bands, as well as in the optical, are necessary in order to confirm our results. [ABSTRACT FROM AUTHOR]

In gravitational microlensing, binary systems may act as lenses or sources. Identifying lens binarity is generally easy, in particular in events characterized by caustic crossing since the resulting light curve exhibits strong deviations from a smooth single-lensing light curve. In contrast, light curves with minor deviations from a Paczyński behavior do not allow one to identify the source binarity. A consequence of gravitational microlensing is the shift of the position of the multiple image centroid with respect to the source star location — the so-called astrometric microlensing signal. When the astrometric signal is considered, the presence of a binary source manifests with a path that largely differs from that expected for single source events. Here, we investigate the astrometric signatures of binary sources taking into account their orbital motion and the parallax effect due to the Earth’s motion, which turn out not to be negligible in most cases. We also show that considering the above-mentioned effects is important in the analysis of astrometric data in order to correctly estimate the lens-event parameters. [ABSTRACT FROM AUTHOR]