On 2011 August 11, INTEGRAL discovered the hard X-ray source IGR J17361-4441 near the centre of the globular cluster NGC 6388. Follow up observations with Chandra showed the position of the transient was inconsistent with the cluster dynamical centre, and thus not related to its possible intermediate mass black hole. The source showed a peculiar hard spectrum (Γ ≈ 0.8) and no evidence of QPOs, pulsations, type-I bursts, or radio emission. Based on its peak luminosity, IGR J17361-4441 was classified as a very faint X-ray transient, and most likely a low-mass X-ray binary. We re-analysed 200 days of Swift/XRT observations, covering the whole outburst of IGR J17361-4441 and find a t −5/3 trend evident in the light curve, and a thermal emission component that does not evolve significantly with time. We investigate whether this source could be a tidal disruption event, and for certain assumptions find an accretion efficiency ǫ ≈ 3.5 × 10 −4 (M Ch /M ) consistent with a massive white dwarf, and a disrupted minor body mass M mb ≈ 1.9 × 10 27 (M/M Ch ) g in the terrestrial-icy planet regime. These numbers yield an inner disc temperature of the order kT in ≈ 0.04 keV, consistent with the blackbody temperature of kT in ≈ 0.08 keV estimated by spectral fitting. Although the density of white dwarfs and the number of free-floating planets are uncertain, we estimate the rate of planetary tidal disruptions in NGC 6388 to be in the range 3 × 10 −6 to 3 × 10 −4 yr −1 . Averaged over the Milky Way globular clusters, the upper limit value corresponds to 0.05 yr −1 , consistent with the observation of a single event by INTEGRAL and Swift.

We present a sample of X-ray selected candidate black holes in 51 low mass galaxies with z ≤ 0.055 and mass up to 10 10 M ⊙ obtained by cross-correlating the NASA-SLOAN Atlas with the 3XMM catalogue. We have also searched in the available catalogues for radio counterparts of the black hole candidates and find that 19 of the previously selected sources have also a radio counterpart. Our results show that about 37% of the galaxies of our sample host an X-ray source (associated to 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 results to be in the range 10 4 − 2 × 10 8 M ⊙ (with median value of ≃ 3 × 10 7 M ⊙ and eight candidates having mass below 10 7 M ⊙ ). 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 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.

In gravitational microlensing, binary systems may act as lenses or sources. Identifying lens binarity is generally easy especially in events characterized by caustic crossing since the resulting light curve exhibits strong deviations from smooth single-lensing light curve. On the contrary, light curves with minor deviations from a Paczyński behaviour do not allow one to identify the source binarity. A consequence of the 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 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.