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In recent years, thanks to the continuous surveys performed by INTEGRAL and Swift satellites, our knowledge of the hard X-ray/soft gamma-ray sky has greatly improved. As a result it is now populated with about 2000 sources, both Galactic and extra-galactic, mainly discovered by IBIS and BAT instruments. Many different follow-up campaigns have been successfully performed by using a multi-wavelength approach, shedding light on the nature of a number of these new hard X-ray sources. However, a fraction are still of a unidentified nature. This is mainly due to the lack of lower energy observations, which usually deliver a better constrained position for the sources, and the unavailability of the key observational properties, needed to obtain a proper physical characterization. Here we report on the classification of two poorly studied Galactic X-ray transients IGR J20155+3827 and Swift J1713.4-4219, for which the combination of new and/or archival X-ray and Optical/NIR observations have allowed us to pinpoint their nature. In particular, thanks to XMMNewton archival data together with new optical spectroscopic and archival Optical/NIR photometric observations, we have been able to classify IGR J20155+3827 as a distant HMXB. The new INTEGRAL and Swift data collected during the 2019 X-ray outburst of Swift J1713.4-4219, in combination with the archival optical/NIR observations, suggest a LMXB classification for this source.
We present simultaneous, multi-wavelength observations of the Small Magellanic Cloud Be/XRB IGR J01217-7257 (=SXP 2.16) during outbursts in 2014, 2015 and 2016. We also present the results of RXTE observations of the Small Magellanic Cloud during whi
We present the results obtained from detailed spectral and timing studies of extra-galactic black hole X-ray binaries LMC~X--1 and LMC~X--3, using simultaneous observations with {it Nuclear Spectroscopic Telescope Array (NuSTAR)} and {it Neil Gehrels
We present late-time multi-wavelength observations of Swift J1644+57, suggested to be a relativistic tidal disruption flare (TDF). Our observations extend to >4 years from discovery, and show that 1.4 years after outburst the relativistic jet switche
We summarize the results of our long-running campaign to help understand the nature of high-mass X-ray binaries (HMXBs), emphasizing recent Suzaku observations of IGR J16207-5129 and IGR J17391-3021. Thanks to the expanding ranks of HMXBs in our Gala
In this paper we report on a long multi-wavelength observational campaign of the supergiant fast X-ray transient prototype IGR J17544-2619. A 150 ks-long observation was carried out simultaneously with XMM-Newton and NuSTAR, catching the source in an