SGUERA, VITOVITOSGUERASIDOLI, LaraLaraSIDOLIBird, A. J.A. J.BirdBAZZANO, ANGELAANGELABAZZANO2020-03-312020-03-3120150035-8711http://hdl.handle.net/20.500.12386/23747We thank an anonymous referee for useful comments which improved the quality of the paper.We report on a broad-band X-ray study (0.5-250 keV) of the Supergiant Fast X-ray Transient IGR J18483-0311 using archival INTEGRAL data and a new targeted XMM-Newton observation. Our INTEGRAL investigation discovered for the first time an unusually long X-ray activity (3-60 keV) which continuously lasted for at least ̃11 d, i.e. a significant fraction (̃60 per cent) of the entire orbital period, and spanned orbital phases corresponding to both periastron and apastron passages. This prolongated X-ray activity is at odds with the much shorter durations marking outbursts from classical SFXTs especially above 20 keV, as such it represents a departure from their nominal behaviour and it adds a further extreme characteristic to the already extreme SFXT IGR J18483-0311. Our IBIS/ISGRI high energy investigation (100-250 keV) of archival outbursts activity from the source showed that the recently reported hint of a possible hard X-ray tail is not real and it is likely due to noisy background. The new XMM-Newton targeted observation did not detect any sign of strong X-ray outburst activity from the source despite being performed close to its periastron passage, on the contrary IGR J18483-0311 was caught during the common intermediate X-ray state with a low-luminosity value of ̃3 × 10<SUP>33</SUP> erg s<SUP>-1</SUP> (0.5-10 keV). We discuss all the reported results in the framework of both spherically symmetric clumpy wind scenario and quasi-spherical settling accretion model.STAMPAenArticle10.1093/mnras/stv3412-s2.0-85015525287000355337500004https://academic.oup.com/mnras/article/449/2/1228/10711672015MNRAS.449.1228SFIS/05 - ASTRONOMIA E ASTROFISICA