Pintore, FabioFabioPintoreSanna, A.A.SannaRiggio, A.A.RiggioDi Salvo, T.T.Di SalvoMEREGHETTI, SandroSandroMEREGHETTIBozzo, E.E.BozzoSánchez-Fernández, C.C.Sánchez-FernándezBurderi, L.L.BurderiIaria, R.R.Iaria2020-10-122020-10-1220180035-8711http://hdl.handle.net/20.500.12386/27740SAX J1748.9-2021 is an accreting X-ray millisecond pulsar observed in outburst five times since its discovery in 1998. In early October 2017, the source started its sixth outburst, which lasted only ∼13 days, significantly shorter than the typical 30 days duration of the previous outbursts. It reached a 0.3-70 keV unabsorbed peak luminosity of ∼3 × 10<SUP>36</SUP> erg s<SUP>-1</SUP>. This is the weakest outburst ever reported for this source to date. We analysed almost simultaneous XMM-Newton, NuSTAR, and INTEGRAL observations taken during the decaying phase of its 2017 outburst. We found that the spectral properties of SAX J1748.9-2021 are consistent with an absorbed Comptonization plus a blackbody component. The former, characterized by an electron temperature of ∼20 keV, a photon index of ∼1.6-1.7 keV, and seed photon temperature of 0.44 keV, can be associated to a hot corona or the accretion column, while the latter is more likely originating from the neutron star surface (kT<SUB>bb</SUB> ∼ 0.6 keV, R<SUB>bb</SUB> ∼ 2.5 km). These findings suggest that SAX J1748.9-2021 was observed in a hard spectral state, as it is typically the case for accreting millisecond pulsars in outburst.STAMPAenArticle10.1093/mnras/sty17352-s2.0-85051481836000441382300090https://academic.oup.com/mnras/article/479/3/4084/50473172018MNRAS.479.4084PFIS/05 - ASTRONOMIA E ASTROFISICA