SANNA, ALBERTOALBERTOSANNABozzo, E.E.BozzoPAPITTO, ALESSANDROALESSANDROPAPITTORiggio, A.A.RiggioFerrigno, C.C.FerrignoDi Salvo, T.T.Di SalvoIaria, R.R.IariaMazzola, S.M.S.M.MazzolaD'AMICO, NICOLO'NICOLO'D'AMICOBurderi, L.L.Burderi2021-01-212021-01-2120180004-6361http://hdl.handle.net/20.500.12386/29938We report the detection of X-ray pulsations at 2.1 ms from the known X-ray burster IGR J17379-3747 using XMM-Newton. The coherent signal shows a clear Doppler modulation from which we estimate an orbital period of 1.9 h and a projected semi-major axis of 8 lt-ms. Taking into account the lack of eclipses (inclination angle of <75°) and assuming a neutron star mass of 1.4 M☉, we have estimated a minimum companion star of 0.06 M☉. Considerations on the probability distribution of the binary inclination angle make the hypothesis of a main-sequence companion star less likely. On the other hand, the close correspondence with the orbital parameters of the accreting millisecond pulsar SAX J1808.4-3658 suggests the presence of a bloated brown dwarf. The energy spectrum of the source is well described by a soft disk black-body component (kT 0.45 keV) plus a Comptonisation spectrum with photon index 1.9. No sign of emission lines or reflection components are significantly detected. Finally, combining the source ephemerides estimated from the observed outbursts, we obtained a first constraint on the long-term orbital evolution of the order of Ṗ_orb = (-2.5 ± 2.3) × 10^-12 s s^-1.STAMPAenArticle10.1051/0004-6361/2018332052-s2.0-85062298044000442744100001https://www.aanda.org/articles/aa/abs/2018/08/aa33205-18/aa33205-18.html2018A&A...616L..17SFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_10 High energy and particle astronomy – X-rays, cosmic rays, gamma rays, neutrinos