ILLIANO, GIULIAGIULIAILLIANOPAPITTO, ALESSANDROALESSANDROPAPITTOSANNA, ANDREAANDREASANNABult, PeterPeterBultAMBROSINO, FilippoFilippoAMBROSINOMIRAVAL ZANON, ARIANNAARIANNAMIRAVAL ZANONCoti Zelati, FrancescoFrancescoCoti ZelatiSTELLA, LuigiLuigiSTELLAAltamirano, DiegoDiegoAltamiranoBaglio, Maria CristinaMaria CristinaBaglioBOZZO , ENRICOENRICOBOZZOBURDERI, LUCIANOLUCIANOBURDERIDE MARTINO, DomitillaDomitillaDE MARTINODI MARCO, AlessandroAlessandroDI MARCODi Salvo, TizianaTizianaDi SalvoFerrigno, CarloCarloFerrignoLoktev, VladislavVladislavLoktevMARINO, ALESSIOALESSIOMARINONg, MasonMasonNgPILIA, MauraMauraPILIAPoutanen, JuriJuriPoutanenSalmi, TuomoTuomoSalmi2023-03-032023-03-0320232041-8205http://hdl.handle.net/20.500.12386/33970We present a pulse timing analysis of NICER observations of the accreting millisecond X-ray pulsar SAX J1808.4−3658 during the outburst that started on 2022 August 19. Similar to previous outbursts, after decaying from a peak luminosity of ≃1 × 1036 erg s−1 in about a week, the pulsar entered a ∼1 month long reflaring stage. Comparison of the average pulsar spin frequency during the outburst with those previously measured confirmed the long-term spin derivative of ${\dot{\nu }}_{\mathrm{SD}}=-(1.15\,\pm \,0.06)\times \,{10}^{-15}$ Hz s−1, compatible with the spin-down torque of a ≈1026 G cm3 rotating magnetic dipole. For the first time in the last twenty years, the orbital phase evolution shows evidence for a decrease of the orbital period. The long-term behavior of the orbit is dominated by an ∼11 s modulation of the orbital phase epoch consistent with a ∼21 yr period. We discuss the observed evolution in terms of a coupling between the orbit and variations in the mass quadrupole of the companion star.STAMPAenTiming Analysis of the 2022 Outburst of SAX J1808.4-3658: Hints of Orbital DecayArticle10.3847/2041-8213/acad81https://iopscience.iop.org/article/10.3847/2041-8213/acad81/pdf2023ApJ...942L..40IFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering