2026ApJ...998..338G

We conducted a systematic study of two thermonuclear type I X-ray bursts (B1 and B2) and the spectral properties of the bright atoll type neutron star low-mass X-ray binary 4U 1705-44 using NICER observation. In our analysis, a burst oscillation at ∼702 Hz was detected during the double-peaked profile of burst B1. This provides the first strong evidence for the spin frequency of the neutron star, which establishes 4U 1705-44 as a rapid rotator. The measured convexity parameters of the bursts indicate that both bursts likely ignited at off-equatorial latitudes. The ignition depth of burst B1 was nearly twice that of B2, indicating substantial fuel consumption between the two events. The recurrence time of B2 (∼1 hr) categorizes it as a short waiting time burst. The complementary spectral analysis of persistent emission, modeled with tbabs×(nthcomp+ diskbb), showed a hard state with a photon index Γ < 1.12. The hardness-intensity diagram was consistent with the source being in the island state. Notably, the accretion disk appeared to extend close to the neutron star surface.