Speaker
Description
We present a detailed temporal analysis of a Type I X-ray burst from the neutron star low-mass X-ray binary (NS-LMXB) XTE J1810−189, observed on 27 April 2023 with the Neutron Star Interior Composition Explorer (NICER). The burst displays a rapid rise time of 2.55 s, followed by an exponential decay with a timescale of 7.5 s, resulting in a total burst duration of ~13 s. Type I X-ray bursts are produced by unstable thermonuclear burning of accreted material on the surface of neutron stars in NS-LMXBs. Because these bursts originate at the stellar surface, they can display highly coherent brightness modulations, known as burst oscillations, which are commonly associated with the neutron star spin frequency. In this study, we report the detection of a burst oscillation signal at a frequency of ~459 Hz during the cooling tail of the burst. The signal exhibits a strong Leahy-normalized power of PL=35.95 at 458.92 Hz, corresponding to a single-trial significance of 5.53σ and a multiple-trial significance of 3.14σ. The folded pulse profile in the 0.2–12 keV energy band is well described by a constant plus sinusoidal model, yielding a fractional root-mean-squared amplitude of 14.63%. The detected oscillation frequency is consistent with the neutron star spin, implying a spin period of ∼2.18 ms and placing XTE J1810−189 among the rapidly rotating neutron stars in the NS-LMXB population. The detection of the oscillation during the cooling phase of the burst suggests that the observed modulation may be explained by surface mode oscillations or an asymmetric cooling wake. These results provide valuable constraints on the spin properties and burst oscillation mechanisms in XTE J1810−189 and contribute to a broader understanding of thermonuclear burst phenomena in accreting neutron stars.
