Eclipse Dynamics and X-ray Burst Characteristics in the Low-Mass X-ray Binary EXO 0748-676

Abstract

This study investigates the timing and spectral characteristics of X-ray bursts from the neutron star system EXO 0748-676 using the NuSTAR observatory's FPMA and FPMB instruments in the 3-79 keV range. We identify Type I X-ray bursts driven by thermonuclear explosions on the neutron star's surface, notably a significant burst at \(X = 18,479.97\), indicating rapid energy release, followed by a recoil burst at \(X = 19,463.97\), reflecting stabilization. The correlation between burst timing and the neutron star's optical period suggests modulation by its rotation and periodic accretion dynamics. Spectral modeling reveals a photon index of \( \Gamma = 1.24 \pm 0.014 \) and a cutoff energy of \( E_C = 36.20 \pm 1.04 \; \text{keV} \), indicating a hot corona around the neutron star. The measured flux of approximately \( (381.17 \pm 0.014) \times 10^{-12} \; \text{erg cm}^{-2} \text{s}^{-1} \) underscores the dynamic nature of accretion-driven systems. Calculated luminosities derived from distance estimates range from \( (3.86 \pm 0.239) \times 10^{36} \; \text{erg/s} \) to \( (2.3 \pm 0.177) \times 10^{36} \; \text{erg/s} \). Comparative analysis with prior observations from the IBIS/ISGRI instrument on the INTEGRAL satellite shows variability in emission characteristics, including softer photon indices and higher cutoff energies in 2003 and 2004. Our examination of smaller energy gaps (3-7 keV, 7-12 keV, etc.) reveals energy-dependent behavior in burst characteristics, enhancing our understanding of nuclear burning phases. Overall, these findings validate models describing Type I X-ray bursts and lay the groundwork for future investigations into similar astrophysical systems and stellar evolution processes in extreme environments.