| Name: Manoj Mandal |
| Affiliation: Physical Research Laboratory |
| Conference ID: ASI2026_444 |
| Title: Discovery of burst oscillation in millisecond X-ray pulsar SRGA J144459.2-604207 |
| Abstract Type: Poster |
| Abstract Category: High Energy Phenomena, Fundamental Physics and Astronomy |
| Author(s) and Co-Author(s) with Affiliation: Manoj Mandal(PHYSICAL RESEARCH LABORATORY, Navrangpura, Ahmedabad - 380 009, India), Sachindra Naik(PHYSICAL RESEARCH LABORATORY, Navrangpura, Ahmedabad - 380 009, India) |
| Abstract: Burst oscillations during thermonuclear X-ray bursts arise from brightness asymmetries on the neutron star (NS) surface and are typically observed at or near the NS spin frequency. We report the discovery of burst oscillations from the newly discovered accreting millisecond X-ray pulsar SRGA J144459.2−604207, based on a comprehensive timing analysis of 39 thermonuclear bursts observed with NICER, XMM-Newton, and NuSTAR during its 2024 outburst. Significant oscillations were detected at frequencies of 447.7–448.0 Hz, consistent with the known spin frequency of the NS. The strongest signals reached single-trial significances of 5.1σ in the XMM-Newton data and 5.2σ in the NuSTAR data, with maximum Z1^2 powers of ∼32. We performed 50,000 Monte Carlo simulations to estimate the null distribution of the maximum power, and none produced a value exceeding the observed maximum, demonstrating that the signal is highly significant. The folded pulse profiles are well described by a sinusoidal function, with fractional rms amplitudes of ∼8.5% in the 0.5–10 keV band and ∼21% in the 3–40 keV band.
The physical origin of burst oscillations remains uncertain. They are generally attributed to localized hot spots formed during ignition and early flame spreading on the neutron-star surface, although the geometry and propagation of the burning front are poorly constrained. While large amplitudes observed early in bursts are consistent with this scenario, oscillations detected during the burst tail are more difficult to explain and may instead arise from hydrodynamic instabilities in the neutron-star ocean or from global surface modes. It also remains unclear why burst oscillations are observed only in some accreting millisecond X-ray pulsars or why they appear intermittently within a given source. Despite these uncertainties, burst oscillations provide a valuable probe of thermonuclear burning and neutron-star surface physics.
|
