Relativistic X-ray reflection and thermonuclear burst from accreting millisecond X-ray pulsar SRGA J144459.2-604207

TL;DR

This study analyzes thermonuclear bursts and relativistic X-ray reflection from the accreting millisecond X-ray pulsar SRGA J144459.2-604207 using NICER, XMM-Newton, and NuSTAR data, revealing spectral evolution, reflection features, and neutron star magnetic field estimates.

Contribution

It provides the first detailed spectral and temporal analysis of bursts and reflection features from SRGA J144459.2-604207, including estimates of the neutron star's magnetic field and disk parameters.

Findings

Reflection contributes 30% during burst peaks.

Correlation between blackbody flux and reflection during bursts.

Neutron star magnetic field estimated at 6 x 10^8 G.

Abstract

We present the results obtained from the spectral and temporal study of thermonuclear bursts from the millisecond X-ray pulsar SRGA J144459.2-604207 detected with NICER. The dynamic evolution of the spectral parameters in a broad energy range is also investigated during a simultaneously detected burst with XMM-Newton and NuSTAR. The burst profiles exhibit a strong energy dependence, as observed with XMM-Newton, NICER, and NuSTAR. We investigated the reflection feature during these bursts using the disk reflection model. As observed during the peak of the NICER bursts, the reflection model can contribute 30 per cent of the overall emission. During the NICER bursts, a correlation is observed between the flux of the blackbody and the reflection components. The measurements of the mass accretion rate indicate that the bursts may be powered by a mixed H/He fuel. Moreover, the broadband NICER and NuSTAR spectra are also used to probe the reflection signature in the burst-free persistent region using the relativistic reflection model. Based on the variability of the count rate during the NuSTAR observation, we also investigate the evolution of spectral parameters during two different flux levels of the NuSTAR observation. The inner disk radius (Rin) and the angle of inclination are found to be nearly 11 Rg and 50 degrees, respectively. The magnetic field strength at the poles of the neutron star is estimated to be 6 x 10^8 G, assuming that the inner disk is truncated at the magnetospheric boundary.