2025MNRAS.542..443M

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 Neutron Star Interior Composition Explorer (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 Nuclear Spectroscopic Telescope Array (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 disc reflection model. As observed during the peak of the NICER bursts, the reflection model can contribute $\sim$30 per cent of the overall emission. During the NICER bursts, a correlation is observed between the flux of the blackbody and the reflection components. The measurements of the mass accretion rate indicate that the bursts may be powered by a mixed H/He fuel. Moreover, the broad-band NICER and NuSTAR spectra are also used to probe the reflection signature in the burst-free persistent region using the relativistic reflection model. Based on the variability of the count rate during the NuSTAR observation, we also investigate the evolution of spectral parameters during two different flux levels of the NuSTAR observation. The inner disc radius (R$_{\textrm {in}}$) and the angle of inclination are found to be nearly 11 $R_{g}$ and $\sim 50^{\circ }$, respectively. The magnetic field strength at the poles of the neutron star is estimated to be $B \sim 6.0 \times 10^8$ G, assuming that the inner disc is truncated at the magnetospheric boundary.