X-Ray spectral and temporal properties of LMXB 4U 1608-52- observed with AstroSat and NICER

TL;DR

This study analyzes the spectral and timing properties of the neutron star X-ray binary 4U 1608-52 during outbursts, revealing stable disk radius and variable accretion-related parameters through combined AstroSat and NICER observations.

Contribution

It provides a detailed spectral and timing analysis of 4U 1608-52 using multi-instrument data, highlighting the stability of the disk radius and the role of accretion rate variations.

Findings

Inner disk radius remains stable during outbursts.

Variations in X-ray emission are driven by accretion rate changes.

Temporal and spectral analyses are consistent with each other.

Abstract

We report results from a detailed study of the neutron star X-ray binary, 4U 1608-52 using observations with {\it AstroSat} (LAXPC/SXT) and {\it NICER} during its 2016 and 2020 outbursts. The 0.7--20.0 keV spectra could be well described with the disk blackbody and thermal Comptonization model. The best-fitting inner disk temperature is $\sim$ 1 keV and radius { $\sim$ 22.17$^{+2.57}_{-2.38}$--27.19$^{+2.03}_{-1.85}$} km and no significant evolution was observed in the disk radius after performing flux and time-resolved spectroscopy. We used a multi-Lorentzian approach to fit the power density spectra and obtained broad-band noise variability. We estimated the energy-dependent fractional root mean square and time-lag of the broad-band noise, and these variations are quantitatively modelled as being due to the coherent variation of the disk emission and the coronal heating rate. Thus, the rapid temporal modeling is consistent with the longer term spectral evolution where the inner disk radius does not vary, and instead the variations can be attributed to accretion rate variations which changes the inner disk temperature and the coronal heating rate.