AstroSat Observations of the Dipping Low Mass X-ray Binary XB 1254-690

TL;DR

This paper analyzes AstroSat observations of XB 1254-690, revealing spectral state changes, flux-dependent thermal emission, and insights into the accretion disc geometry of this dipping low-mass X-ray binary.

Contribution

It provides a detailed flux-resolved spectral analysis of XB 1254-690, linking spectral components to flux levels and accretion disc structure.

Findings

Spectral states transition observed from high to low intensity.

Correlation between thermal component temperature and flux.

Insights into accretion disc geometry based on spectral analysis.

Abstract

XB 1254-690 is a neutron star low-mass X-ray binary with an orbital period of 3.88 hrs, and it exhibits energy-dependent intensity dips, thermonuclear bursts, and flares. We present the results of an analysis of a long observation of this source using the AstroSat satellite. The X-ray light curve gradually changed from a high-intensity flaring state to a low-intensity one with a few dips. The hardness intensity diagram showed that the source is in a high-intensity banana state with a gradually changing flux. Based on this, we divide the observation into four flux levels for a flux-resolved spectral study. The X-ray spectra can be explained by a model consisting of absorption, thermal emission from the disc and non-thermal emission from the corona. From our studies, we detect a correlation between the temperature of the thermal component and the flux and we examine the implications of our results for the accretion disc geometry of this source.