India’s first dedicated multi-wavelength space observatory, AstroSat, has been instrumental in conducting a spectral and timing study of the Z source GX 340+0, an X-ray binary star system. The study utilized data from AstroSat’s Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC) instruments.
Decoding the Z-track Behavior
During the observation period, GX 340+0 displayed a complete Z-track, a characteristic pattern in the X-ray color-color diagram. This pattern is reflective of various spectral states, including the Horizontal, Normal, and Flaring branches (HB, NB, and FB), as well as transitions at the hard and soft apexes (HA and SA).
AstroSat’s Unique Modeling Approach
The analysis revealed that the spectral behavior of GX 340+0 is better modeled by combining a blackbody component, representing the thermal emission from the neutron star or inner accretion disk, and a hot Comptonizing corona. This approach proved more precise than models that include a disk component. The flux attributed to the Comptonized component consistently decreased along the Z-track, while the blackbody component showed non-monotonic variations in both temperature and radius, driving the Z-track behavior observed.
Uncovering Quasi-periodic Oscillations
The timing analysis exposed Quasi-periodic Oscillations (QPOs) with a notable ∼50 Hz frequency in the HB, HA, and upper NB. A different ∼6 Hz QPO was found in the other branches. These QPOs demonstrated an increase in fractional root mean square (r.m.s) with energy and were defined by soft lags in all branches except the SA and FB.
The findings from this study contribute significantly to our understanding of the complex interactions between different components of the system and their impact on the observed X-ray emission. The results underline the importance of AstroSat in advancing astrophysical research, particularly in probing the intricate dynamics of X-ray binary star systems like GX 340+0.
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