Spectral Analysis of the Black Hole X-Ray Binary Maxi J1820+070 Using Astrosat/SXT Observations

Abstract

MAXI J1820+070 is one of the brightest Galactic black hole X-ray transients discovered in recent years and has been extensively studied because of its remarkable spectral and timing behaviour. In the present work, we present timing (light-curve) and spectral analyses of MAXI J1820+070 using archival observations obtained with the Soft X-ray Telescope (SXT) onboard AstroSat. The analysis is based on a combined effective exposure of approximately 12 ks obtained from multiple orbital segments corresponding to Observation ID A05_142T01_9000002904. The source light curve exhibits significant variability, indicating active accretion processes around the compact object. Spectral fitting was performed in the 0.7–7.0 keV energy range using the model TBabs × (diskbb + powerlaw). The best-fit parameters are NH = 0.15 × 1022 cm-2 (fixed), inner disk temperature Tin = 0.145 ± 0.011 keV, and photon index Г= 0.94 ± 0.15. The fit yields χ2 = 59.39 for 38 degrees of freedom (reduced χ2 = 1.56), indicating an acceptable fit to the observed spectrum. The results indicate the presence of a relatively cool accretion disk together with a dominant hard X-ray component, suggesting that coronal emission contributes significantly to the observed X-ray spectrum. The observed variability and spectral characteristics are consistent with an active accretion state during the observation. These findings provide insight into the accretion geometry and X-ray emission mechanisms operating in MAXI J1820+070.