AstroSat Observation of X-ray Dips and State Transition in the Black Hole Candidate MAXI J1803-298

TL;DR

This study analyzes AstroSat data of MAXI J1803-298, revealing periodic dips, state transitions, and evolving QPOs, providing insights into the accretion processes and black hole properties.

Contribution

It presents the first broadband X-ray timing and spectral analysis of MAXI J1803-298 during a state transition, identifying dips, QPO evolution, and spectral features.

Findings

Detected four periodic absorption dips with 7-hour periodicity.

Observed a type-C QPO with frequency evolving from 5.31 to 7.61 Hz.

Estimated black hole mass between 3.5 and 12.5 solar masses.

Abstract

We present the results obtained from broadband X-ray timing and spectral analysis of black hole candidate MAXI J1803-298 using an AstroSat observation on May 11-12, 2021. Four periodic absorption dips with a periodicity of $7.02 \pm 0.18$ hour are detected in the light curve. AstroSat observe the source when it was undergoing a transition from hard-intermediate state to soft-intermediate state. Our timing analysis reveals the presence of a sharp type-C quasi periodic oscillation (QPO) in the power density spectra (PDS) with an evolving QPO frequency ranging from $5.31 \pm 0.02$ Hz to $7.61\pm 0.09$ Hz. We investigate the energy dependence of the QPO and do not find this feature in the PDS above 30 keV. The combined $0.7-80$ keV SXT and LAXPC spectra are fitted with a model consisting of thermal multi-colour blackbody emission and Comptonized emission components. We perform time-resolved spectroscopy by extracting spectra during the dip and non-dip phases of the observation. A neutral absorber is detected during the dip and non-dip phases though a signature of an ionized absorber is also present in the dip phases. The spectral and temporal parameters are found to evolve during our observation. We estimate the mass function of the system as $f(M) = 2.1-7.2~M_{\odot}$ and the mass of the black hole candidate in the range of $M_{\rm BH} \sim 3.5-12.5~M_{\odot}$.