Probing the energy-dependent temporal nature of MAXI J1803-298 with AstroSat and NICER

TL;DR

This study analyzes the spectral and temporal evolution of MAXI J1803-298 during its outburst, revealing state transitions, QPO characteristics, and dynamic variability origins using AstroSat and NICER data.

Contribution

It provides new insights into the energy-dependent temporal behavior and variability origins of MAXI J1803-298 during its outburst, including lag reversals and spectral state transitions.

Findings

Detection of state transitions from hard to soft states.

Observation of Type-C and Type-B QPOs in different states.

Identification of lag swings between positive and negative during the outburst.

Abstract

We performed the spectral and temporal analysis of MAXI J1803-298 using AstroSat/LAXPC and NICER observations taken in May 2021 during the initial phase of the outburst. We found that the source traverses through the hard, intermediate, and soft spectral states during the outburst. The spectrum in all states can be described using soft emissions from the thermal disk and hard emissions from the coronal regions. The variation in the inner disk temperature and normalization of the disk indicates the motion of the truncated disk across these different spectral states. We confirmed the presence of broad features, Type-C, and Type-B QPOs in the power spectra of different spectral states. We investigated the fractional rms and lags of all the variability features and discovered that the lag swung between positive and negative during the outburst evolution. While modeling the features with a simple model that considers variations in accretion parameters such as the accretion rate, heating rate, and inner disk radius, along with delays between them, we found a dynamic reversal in the origin of variability between the corona and the disk. Furthermore, our results are consistent with previous works and a radio study conducted on this source during its outburst.