Revisiting the 2021 Outburst of the BHC MAXI J1803-298 Using NICER, NuSTAR, and Insight-HXMT Data

TL;DR

This study analyzes the 2021 outburst of MAXI J1803-298 using multi-instrument data to understand its spectral states, LFQPO evolution, and accretion flow dynamics, providing new insights into black hole accretion behavior.

Contribution

It offers a comprehensive broadband spectral and timing analysis with spectral modeling and cospectral techniques, revealing the origin and evolution of LFQPOs in the source.

Findings

LFQPO frequency increased from 0.35 Hz to 0.5 Hz during the hard state.

Spectral modeling indicates a shock at 130 Schwarzschild radii and estimates black hole mass.

Cospectral analysis confirms the intrinsic nature of variability, reducing dead-time effects.

Abstract

We present a broadband spectral and timing study of the black hole candidate MAXI J1803-298 during its 2021 outburst using simultaneous observations from NICER, NuSTAR, and Insight-HXMT. The combined multi-instrument coverage allows us to investigate the evolution of low-frequency quasi-periodic oscillations (LFQPOs) together with the spectral properties of the source over a wide energy range. During the early observation epoch, the source exhibits a hard or hard-intermediate spectral state dominated by Comptonized emission with reflection features. Spectral modeling within the framework of the two-component advective flow (TCAF) model indicates the presence of a sub-Keplerian halo and a Keplerian disk with a shock located at 130 Schwarzschild radii, and provides an independent estimate of the black hole mass. A prominent LFQPO is detected during this epoch with a centroid frequency evolving from 0.35 Hz to 0.5 Hz and extending up to 100 keV. The energy-dependent fractional rms variability suggests that the modulation originates primarily from the Comptonizing inner accretion flow. In contrast, a later observation epoch shows a softer spectral state characterized by stronger disk emission and a steeper photon index, during which no LFQPO is detected. We also demonstrate that cospectral analysis effectively mitigates dead-time-induced distortions in NuSTAR timing studies, confirming the intrinsic nature of the detected variability. The combined spectral and timing results support a scenario in which LFQPOs in MAXI J1803-298 arise from the dynamically evolving inner accretion flow.