AstroSat Observation of 2016 Outburst of H 1743-322

TL;DR

This paper reports the detection of type C QPOs and harmonic features in AstroSat data of H 1743-322 during its 2016 outburst, revealing energy-independent QPO frequencies, a low/hard state, and accretion flow fluctuations.

Contribution

First detection of specific QPO features in AstroSat data of H 1743-322, highlighting geometrical changes and accretion dynamics during outburst.

Findings

QPO and harmonic frequencies shifted compared to later observations

QPO centroid frequency is energy-independent

Detected hard lag of ~21 ms indicating accretion flow propagation

Abstract

We present the detection of type C quasi-periodic oscillation (QPO) along with upper harmonic at respective frequencies of $\sim0.6$ Hz and $\sim1.2$ Hz in the single AstroSat observation taken during the 2016 outburst of the low-mass black hole X-ray binary H~1743--322. These frequencies are found to be shifted by $\sim0.4$ Hz for the QPO and $\sim0.8$ Hz for the upper harmonic with respect to that found in the simultaneous \textit{XMM-Newton} and \textit{NuSTAR} observation taken five days later than the AstroSat observation, indicating a certain geometrical change in the system. However, the centroid frequency of the QPO and the upper harmonic do not change with energy, indicating the energy-independent nature. The decreasing trend in the fractional rms of the QPO with energy is consistent with the previous results for this source in the low/hard state. The value of the photon index ($\Gamma\sim1.67$) also indicates that the source was in the low/hard state during this particular observation. In addition, similar to the \textit{XMM-Newton} observations during the same outburst, we find a hard lag of $\sim21$ ms in the frequency range of $\sim1-5$ Hz. The log-linear trend between the averaged time lag and energy indicates the propagation of fluctuations in the mass accretion rate from outer part of the accretion disk to the inner hot regions.