2017 Outburst of H 1743-322: AstroSat and Swift View

TL;DR

This study analyzes the 2017 outburst of H 1743-322 using AstroSat and Swift data, revealing a failed outburst with specific timing and spectral features, including QPOs, soft lags, and a truncated accretion disk.

Contribution

It provides the first detailed broadband spectral and timing analysis of the 2017 outburst, highlighting the nature of failed outbursts and disk truncation in H 1743-322.

Findings

Detection of type C QPO at ~0.4 Hz

Observation of soft time lags at QPO frequencies

Evidence of a significantly truncated accretion disk

Abstract

We perform a comprehensive timing and broadband spectral analysis using an AstroSat observation of the low-mass black hole X-ray binary H~1743--322 during 2017 outburst. Additionally, we use two Swift/XRT observations, one of which is simultaneous with AstroSat and the other taken three days earlier, for timing analysis. The hardness-intensity diagram indicates that the 2017 outburst was a failed one unlike the previous successful outburst in 2016. We detect type C quasi-periodic oscillation (QPO) in the simultaneous AstroSat and Swift/XRT observations at $\sim0.4$ Hz, whereas an upper harmonic is noticed at $\sim0.9$ Hz in the AstroSat data only. Although these features are found to be energy independent, we notice a shift of $\sim0.08$ Hz in the QPO frequency over the interval of three days. We also investigate the nature of variability in the two consecutive failed outbursts in 2017 and 2018. We detect soft time lags of $23.2\pm12.2$ ms and $140\pm80$ ms at the type C QPO frequencies in 2017 Astrosat and 2018 XMM-Newton data, respectively. The lag-energy spectra from both the outbursts suggest that the soft lags may be associated with the reflection features. The broadband spectral analysis indicates that the source was in the low/hard state during our AstroSat observation. Modeling of the disk and reflection continuum suggests the presence of a significantly truncated accretion disk by at least $27.4~r_{\rm{g}}$ from the ISCO when the source luminosity is $\sim1.6\%$ of the Eddington luminosity.