paper

Evaluating the jet/accretion coupling of Aql X-1: probing the contribution of accretion flow spectral components

arXiv:2204.10910 · doi:10.1093/mnras/stad548

Abstract

The coupling between radio and X-ray luminosity is an important diagnostic tool to study the connection between the accretion inflow and jet outflow for low-mass X-ray binaries (LMXBs). When comparing NS- and BH-LMXBs, we find that the radio/X-ray correlation for individual NS-LMXBs is scattered, whereas for individual BH-LMXBs a more consistent correlation is generally found. Furthermore, we observe jet quenching for both types of LMXBs, but it is unclear what exactly causes this, and if jets in NS-LMXBs quench as strongly as those in BH-LMXBs. While additional soft X-ray spectral components can be present for NS-LMXBs due to the presence of the neutron star's surface, disentangling the individual X-ray spectral components has thus far not been considered when studying the radio/X-ray coupling. Here we present eleven epochs of Swift/XRT observations matched with quasi-simultaneous archival radio observations of the 2009 November outburst of Aql X-1. We decompose the thermal and Comptonised spectral components in the Swift/XRT spectra, with the aim of studying whether the presence of additional thermal emission affects the coupling of the radio/X-ray luminosity. We find that there is no evidence of a significant thermal contribution in Swift/XRT spectra that could cause scatter in the radio/X-ray coupling. However, a noteworthy finding is that the X-ray observation with the strongest statistically significant thermal component occurs around the same epoch as a bright radio detection. Follow-up research using more sensitive X-ray observations combined with densely sampled near-simultaneous radio observations is required to explore the radio/X-ray coupling for NS-LMXBs in more detail.

14 pages (12 main, 2 appendix), 12 figures, 4 tables. Accepted for publication in MNRAS

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