Establishing a Connection Between the Jet and the Corona in Black Hole Low Mass X-Ray Binaries

TL;DR

This study investigates the corona–jet connection in black hole low-mass X-ray binaries during outbursts by modeling the X-ray spectrum with a lamp-post corona and tracking its height, $h$, in units of $r_g$ across three sources using NuSTAR, NICER, and Swift/XRT data. By combining this with radio jet indicators and published jet-ejection dates, the authors find a consistent pattern: coronal height increases near the time of compact-jet quenching and transient-jet launch, suggesting a coupling between the corona and the jet base or acceleration region. The results support a dynamic, potentially extended or two-component corona and magnetic coupling mechanisms, aligning with prior theoretical work and polarization/reverberation studies, while highlighting the need for higher-cadence, multi-wavelength observations to establish causality. This work advances our understanding of accretion–ejection physics in stellar-mass black holes and informs models of jet launching and corona evolution in X-ray binaries.

Abstract

Low-mass black hole X-ray Binaries (LMXBs) undergo outbursts, during which their brightness increases greatly for timescales of months. The X-ray accretion and radio jet properties change dramatically throughout an outburst in a broadly consistent way between sources. Changes to the accretion flow and the corona are evident through X-ray spectral variations, while the jet's evolution produces changes in the radio. Typically, high energy emission from the corona initially dominate the X-ray spectrum, and quasi-steady compact jets are observed in the radio. As the outburst progresses, emission from the corona fades and is superseded by lower energy X-ray accretion disk emission. During this transition, the compact jets are quenched and discrete ejecta, called transient jets, are launched. The concurrence of the corona's weakening and the jet's transition from compact to transient implies a connection, but the precise relationship has not been established. Motivated by this, we aim to investigate the corona-jet connection. We perform spectral modeling in the hard and soft X-ray, utilizing $NuSTAR$, $NICER$, and $Swift$/XRT observations to track the evolving X-ray corona for three LMXBs: MAXI J1348-630, MAXI J1535-571 and MAXI J1820+070. We use prior work to mark the presence of compact jets and the dates of discrete jet ejections. We find a clear connection between the evolution of the corona and the jet: across all three sources an increase in the distance of the corona from the black hole occurs near the time that the compact jet is quenched and the transient jet is launched.

Figures (6)

• Figure 1: Top Panel: The corona heights of MAXI J1820+070's 2018 outburst determined through X-ray spectral modeling. Bottom Panel: The evolution of the jet's radio spectral index during the same outburst. For this source we determine the radio spectral index by modeling radio flux values compiled by Echibur_Trujillo_2024 with a simple power law. Modeled heights and values of $\alpha$ change from black to red when $\alpha$ dips below $-0.25$ indicating a move towards optically thin values for the jet. Background shading represents the source's spectral states taken from Shidatsu_2019 and Homan2020. The vertical green line present in both panels indicates the date of the jet ejection according to Wood_2021. Errors on heights are estimated from our MCMCs, and are reported at 90% confidence for all epochs. In this and following figures, a radio measurement with no reported corona size indicates a lack of available NuSTAR data on that date.
• Figure 2: Top Panel: Observed corona heights of MAXI J1348--630 during its 2019 outburst, with background shading indicating the dates of spectral state transitions according to zhang. Bottom Panel: The radio spectral indices obtained by car. Values of $\alpha$ and corona height are shaded red when $\alpha < -0.25$. An increased corona height is observed around the time of both ejection events (indicated by green shading) car.
• Figure 3: Top Panel: Observed corona heights of MAXI J1535--571 during its 2017 outburst. Bottom panel: The radio/IR spectral indices from Russell_2019 for the same time period. An increase in corona at the time of jet ejections and the quenching of the compact jet is observed. Values of $\alpha$ and corona height are shaded red once the radio spectrum is $\alpha < -0.25$. Background shading represents spectral states taken from Tao_2018nakahira_2018Russell_2019. Green shading represents dates of jet ejection Russell_2019.
• Figure 4: The data and spectral model comprising each epoch of MAXI J1820+070's 2018 outburst (top panels). Bottom panels show (Data-Model)/Error. Plots are rebinned for illustrative purposes.
• Figure 5: The data and spectral model comprising each epoch of MAXI J1535--571 2017 outburst (top panels). Bottom panels show (Data-Model)/Error. Plots are rebinned for illustrative purposes.