Disk-jet coupling changes as a possible indicator for outbursts from GX 339-4 remaining within the X-ray hard state

• Published in: arXiv.org
• Main Authors: S E M de Haas, Russell, T D, Degenaar, N, Markoff, S, Tetarenko, A J, Tetarenko, B E, van den Eijnden, J, Miller-Jones, J C A, Parikh, A S, Plotkin, R M, Sivakoff, G R
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 09.12.2020
• Subjects: Coupling; Deposition; Luminosity; Outbursts; Physics - High Energy Astrophysical Phenomena; Radio; Radio sources (astronomy); X ray binaries; X ray spectra; X ray stars
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2012.05206

We present quasi-simultaneous radio, (sub-)millimetre, and X-ray observations of the Galactic black hole X-ray binary GX 339-4, taken during its 2017--2018 outburst, where the source remained in the hard X-ray spectral state. During this outburst, GX 339-4 showed no atypical X-ray behaviour that may act as a indicator for an outburst remaining within the hard state. However, quasi-simultaneous radio and X-ray observations showed a flatter than expected coupling between the radio and X-ray luminosities (with a best fit relation of \(L_{\rm radio} \propto L_{\rm X}^{0.39 \pm 0.06}\)), when compared to successful outbursts from this system (\(L_{\rm radio} \propto L_{\rm X}^{0.62 \pm 0.02}\)). While our 2017--2018 outburst data only span a limited radio and X-ray luminosity range (\(\sim\)1 order of magnitude in both, where more than 2-orders of magnitude in \(L_{\rm X}\) is desired), including data from other hard-only outbursts from GX 339-4 extends the luminosity range to \(\sim\)1.2 and \(\sim\)2.8 orders of magnitude, respectively, and also results in a flatter correlation (where \(L_{\rm radio} \propto L_{\rm X}^{0.46 \pm 0.04}\)). This result is suggestive that for GX 339-4 a flatter radio -- X-ray correlation, implying a more inefficient coupling between the jet and accretion flow, could act as an indicator for a hard-only outburst. However, further monitoring of both successful and hard-only outbursts over larger luminosity ranges with strictly simultaneous radio and X-ray observations is required from different, single sources, to explore if this applies generally to the population of black hole X-ray binaries, or even GX 339-4 at higher hard-state luminosities.