Radio monitoring of transient Be/X-ray binaries and the inflow-outflow coupling of strongly-magnetized accreting neutron stars

J van den Eijnden*, N Degenaar, T D Russell, J C A Miller-Jones, A Rouco Escorial, R Wijnands, G R Sivakoff, J V Hernández Santisteban

*Corresponding author for this work

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Strongly-magnetized (B ≥ 1012 G) accreting neutron stars (NSs) are prime targets for studying the launching of jets by objects with a solid surface; while classical jet-launching models predict that such NSs cannot launch jets, recent observations and models argue otherwise. Transient Be/X-ray binaries (BeXRBs) are critical laboratories for probing this poorly-explored parameter space for jet formation. Here, we present the coordinated monitoring campaigns of three BeXRBs across four outbursts: giant outbursts of SAX 2103.5+4545, 1A 0535+262, and GRO J1008-57, as well as a Type-I outburst of the latter. We obtain radio detections of 1A 0535+262 during ten out of twenty observations, while the other targets remained undetected at typical limits of 20–50μJy. The radio luminosity of 1A 0535+262 positively correlates with its evolving X-ray luminosity, and inhabits a region of the LXLR plane continuing the correlation observed previously for the BeXRB Swift J0243.6+6124. We measure a BeXRB LX–LR coupling index of β = 0.86 ± 0.06 (L∝ LßR ), similar to the indices measured in NS and black hole low-mass X-ray binaries. Strikingly, the coupling’s LR normalization is ∼275 and ∼6.2 × 103 times lower than in those two comparison samples, respectively. We conclude that jet emission likely dominates during the main peak of giant outbursts, but is only detectable for close-by or super-Eddington systems at current radio sensitivities. We discuss these results in the broader context of X-ray binary radio studies, concluding that our results suggest how supergiant X-ray binaries may host a currently unidentified additional radio emission mechanism.
Original languageEnglish
Article number516
Pages (from-to)4844–4861
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date8 Sept 2022
Publication statusPublished - Nov 2022


  • Accretion, accretion discs
  • Dtars: neutron
  • X-rays: binaries


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