A new radio census of neutron star X-ray binaries

Abstract

We report new radio observations of a sample of thirty-six neutron star (NS) X-ray binaries, more than doubling the sample in the literature observed at current-day sensitivities. These sources include thirteen weakly-magnetised (B < 1010 G) and twenty-three strongly-magnetised (B ≥ 1010 G) NSs. Sixteen of the latter category reside in high-mass X-ray binaries, of which only two systems were radio-detected previously. We detect four weakly and nine strongly-magnetised NSs; the latter are systematically radio fainter than the former and do not exceed LR ≈ 3 × 1028 erg/s. In turn, we confirm the earlier finding that the weakly-magnetized NSs are typically radio fainter than accreting stellar-mass black holes. While an unambiguous identification of the origin of radio emission in high-mass X-ray binaries is challenging, we find that in all but two detected sources (Vela X-1 and 4U 1700-37) the radio emission appears more likely attributable to a jet than the donor star wind. The strongly-magnetised NS sample does not reveal a global correlation between X-ray and radio luminosity, which may be a result of sensitivity limits. Furthermore, we discuss the effect of NS spin and magnetic field on radio luminosity and jet power in our sample. No current model can account for all observed properties, necessitating the development and refinement of NS jet models to include magnetic field strengths up to 1013 G. Finally, we discuss jet quenching in soft states of NS low-mass X-ray binaries, the radio non-detections of all observed very-faint X-ray binaries in our sample, and future radio campaigns of accreting NSs.

A multi-wavelength study of GRS 1716-249 in outburst : constraints on its system parameters

“…Fender & Hendry 2000;Fender & Kuulkers 2001), although there is strong evidence of different classes of NSXBs showing different behaviour in the radio/X-ray correlation plane (see e.g. Tudor et al 2017;van den Eijnden et al 2021). We find that a greater distance shifts GRS 1716−249 from the lower luminosity part of the outlier track (luminosities where mostly NSs are observed and the BHs seem to shift to the standard track) to the higher luminosities where the majority of the BHXB sample following the outlier track lies (see Fig.…”

Quasi-simultaneous Radio/X-Ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6−1125 during its Low-luminosity Accretion-disk State

“…More recent works, benefitting from a larger number of detected sources, show that the correlation for hard-state Atoll sources (index 1.4) should be viewed with skepticism given that this correlation was found over 1-1.5 dex in L X (Tudor et al 2017;Gallo et al 2018). Indeed, the few sources tracked over more than ∼1-2 dex in L X (mainly SAX J1808.4−3658) show significant scatter in the radio/X-ray measurements, compared to the tighter correlation observed in BH-LMXBs such as GX339-4, V404 Cyg, or XTE J1118+480.…”

“…Indeed, the few sources tracked over more than ∼1-2 dex in L X (mainly SAX J1808.4−3658) show significant scatter in the radio/X-ray measurements, compared to the tighter correlation observed in BH-LMXBs such as GX339-4, V404 Cyg, or XTE J1118+480. Furthermore, Tudor et al (2017) question the very presence of single correlation. Such studies remain limited by the low number of detected NS-LMXBs, which are typically radio-fainter than BH-LMXBs by a factor of ∼20 at a given L X .…”

“…Just as all three known tMSPs appear like the class of "redback" MSPs when they are in the rotationpowered state, some of the AMXPs appear like tMSPs in the accretion-powered state (though none of these sources have shown radio pulsations during quiescence, e.g., Patruno et al 2017). Tudor et al (2017) tracked various pulsating (IGR J17511−3057, SAX J1808.4−3658, and IGR J00291 +5934) and non-pulsating (Cen X-4) NS-LMXBs in outburst and down to quiescence. They showed that, in contrast to BH-LMXBs (which all seem to populate a radiatively inefficient track of L L R X 0.7 µ ), NS-LMXBs exhibit more diverse radio/ X-ray behaviors, possibly due to the neutron star's spin rate and magnetic field strength.…”

“…Recent works by andvan den Eijnden et al (2017) indicate that dramatic type-II X-ray bursts occur due to a gap between the neutron star and the inner edge of the accretion disk.…”