MeerKAT radio observations of the neutron star low-mass X-ray binary Cen X-4 at low accretion rates

Abstract

Centaurus X-4 (Cen X-4) is a relatively nearby neutron star low-mass X-ray binary that showed outbursts in 1969 and 1979, but has not shown a full outburst since. Due to its proximity and sustained period of quiescence, it is a prime target to study the coupling between accretion and jet ejection in quiescent neutron star low-mass X-ray binaries. Here, we present four MeerKAT radio observations at 1.3 GHz of Cen X-4, combined with NICER and Swift X-ray monitoring. During the first and most sensitive observation, Cen X-4 was in a fully quiescent X-ray state. The three later and shorter observations targeted a brief period of faint X-ray activity in January 2021, which has been referred to as a 'mis-fired' outburst. Cen X-4 is not detected in any of the four MeerKAT observations. We place these radio non-detections on the X-ray -- radio luminosity diagram, improving the constraints on the correlation between the two luminosities from earlier quiescent radio studies. We confirm that Cen X-4 is radio fainter than the transitional milli-second pulsar PSR J1023+0038 at the same X-ray luminosity. We discuss the radio behaviour of accreting neutron stars at low X-ray luminosity more generally and finally comment on future observing campaigns.

12 pages, 4 figures, 2 tables. Accepted for publication in MNRAS

References in corpus (28)

• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• Modelling the behaviour of accretion flows in X-ray binaries
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• An online repository of Swift/XRT light curves of GRBs
• A radio-emitting outflow in the quiescent state of A0620-00: implications for modelling low-luminosity black hole binaries
• "Propeller" Regime of Disk Accretion to Rapidly Rotating Stars
• Black hole-like hysteresis and accretion states in neutron star low mass X-ray binaries
• The radio/X-ray domain of black hole X-ray binaries at the lowest radio luminosities
• RXTE observations of the first transient Z source XTE J1701-462: shedding new light on mass accretion in luminous neutron star LMXBs
• Strong disc winds traced throughout outbursts in black-hole X-ray binaries
• The 2015 Decay of the Black Hole X-ray Binary V404 Cygni: Robust Disk-Jet Coupling and a Sharp Transition into Quiescence
• Disk-jet coupling in low-luminosity accreting neutron stars
• Insight-HXMT discovery of the highest energy CRSF from the first Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124
• A new radio census of neutron star X-ray binaries
• A Hard X-Ray Power-Law Spectral Cutoff in Centaurus X-4
• Near-infrared emission lines trace the state-independent accretion disc wind of the black hole transient MAXI J1820+070
• Optical precursors to X-ray binary outbursts
• A persistent ultraviolet outflow from an accreting neutron star binary transient
• Jet quenching in the neutron star low-mass X-ray binary 1RXS J180408.9$-$342058
• Multiwavelength observations of the black hole X-ray binary A0620-00 in quiescence
• The hybrid radio/X-ray correlation of the black hole transient MAXI J1348-630
• A re-establishing jet during an X-ray re-brightening of the Be/X-ray binary Swift J0243.6+6124
• The Flare-Dominated Accretion Mode of a Radio-Bright Candidate Transitional Millisecond Pulsar
• The MAVERIC Survey: Variable Jet-Accretion Coupling in Luminous Accreting Neutron Stars in Galactic Globular Clusters
• The MAVERIC Survey: Simultaneous Chandra and VLA observations of the transitional millisecond pulsar candidate NGC 6652B
• Simultaneous X-ray and radio observations of the transitional millisecond pulsar candidate CXOU J110926.4-650224. The discovery of a variable radio counterpart
• A misfired outburst in the neutron star X-ray binary Centaurus X-4
• Quasi-Simultaneous Radio/X-ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125 During its Low-Luminosity Accretion-Disc State