Long term radio monitoring of the neutron star X-ray binary Swift J1858.6-0814

TL;DR

This paper reports long-term radio observations of the neutron star X-ray binary Swift J1858.6-0814, revealing persistent jet activity, flares, and state-dependent radio quenching, and constrains jet magnetic fields and energies.

Contribution

It provides the first detailed radio monitoring of Swift J1858.6-0814 during outburst, linking radio and X-ray properties and exploring jet characteristics across states.

Findings

Detection of quasi-persistent, self-absorbed jet emission.

Observation of two radio flares constraining jet magnetic field and energy.

Radio emission is quenched during the soft X-ray state.

Abstract

We present the results of our long term radio monitoring campaign at 1.3GHz (MeerKAT) and 15.5GHz (Arcminute Microkelvin Imager - Large Array, AMI-LA) for the outburst of the recently discovered neutron star X-ray binary Swift J1858.6-0814. Throughout the outburst, we observe radio emission consistent with a quasi-persistent, self-absorbed jet. In addition, we see two flares at MJD 58427 and 58530. The second flare allows us to place constraints on the magnetic field and minimum energy of the jet at 0.2G and 5x10^37erg, respectively. We use the multi-frequency radio data in conjunction with data from Swift-BAT to place Swift J1858.6-0814 on the radio/X-ray correlation. We find that the quasi-simultaneous radio and BAT data makes Swift J1858.6-0814 appears to bridge the gap in the radio/X-ray plane between atoll and Z sources. Furthermore, AMI-LA observations made whilst Swift J1858.6-0814 was in the soft state have allowed us to show that the radio emission during the soft state is quenched by at least a factor of four.