# The 2019 outburst of AMXP SAX J1808.4-3658 and radio follow up of MAXI J0911-655 and XTE J1701-462

## TL;DR

This study presents detailed radio, X-ray, and optical observations of the 2019 outburst of SAX J1808.4-3658, revealing jet behavior, refining luminosity correlations, and providing upper limits for other X-ray binaries, enhancing understanding of accretion-jet coupling.

## Contribution

It offers the first detailed radio follow-up of SAX J1808.4-3658's 2019 outburst and refines the radio:X-ray luminosity correlation for this source.

## Key findings

- Radio re-brightening during reflaring indicates jet strengthening.
- Refined the radio:X-ray luminosity correlation for SAX J1808.4-3658.
- Confirmed persistent background radio structures near XTE J1701-462.

## Abstract

We present radio coverage of the 2019 outburst of the accreting millisecond X-ray pulsar SAX J1808.4-3658, obtained with MeerKAT. We compare these data to contemporaneous X-ray and optical measurements in order to investigate the coupling between accretion and jet formation in this system, while the optical lightcurve provides greater detail of the outburst. The reflaring activity following the main outburst peak was associated with a radio re-brightening, indicating a strengthening of the jet in this phase of the outburst. We place quasi-simultaneous radio and X-ray measurements on the global radio:X-ray plane for X-ray binaries, and show they reside in the same region of luminosity space as previous outburst measurements, but significantly refine the correlation for this source. We also present upper limits on the radio emission from the accreting millisecond X-ray pulsar MAXI J0911-655 and the transitional Z/Atoll-type transient XTE J1701-462. In the latter source we also confirm that nearby large-scale structures reported in previous radio observations of the source are persistent over a period of ~15 years, and so are almost certainly background radio galaxies and not associated with the X-ray transient.