The hybrid radio/X-ray correlation of the black hole transient MAXI J1348-630

TL;DR

This study analyzes the radio and X-ray emission correlation in the black hole binary MAXI J1348-630 during its 2019/2020 outburst, revealing a unique hybrid correlation pattern across a wide luminosity range.

Contribution

It presents the first detailed analysis of the hybrid radio/X-ray correlation in MAXI J1348-630, showing deviations from known patterns at different luminosities.

Findings

MAXI J1348-630 is an outlier at high luminosities.

It exhibits a hybrid correlation, switching tracks at specific luminosities.

Transitions occur at lower luminosities than in similar sources.

Abstract

Black hole low mass X-ray binaries in their hard spectral state are found to display two different correlations between the radio emission from the compact jets and the X-ray emission from the inner accretion flow. Here, we present a large data set of quasi-simultaneous radio and X-ray observations of the recently discovered accreting black hole MAXI J1348-630 during its 2019/2020 outburst. Our results span almost six orders of magnitude in X-ray luminosity, allowing us to probe the accretion-ejection coupling from the brightest to the faintest phases of the outburst. We find that MAXI J1348-630 belongs to the growing population of outliers at the highest observed luminosities. Interestingly, MAXI J1348-630 deviates from the outlier track at $L_{\rm X} \lesssim 7 \times 10^{35} (D / 2.2 \ {\rm kpc})^2$ erg s$^{-1}$ and ultimately rejoins the standard track at $L_{\rm X} \simeq 10^{33} (D / 2.2 \ {\rm kpc})^2$ erg s$^{-1}$, displaying a hybrid radio/X-ray correlation, observed only in a handful of sources. However, for MAXI J1348-630 these transitions happen at luminosities much lower than what observed for similar sources (at least an order of magnitude). We discuss the behaviour of MAXI J1348-630 in light of the currently proposed scenarios and we highlight the importance of future deep monitorings of hybrid correlation sources, especially close to the transitions and in the low luminosity regime.