Speaker
Description
How stellar-mass black holes distribute accretion power between the disc, corona and jet, and how this balance evolves throughout an outburst, is central to understanding accretion and ejection in X-ray binaries. MAXI J1348$-$630 is a black-hole X-ray transient that underwent a bright 2019 outburst followed by a reflare and several lower-luminosity mini-outbursts. Its dense radio, optical and X-ray coverage, complemented by infrared observations during the rise and peak of the main outburst, makes it an ideal laboratory to follow the coupled evolution of the disc, compact jet and corona.
I will present a multiwavelength study of MAXI J1348$-$630 based on long-term optical monitoring with the Las Cumbres Observatory telescopes, together with quasi-simultaneous ($<24$ h) radio, infrared, UV and X-ray observations where available. Using colour–magnitude diagrams, radio-to-UV spectral energy distributions, and optical/X-ray and radio/optical correlations, we find that the optical bands are generally dominated by thermal disc emission and/or X-ray reprocessing during the main outburst and later rebrightenings, with a non-negligible jet contribution at some epochs. The radio/optical flux correlation, one of the first reported for an X-ray binary, reinforces this picture, showing that the optical emission is not simply tracking the compact jet, but contains a substantial disc contribution. In contrast, the near-infrared emission is dominated by compact-jet synchrotron during the rise of the main outburst, before dropping to low levels around the hard-to-soft transition. In epochs with quasi-simultaneous radio detections, the inferred jet-break frequencies span the radio-to-OIR regime, $\nu_{\rm b}\sim10^{11} -$10$^{14}$ Hz.
I will place these broadband results in the context of published NICER spectral-timing constraints on the coronal geometry of MAXI J1348$-$630. This allows us to test whether phases of jet activity, suppression and reactivation coincide with changes in the coronal geometry, and to explore whether a vertically extended or outflow-like corona may be linked to the compact jet. Together, these results provide a disc–jet–corona view of how MAXIJ1348$-$630 reorganises during an outburst and its hard-state rebrightenings.