The Delayed Radio Emission in the Black Hole X-Ray Binary MAXI J1348-630

Abstract

Abstract We explore the coupling between the accretion flow and the jet in black hole X-ray binary MAXI J1348-630 by analyzing the X-ray and radio observations during its 2019 outburst. We measure the time delay between the radio and Comptonization fluxes with the interpolated cross-correlation function. For the first time, we find that the radio emission lags behind the X-ray Comptonization emission by about 3 days during the rising phase covering the rising hard state and the following soft state. Such a long radio delay indicates that the Comptonization emission most likely originates from the advection-dominated accretion flow rather than the jet in this source. The Comptonization luminosity L C in 0.1–100 keV and the radio luminosity L R at 5.5 GHz, after considering the radio delay of ∼3 days, follow the correlation with a slope β = 3.04 ± 0.93, which is much steeper than the previously reported β = 0.6 or 1.40 using the total luminosity in the limited band (e.g., 1–10 keV) in the literature. This highlights the necessity of considering (1) the time delay, (2) the spectral decomposition, and (3) the broad energy band, in the radio–X-ray correlation analysis. As the jet reappears during the decaying phase (covering the soft state and the following decaying hard state) and the mini-outburst, the Componization and the radio emission appear to be almost simultaneous. And, the radio-Compton correlation during the mini-outburst becomes shallow with the correlation slope β = 1.11 ± 0.15. These indicate an intrinsic difference in the accretion–jet coupling physics between the main outburst and the mini-outburst.