Measuring fundamental jet properties with multiwavelength fast timing of the black hole X-ray binary MAXI J1820+070

We present multiwavelength fast timing observations of the black hole X-ray binary MAXI J1820+070 (ASASSN-18ey), taken with the Karl G. Jansky Very Large Array (VLA), Atacama Large Millimeter/Sub-Millimeter Array (ALMA), Very Large Telescope (VLT), New Technology Telescope (NTT), Neutron Star Interior Composition Explorer (NICER), and XMM-Newton. Our data set simultaneously samples 10 different electromagnetic bands (radio - X-ray) over a 7-h period during the hard state of the 2018-2019 outburst. The emission we observe is highly variable, displaying multiple rapid flaring episodes. To characterize the variability properties in our data, we implemented a combination of cross-correlation and Fourier analyses. We find that the emission is highly correlated between different bands, measuring time-lags ranging from hundreds of milliseconds between the X-ray/optical bands to minutes between the radio/sub-mm bands. Our Fourier analysis also revealed, for the first time in a black hole X-ray binary, an evolving power spectral shape with electromagnetic frequency. Through modelling these variability properties, we find that MAXI J1820+070 launches a highly relativistic (Gamma = 6.81(-1.15)(+1.06)) and confined (phi = 0.45(-0.11)(+0.13) deg) jet, which is carrying a significant amount of power away from the system (equivalent to similar to 0.6 L1-100keV). We additionally place constraints on the jet composition and magnetic field strength in the innermost jet base region. Overall, this work demonstrates that time-domain analysis is a powerful diagnostic tool for probing jet physics, where we can accurately measure jet properties with time-domain measurements alone.

Automated summary

This study presents multiwavelength fast timing observations of the black hole X-ray binary MAXI J1820+070, revealing highly correlated emission between different bands with time-lags ranging from milliseconds to minutes. Additionally, an evolving power spectral shape with electromagnetic frequency is observed for the first time in a black hole X-ray binary. The study demonstrates the power of time-domain analysis in probing jet physics and accurately measuring jet properties.