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

Abstract

We present multiwavelength fast timing observations of the black hole X-ray binary MAXI J1820+070 (ASASSN-18ey), takenwith the Karl G. Jansky Very Large Array (VLA), Atacama Large Millimeter/Sub-Millimeter Array (ALMA), Very LargeTelescope (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 characterizethe variability properties in our data, we implemented a combination of cross-correlation and Fourier analyses. We find thatthe emission is highly correlated between different bands, measuring time-lags ranging from hundreds of milliseconds betweenthe X-ray/optical bands to minutes between the radio/sub-mm bands. Our Fourier analysis also revealed, for the first time in ablack hole X-ray binary, an evolving power spectral shape with electromagnetic frequency. Through modelling these variabilityproperties, we find that MAXI J1820+070 launches a highly relativistic (Τ = 6.81+1.06−1.15) and confined (φ = 0.45+0.13 −0.11 deg) jet,which is carrying a significant amount of power away from the system (equivalent to ∼ 0.6L1−100keV). We additionally placeconstraints on the jet composition and magnetic field strength in the innermost jet base region. Overall, this work demonstratesthat time-domain analysis is a powerful diagnostic tool for probing jet physics, where we can accurately measure jet propertieswith time-domain measurements alone.

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