  We present a broadband radio study of the transient jets ejected from the
black hole candidate X-ray binary MAXI J1535-571, which underwent a prolonged
outburst beginning on 2 September 2017. We monitored MAXI J1535-571 with the
Murchison Widefield Array (MWA) at frequencies from 119 to 186 MHz over six
epochs from 20 September to 14 October 2017. The source was
quasi-simultaneously observed over the frequency range 0.84-19 GHz by UTMOST
(the upgraded Molonglo Observatory Synthesis Telescope), the Australian Square
Kilometre Array Pathfinder, the Australia Telescope Compact Array (ATCA), and
the Australian Long Baseline Array (LBA). Using the LBA observations from 23
September 2017, we measured the source size to be $34\pm1$ mas. During the
brightest radio flare on 21 September 2017, the source was detected down to 119
MHz by the MWA, and the radio spectrum indicates a turnover between 250 and 500
MHz, which is most likely due to synchrotron self-absorption (SSA). By fitting
the radio spectrum with a SSA model and using the LBA size measurement, we
determined various physical parameters of the jet knot (identified in ATCA
data), including the jet opening angle (= $4.5\pm1.2^{\circ}$) and the magnetic
field strength (= $104^{+80}_{-78}$ mG). Our fitted magnetic field strength
agrees reasonably well with that inferred from the standard equipartition
approach, suggesting the jet knot to be close to equipartition. Our study
highlights the capabilities of the Australian suite of radio telescopes to
jointly probe radio jets in black hole X-ray binaries (BH-XRBs) via
simultaneous observations over a broad frequency range, and with differing
angular resolutions. This suite allows us to determine the physical properties
of XRB jets. Finally, our study emphasizes the potential contributions that can
be made by the low-frequency part of the Square Kilometre Array (SKA-Low) in
the study of BH-XRBs.
