NICER / ISS Science Nugget for March 28, 2019

State transition and radio flare in MAXI J1820+070

NICER's coverage of the black-hole binary source MAXI J1820+070 has provided a powerful framework for the interpretation of multi-wavelength studies of this source (see figure below). For example, combined with radio coverage, NICER observations enabled a study of the connection between rapid changes in variability properties and the launch of relativistic jet ejecta.

The strong flare in the radio light-curve indicates that such an event occurred late on July 6, 2018. The inferred launch time is marked with a red line in all panels of the figure. From the dynamical power spectrum in panel (f) it is clear that this launch occurred within an hour of a pronounced change in the variability properties; a pair of quasi-periodic oscillations (QPOs) that steadily increased in frequency to 8 and 16 Hz was suddenly replaced by a single, short-lived QPO around 4 Hz.

A connection between such variability and relativistic jet launches had been suggested by past RXTE observations of other black hole transients, but uncertainties were on the order of ± 1 day or more. With the NICER dataset this connection is considerably strengthened and the observed delay (>1 hour) is consistent with the time it takes for the ejecta to become optically thin and thus visible in the radio band. The 7-12 keV light-curve shown in panel (e) further indicates that the ~4 Hz QPO is related to a brief flare in the high-energy emission, possibly originating from a reenergized jet base.