The tidal disruption of a star by a supermassive black hole can result in transient radio emission .
The electrons producing these synchrotron radio flares could either be accelerated inside a relativistic jet or externally by shocks resulting from an outflow interacting with the circumnuclear medium .
Until now , evidence for the internal emission mechanism has been lacking ; nearly all tidal disruption flare studies have adopted the external shock model to explain the observed properties of radio flares .
Here we report a result that presents a challenge to external emission models : we discovered a cross-correlation between the soft X-ray ( 0.3-1 keV ) and 16 GHz radio flux of the tidal disruption flare ASASSN-14li .
Variability features in the X-ray light curve appear again in the radio light curve , but after a time lag of 12 ^ { +6 } _ { -5 } days .
This demonstrates that soft X-ray emitting accretion disk regulates the radio emission .
This coupling appears to be inconsistent with all previous external emission models for this source but is naturally explained if the radio emission originates from a freely expanding jet .
We show that emission internal to an adiabatically expanding jet can also reproduce the observed evolution of the radio spectral energy distribution .
Furthermore , both the correlation between X-ray and radio luminosity as well as our radio spectral modeling imply an approximately linear coupling between the accretion rate and jet power .