  The 2009 November outburst of the neutron star X-ray binary Aquila X-1 was
observed with unprecedented radio coverage and simultaneous pointed X-ray
observations, tracing the radio emission around the full X-ray hysteresis loop
of the outburst for the first time. We use these data to discuss the disc-jet
coupling, finding the radio emission to be consistent with being triggered at
state transitions, both from the hard to the soft spectral state and vice
versa. Our data appear to confirm previous suggestions of radio quenching in
the soft state above a threshold X-ray luminosity of about 10% of the Eddington
luminosity. We also present the first detections of Aql X-1 with Very Long
Baseline Interferometry (VLBI), showing that any extended emission is
relatively diffuse, and consistent with steady jets rather than arising from
discrete, compact knots. In all cases where multi-frequency data were
available, the source radio spectrum is consistent with being flat or slightly
inverted, suggesting that the internal shock mechanism that is believed to
produce optically thin transient radio ejecta in black hole X-ray binaries is
not active in Aql X-1.
