We investigate the time-varying electromagnetic emission of a low-mass-ratio
supermassive black hole binary (SMBHB) embedded in a circumprimary disk, with a
particular interest in variability of shocks driven by the binary. We perform a
2D, locally isothermal hydrodynamics simulation of a SMBHB with mass ratio
q=0.01 and separation a=100Rg, using a physically self-consistent steady
disk model. We estimate the electromagnetic variability from the system by
monitoring accretion onto the secondary and using an artificial viscosity
scheme to capture shocks and monitor the energy dissipated. The SMBHB produces
a wide, eccentric gap in the disk, previously only observed for larger mass
ratios, which we attribute to our disk model being much thinner
(H/R≈0.01 near the secondary) than is typical of previous works. The
eccentric gap drives periodic accretion onto the secondary SMBH on a timescale
matching the orbital period of the binary, tbin≈0.1yr,
implying that the variable accretion regime of the SMBHB parameter space
extends to lower mass ratios than previously established. Shocks driven by the
binary are periodic, with a period matching the orbital period, and the shocks
are correlated with the accretion rate, with peaks in the shock luminosity
lagging peaks in the accretion rate by 0.43tbin. We propose that
the correlation of these quantities represents a useful identifier of SMBHB
candidates, via observations of correlated variability in X-ray and UV
monitoring of AGN, rather than single-waveband periodicity alone.Comment: 12 pages, 8 figures, accepted by MNRA