  We study the periodic forced response of a system of two limit cycle
oscillators that interact with each other via a time delayed coupling. Detailed
bifurcation diagrams in the parameter space of the forcing amplitude and
forcing frequency are obtained for various interesting limits using numerical
and analytical means. In particular, the effects of the coupling strength, the
natural frequency spread of the two oscillators and the time delay parameter on
the size and nature of the entrainment domain are delineated. The system is
found to display a nonlinear response on certain critical contours in the space
of the coupling strength and time delay. Time delay offers a novel tuning knob
for controlling the system response over a wide range of frequencies and this
may have important practical applications.
