  We suggest the possibility of including millisecond pulsars inside the core
of globular clusters in pulsar timing array experiments. Since they are very
close to each other, their gravitational wave induced timing residuals are
expected to be almost the same, because both the Earth and the pulsar terms are
correlated. We simulate the expected timing residuals, due to the gravitational
wave signal emitted by a uniform supermassive black-hole binary population, on
the millisecond pulsars inside a globular cluster core. In this respect, Terzan
5 has been adopted as a globular cluster prototype and, in our simulations, we
adopted similar distance, core radius, and number of millisecond pulsars
contained in it. Our results show that the presence of a strong correlation
between the timing residuals of the globular cluster core millisecond pulsars
can provide a remarkable gravitational wave signature. This result can be
therefore exploited for the detection of gravitational waves through pulsar
timing, especially in conjunction with the standard cross-correlation search
carried out by the pulsar timing array collaborations.
