gravitational wave signal, making it harder to distinguish from stationary spectral line artifacts, which tend to contaminate searches at high declination near the ecliptic pole. Hence we chose the next closest, NGC 6544, which is at a declination of less than 30 degrees and only slightly further away at $\approx 2.7$ kpc.

We restrict the search described below to sources for which the bombardment history corresponds to a characteristic spindown age older than 300 years. The figure of 300 years is mainly a practical consideration: the cost of a search rises steeply for lower spin-down ages, and 300 years proved tractable for the Cas A search [@S5CasA].

Search parameter space {#s:SPS}
----------------------

An iterative method was used to generate the parameter space to be searched. Starting with an (assumed) spin-down age no younger than 300 years, a braking index $n$ = 5 (see below), and the known distance to the globular cluster, we calculated the age-based indirect upper limit. This is an optimistic limit on the gravitational wave strain $h_0$ which assumes that all energy lost as the target neutron star spins down is radiated away as gravitational waves[@Wette2008]:

$$\label{indirect1}
h_0 \leq \frac{1}{d} \sqrt{\frac{5 G I}{2 {c}^{3}\tau (n-1)}}.$$

Here $d$ 