to indirect upper limits derived from galactic neutron-star population simulations [@KnispelAllen].

Directed searches sit between these two extremes. As in the all-sky case, their targets are neutron stars not seen as pulsars, so that the frequency and other parameters are unknown. They focus, however, on a known sky location (and therefore a known detector-frame Doppler modulation). This directionality allows for searching over a wide range of frequencies and frequency derivatives while remaining much cheaper computationally than an all-sky search without sacrificing sensitivity. This approach was first used in a search for the accreting neutron star in the low-mass X-ray binary Sco X-1 [@S2Fstat; @S4radiometer; @S5Stochastic].

The search for the in the Cassiopeia A (Cas A)[@S5CasA] was the first directed search for a young neutron star without electromagnetically detected pulsation, motivated by the idea that young neutron stars might be promising emitters of continuous . The Cas A search [@S5CasA] set upper limits on strain which beat an indirect limit derived from energy conservation and the age of the remnant [@Wette2008] over a wide frequency band. Other directed searches have since followed in its footsteps, using different data analysis methods, for supernova 1987A and unseen neutron stars near the galactic center 