Pulsar timing probes of primordial black holes and subhalos

Pulsars act as accurate clocks, sensitive to gravitational redshift and acceleration induced by transiting clumps of matter. We study the sensitivity of pulsar timing arrays (PTAs) to single transiting compact objects, focusing on primordial black holes and compact subhalos in the mass range from 10(-12) M-circle dot to well above 100 M-circle dot. We find that the square kilometer array can constrain such objects to be a subdominant component of the dark matter over this entire mass range, with sensitivity to a dark matter subcomponent reaching the subpercent level over significant parts of this range. We also find that PTAs offer an opportunity to probe substantially less dense objects than lensing because of the large effective radius over which such objects can be observed, and we quantify the subhalo concentration parameters which can be constrained.