Parsec-scale Constraints on the Ionized Interstellar Medium with the Terzan 5 Pulsars

Over the past two years, we used a series of GBT observations to uncover at least 33 millisecond pulsars in the globular cluster Terzan 5 located in the Galactic bulge. We now have 32 timing solutions for the pulsars which give us precise positions and dispersion measures (DMs) and indicate that the DMs are dominated by variations in the integrated electron density along the slightly different sight lines towards the pulsars. At a distance of ~8.7 kpc, angular separations between the pulsars range from 0.4"-100" and correspond to projected physical separations of 0.01-4 pc, giving us a unique probe into the ionized ISM properties on these scales. Our measurement of the DM structure function toward Terzan 5 is not inconsistent with Kolmogorov-like electron density fluctuations in the ISM on scales ranging from at least 0.2-2 pc.