Associations between Scattering Screens and Interstellar Medium Filaments

Abstract Pulsar scintillation can be used to measure small-scale structure in the Galaxy, but little is known about the specific interstellar medium (ISM) features that cause scintillation. We searched for ISM counterparts to all scintillation screens for which absolute distances and scattering orientations have been measured—a sample of 12 pulsars and 22 screens. For one pulsar, PSR J0737–3039A, we reanalyze its scintillation screen and find evidence for a highly anisotropic screen. Comparisons with tracers of ionized media did not find any new associations. Instead, for seven of the pulsars analyzed, aligned H i filaments are seen for at least one of their screens, for a total of 12 out of 22 screens. This result seems unlikely to be due to chance: Comparing with random trials, we estimate a likelihood of finding 12 or more screens with aligned emission by chance of only 0.004%. Estimating the significance of the amount of aligned emission (in standard deviations over the mean), the probability of finding as much observed aligned emission by chance is larger, at 1.7%, but still indicative of a real correlation. Since H i filaments are preferentially associated with cold neutral gas, and thus unlikely to cause scintillation, this may indicate that both the filaments and the screens are aligned preferentially by the same mechanisms, such as magnetic fields or shocks.