Associations Between Scattering Screens and Interstellar Medium Filaments

TL;DR

This study investigates the relationship between interstellar medium structures and pulsar scintillation, revealing significant alignments with HI filaments and local bubble features, suggesting magnetic fields or shocks influence these structures.

Contribution

It provides the first evidence of a strong correlation between scintillation screens and HI filaments, and re-analyzes a pulsar's scintillation screen for anisotropy.

Findings

Eight screens inside the Local Bubble.

12 out of 22 screens aligned with HI filaments.

Chance probability of observed alignments is very low.

Abstract

Pulsar scintillation can be used to measure small scale structure in the Galaxy, but little is known about the specific interstellar medium features that cause scintillation. We searched for interstellar medium 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 re-analyze its scintillation screen and find evidence for a highly anisotropic screen. Among the screens, we found that eight are located inside of the Local Bubble, and a further six are less than 100 pc farther than its inner edge. Comparisons with tracers of ionized and magnetized media did not find any new associations. Instead, for seven of the pulsars analyzed, aligned HI 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 HI filaments are preferentially associated with cold neutral gas, and thus unlikely to cause scintillation, this may indicate both the filaments and the screens are aligned preferentially by the same mechanisms such as magnetic fields or shocks.