Construction of a Pulsar Interstellar Medium Array*

Pulses from radio pulsars undergo dispersion as they pass through the ionized interstellar medium, delaying the pulses as a function of radio frequency and the dispersion measure (DM), the integrated line-of-sight electron density. DM time variability has been measured for many pulsars with both stochastic and systematic components; separating both types of variation is challenging and has led to biased physical interpretations for different lines of sight. We leverage the well-known statistical properties of autoregressive processes to model both types of variations. We invoke the physical mechanisms for turbulence and dynamics to drastically simplify the estimation of model parameters. The autoregressive approach can be extended to multiple DM timeseries to create a pulsar interstellar medium array (PISMA) with the goal of measuring correlated signatures in pulsar data due to the interstellar medium and solar wind, analogously to the observation of a pulsar timing array (PTA) with the goal of measuring correlated signatures due to gravitational waves. Using additional measurements from pulsar scintillation and scattering observations, we can globally estimate the electron-density wavenumber spectral index to test departures from the theoretical Kolmogorov model of turbulence.