Interstellar Holography

TL;DR

This paper advances interstellar holography by improving the reconstruction method, enabling detailed analysis of interstellar medium structures and their effects on pulsar signals with high accuracy.

Contribution

The authors develop a new optimization technique that significantly enhances the quality of interstellar holography reconstructions, allowing precise modeling of pulsar data and interstellar medium properties.

Findings

Model accurately represents pulsar data over 63 dB dynamic range

Reveals structured, highly anisotropic scattering material

Identifies a scattering tail extending beyond 100 microseconds

Abstract

The dynamic spectrum of a radio pulsar is an in-line digital hologram of the ionised interstellar medium. It has previously been demonstrated that such holograms permit image reconstruction, in the sense that one can determine an approximation to the complex electric field values as a function of Doppler-shift and delay, but to date the quality of the reconstructions has been poor. Here we report a substantial improvement in the method which we have achieved by simultaneous optimisation of the thousands of coefficients that describe the electric field. For our test spectrum of PSR B0834+06 we find that the model provides an accurate representation of the data over the full 63 dB dynamic range of the observations: residual differences between model and data are noise-like. The advent of interstellar holography enables detailed quantitative investigation of the interstellar radio-wave propagation paths for a given pulsar at each epoch of observation; we illustrate this using our test data which show the scattering material to be structured and highly anisotropic. The temporal response of the medium exhibits a scattering tail out to beyond 100 microsec and a pulse arrival time measurement at this frequency and this epoch of observation would be affected by a mean delay of 15 microsec due to multipath propagation in the interstellar medium.