The interstellar medium as a foreground signal for Pulsar Timing Arrays 

Pulsar bow shock scattering a radio beam. (Credit: Carl Knox, Swinburne/OzGrav)

Abstract

The ionised interstellar medium (IISM) disperses and scatters the pulsed radio emission from pulsars. Pulsar timing array (PTA) observations of millisecond pulsars are sensitive to sub-microsecond delays to pulse arrival times, accumulated as the pulses traverse the IISM and heliosphere. The same observations reveal scintillation, giving a second probe of small-scale interstellar plasma. In this talk, I outline the origins of the PTA foreground signals from the IISM, their consequences for gravitational-wave astronomy, and their uses in studying IISM structure and the pulsars themselves. I highlight some recent results from scintillation and pulsar timing studies that link the two fields, including a measurement of scattering by a pulsar bow shock and detections of extreme scattering events.