Testing the Production of Scintillation Arcs with the Pulsar B1133+16

Pulsars are extremely dense, highly magnetized stars that emit pulses of radio emission every millisecond or so. The arrival times of their radio signals at Earth observatories can be used as a clock precise enough to detect gravitational waves. Performing such a detection requires the mitigation of interference effects from the interstellar medium: the slightly ionized, mostly hydrogen gas that the radio waves traverse as they travel from the pulsar to Earth. We investigate radio wave delays using a powerful tool: scintillation arcs, fluctuations in frequency and time of the pulsar signal intensity that are manifested as parabolic arcs in the pulsar’s secondary spectrum. While scintillation arcs were first observed by Oberlin students almost two decades ago, the structures that cause them are still unknown. We explore the unique capabilities of the pulsar B1133+16 for testing models of scintillation arcs. Using measurements of scintillation arc curvatures over 96 days, we test a model for the annual modulation of arc curvature due to Earth’s orbit. The formalism for determining the width of a pulsar image from a scintillation arc width is used to design an empirical test of scintillation arc models based on the frequency dependence of arc widths. This formalism is then explored in the framework of a simple, one-dimensional model for the production of scintillation arcs