A Multi-Frequency Scintillation Arc Study of Pulsar B1133+16*

The arrival times of pulsar 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 time-variable delays in the interstellar medium. We investigate interstellar delays using 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 almost two decades ago, the structures that cause them are still unknown. There is accumulating evidence that the scattering from many pulsars is extremely anisotropic resulting in highly elongated, linear brightness functions. We present a three-frequency Arecibo study of scintillation arcs from one nearby, bright, high-velocity pulsar, B1133+16. We show that a one-dimensional, linear brightness function is in good agreement with the data at all three observing frequencies. Using two separate methods we find that the broadening of the arc is less frequency-dependent than expected by standard scattering theory. Our results place the scattering screen at a distance that is broadly consistent with an origin at the boundary of the Local Bubble.