Interstellar scintillation of PSR J0437-4715

Scattering of electromagnetic radiation from a pulsar by the interstellar medium results in the phenomena of pulse broadening and interstellar scintillation. The decorrelation bandwidth, scintillation time scale, and temporal broadening characterize these phenomena and provide information about the scattering material. Models of interstellar scattering predict how these observables should scale with frequency.; We present revised estimates of these quantities for PSR J0437-4715 and find that the scattering occurs at the surface of the Local Bubble. Our results, derived from interferometric observations at 330 MHz at two epochs using the Very Long Baseline Array (VLBA), do not scale with observing frequency as expected in comparison with previously reported measurements by other groups; however, we detect evidence of fine structure on frequency and time scales which appear to agree roughly with the earlier measurements. Misidentification of such fine structure for the scintillation pattern may explain the discrepancy between our results and those of the other groups and, furthermore, could explain the observed discontinuity in the scaling of temporal broadening with dispersion measure.