The frequency dependence of radio pulse arrival times provides a probe of structures in the intervening media. Demorest et al. was the first to show a short-term (similar to 100-200 days) reduction in the electron content along the line of sight to PSR. J1713+0747 in data from 2008 (approximately MJD 54750) based on an apparent dip in the dispersion measure of the pulsar. We report on a similar event in 2016 (approximately MJD 57510), with average residual pulse-arrival times approximate to-3.0, -1.3, and -0.7 mu s at 820, 1400, and 2300. MHz, respectively. Timing analyses indicate possible departures from the standard v(-2) dispersive-delay dependence. We discuss and rule out a wide variety of potential interpretations. We find the likeliest scenario to be lensing of the radio emission by some structure in the interstellar medium, which causes multiple frequency-dependent pulse arrival-time delays.
Title
A second chromatic timing event of interstellar origin toward PSR J1713+0747
Lam, M. T., et al. (2018 July) "A second chromatic timing event of interstellar origin toward PSR J1713+0747." Astrophysical Journal 861 (2): Article 132.