A Second Chromatic Timing Event of Interstellar Origin toward PSR J1713+0747

TL;DR

This paper reports a second interstellar event affecting pulsar timing, suggesting lensing effects in the interstellar medium cause frequency-dependent delays, which could impact pulsar timing precision.

Contribution

It documents a new interstellar timing event toward PSR J1713+0747 and proposes lensing as the likely cause, expanding understanding of interstellar medium effects.

Findings

Detected a second chromatic timing event in 2016.

Observed departures from standard dispersive delay models.

Lensing by interstellar structures likely causes the observed delays.

Abstract

The frequency dependence of radio pulse arrival times provides a probe of structures in the intervening media. Demorest et al. 2013 was the first to show a short-term (~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 of approximately 3.0,-1.3, and -0.7 microseconds at 820, 1400, and 2300 MHz, respectively. Timing analyses indicate possible departures from the standard nu^-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.