Profile changes associated with DM events in PSR J1713+0747

TL;DR

This study investigates profile variations in pulsar PSR J1713+0747 during dispersion measure events, finding correlated, achromatic profile changes that challenge simple lensing models and suggest more complex propagation effects.

Contribution

The paper provides evidence of transient, achromatic pulse profile variations associated with DM events, questioning the lensing interpretation and highlighting the need for higher resolution data.

Findings

Profile variations are correlated with DM events.

Variations are achromatic across multiple radio frequencies.

Results challenge simple lensing models of the interstellar medium.

Abstract

Propagation effects in the interstellar medium and intrinsic profile changes can cause variability in the timing of pulsars, which limits the accuracy of fundamental science done via pulsar timing. One of the best timing pulsars, PSR J1713+0747, has gone through two `dip' events in its dispersion measure (DM) time series. If these events reflect real changes in electron column density, they should lead to multiple imaging. We show that the events are are well fitted by an underdense corrugated sheet model, and look for associated variability in the pulse profile using principal component analysis. We find that there are transient pulse profile variations, but they vary in concert with the dispersion measure, unlike what is expected from lensing due to a corrugated sheet. The change is consistent in shape across profiles from both the Greenbank and Arecibo radio observatories, and its amplitude appears to be achromatic across the 820-MHz, 1.4-GHz, and 2.3-GHz bands, again unlike expected from interference between lensed images. This result is puzzling. We note that some of the predicted lensing effects would need higher time and frequency resolution data than used in this analysis. Future events appear likely, and storing baseband data or keeping multiple time-frequency resolutions will allow more in-depth study of propagation effects and hence improvements to pulsar timing accuracy.