Effects of Intermittent Emission: Noise Inventory for Scintillating Pulsar B0834+06

TL;DR

This study analyzes how intermittent pulsar emission influences noise characteristics in observations, revealing that flux variations significantly affect self-noise and that intermittency impacts pulsar timing and astrometry accuracy.

Contribution

It introduces a detailed analysis of noise behavior in pulsar observations, highlighting the role of intermittency and flux variations in self-noise and secondary spectrum features.

Findings

Self-noise is about 3 times higher than expected for constant flux.

Intermittent emission concentrates self-noise near the origin in the secondary spectrum.

Intermittency limits pulsar astrometry and timing precision.

Abstract

We compare signal and noise for observations of the scintillating pulsar B0834+06, using very-long baseline interferometry and a single-dish spectrometer. Comparisons between instruments and with models suggest that amplitude variations of the pulsar strongly affect the amount and distribution of self-noise. We show that noise follows a quadratic polynomial with flux density, in spectral observations. Constant coefficients, indicative of background noise, agree well with expectation; whereas second-order coefficients, indicative of self-noise, are about 3 times values expected for a pulsar with constant on-pulse flux density. We show that variations in flux density during the 10-sec integration account for the discrepancy. In the secondary spectrum, about 97% of spectral power lies within the pulsar's typical scintillation bandwidth and timescale; an extended scintillation arc contains about 3%. For a pulsar with constant on-pulse flux density, noise in the dynamic spectrum will appear as a uniformly-distributed background in the secondary spectrum. We find that this uniform noise background contains 95% of noise in the dynamic spectrum for interferometric observations; but only 35% of noise in the dynamic spectrum for single-dish observations. Receiver and sky dominate noise for our interferometric observations, whereas self-noise dominates for single-dish. We suggest that intermittent emission by the pulsar, on timescales < 300 microseconds, concentrates self-noise near the origin in the secondary spectrum, by correlating noise over the dynamic spectrum. We suggest that intermittency sets fundamental limits on pulsar astrometry or timing. Accounting of noise may provide means for detection of intermittent sources, when effects of propagation are unknown or impractical to invert.