Noise and Signal for Spectra of Intermittent Noiselike Emission

TL;DR

This paper investigates how intermittency in noiselike signals, such as pulsars, combined with propagation effects, influences the noise distribution in observed spectra and correlation functions, revealing concentration effects near the central lag.

Contribution

It provides a mathematical framework for understanding how intermittency and propagation affect noise distribution in spectra and correlation functions of noiselike sources.

Findings

Intermittency concentrates noise near the central lag of the correlation function.

Propagation effects leave the average spectrum and noise distribution among channels unchanged.

Mathematical expressions relate the time envelope and propagation kernel to noise distribution.

Abstract

We show that intermittency of noiselike emission, after propagation through a scattering medium, affects the distribution of noise in the observed correlation function. Intermittency also affects correlation of noise among channels of the spectrum, but leaves the average spectrum, average correlation function, and distribution of noise among channels of the spectrum unchanged. Pulsars are examples of such sources: intermittent and affected by interstellar propagation. We assume that the source emits Gaussian white noise, modulated by a time-envelope. Propagation convolves the resulting time series with an impulse-response function that represents effects of dispersion, scattering, and absorption. We assume that this propagation kernel is shorter than the time for an observer to accumulate a single spectrum. We show that rapidly-varying intermittent emission tends to concentrate noise near the central lag of the correlation function. We derive mathematical expressions for this effect, in terms of the time envelope and the propagation kernel. We present examples, discuss effects of background noise, and compare our results with observations.