Applying clock comparison methods to pulsar timing observations

Siyuan Chen,François Vernotte,Enrico Rubiola

doi:10.1093/mnras/stab742

Abstract

ABSTRACT Frequency metrology outperforms any other branch of metrology in accuracy (parts in 10−16) and small fluctuations (&lt;10−17). In turn, among celestial bodies, the rotation speed of millisecond pulsars is by far the most stable (&lt;10−18). Therefore, the precise measurement of the time of arrival (TOA) of pulsar signals is expected to disclose information about cosmological phenomena, and to enlarge our astrophysical knowledge. Related to this topic, Pulsar Timing Array projects have been developed and operated for the last decades. The TOAs from a pulsar can be affected by local emission and environmental effects, in the direction of the propagation through the interstellar medium or universally by gravitational waves from super massive black hole binaries. These effects (signals) can manifest as a low-frequency fluctuation over time, phenomenologically similar to a red noise, while the remaining pulsar intrinsic and instrumental background (noise) are white. This article focuses on the frequency metrology of pulsars. From our standpoint, the pulsar is an accurate clock, to be measured simultaneously with several telescopes in order to reject the uncorrelated white noise. We apply the modern statistical methods of time-and-frequency metrology to simulated pulsar data, and we show the detection limit of the correlated red noise signal between telescopes.

Highlights

Millisecond pulsars (MSP) are considered extremely stable astronomical clocks because of their high energy and momentum in a small size (Verbiest et al 2009), albeit the observations can be affected by large observational white noise
On the other hand, red noise could originate from the MSP, the propagation through the interstellar medium or from gravitational waves (GWs) on the line of sight, it is common to all the RTs (Hellings & Downs 1983; Jenet & Romano 2015)
To ensure that our results are statistically robust, each of the three cases is based on 100 different realization sets and doing the analysis using all the clock comparison methods and the standard PTA/LEAP statistical limit (LSL) comparisons

Summary

Introduction

Millisecond pulsars (MSP) are considered extremely stable astronomical clocks because of their high energy and momentum in a small size (Verbiest et al 2009), albeit the observations can be affected by large observational white noise. Such noise can be due to the low signal-to-noise ratio of the MSP observations, and depends on the radio telescope (RT). The most interesting and likely to be detected source is a cosmic population of super massive black hole binaries (Taylor et al 2016 and Perrodin & Sesana 2018 for a recent review), whose interaction with the MSP signals introduces a correlated red noise in the time of arrival (TOA) series, with a phase power spectral density (PSD) proportional to 1/f13/3

Methods

Results

Conclusion