Wavelet Denoising of Radio Observations of Rotating Radio Transients (RRATs): Improved Timing Parameters for Eight RRATs

Abstract

Rotating radio transients (RRATs) are sporadically emitting pulsars detectable only through searches for single pulses. While over 100 RRATs have been detected, only a small fraction (roughly 20%) have phase-connected timing solutions, which are critical for determining how they relate to other neutron star populations. Detecting more pulses in order to achieve solutions is a key to understanding their physical nature. Astronomical signals collected by radio telescopes contain noise from many sources, making the detection of weak pulses difficult. Applying a denoising method to raw time series prior to performing a single-pulse search typically leads to a more accurate estimation of their times of arrival (TOAs). Taking into account some features of RRAT pulses and noise, we present a denoising method based on wavelet data analysis, an image-processing technique. Assuming that the spin period of an RRAT is known, we estimate the frequency spectrum components contributing to the composition of RRAT pulses. This allows us to suppress the noise, which contributes to other frequencies. We apply the wavelet denoising method including selective wavelet reconstruction and wavelet shrinkage to the de-dispersed time series of eight RRATs with existing timing solutions. The signal-to-noise ratio (S/N) of most pulses are improved after wavelet denoising. Compared to the conventional approach, we measure 12% to 69% more TOAs for the eight RRATs. The new timing solutions for the eight RRATs show 16% to 90% smaller estimation error of most parameters. Thus, we conclude that wavelet analysis is an effective tool for denoising RRATs signal.

Evolution of Spin Period and Magnetic Field of the Crab Pulsar: Decay of the Braking Index by the Particle Wind Flow Torque

“…Wavelet analysis is a powerful time-frequency analysis method, like Fourier transform, which is particularly suitable for processing unstable signals such as complex noise or sudden changes in the data. Although this method is effective and has been applied in some fields of astronomy such as white dwarf [83] and pulsar [84,85], it has not yet been widely used in pulsar data processing from our knowledge. Perhaps the method of wavelet analysis will be helpful for the measurement of a braking index in the future [84].…”

“…Although this method is effective and has been applied in some fields of astronomy such as white dwarf [83] and pulsar [84,85], it has not yet been widely used in pulsar data processing from our knowledge. Perhaps the method of wavelet analysis will be helpful for the measurement of a braking index in the future [84]. Furthermore, due to the James Webb Space Telescope having been successfully launched and operated [86], more details of the Crab nebula will be discovered and analyzed.…”

DM-Free Curvelet Based Denoising for Astronomical Single Pulse Detection

“…It is effective for suppressing the terrestrial interference. Jiang et al [15] presented a wavelet based denoised approach for the de-dispersed time series which is utilized before the single-pulse search. Based on the a priori knowledge of the spin period of RRATs, they applied wavelet reconstruction and shrinkage to the selective frequency bands.…”

Radio Properties of Rotating Radio Transients: Single Pulse Spectral and Wait Time Analyses

“…Weak pulse analyses have been performed for RRATs (e.g. Cui et al 2017;Jiang et al 2017) and recent work by Bhattacharyya et al (2018) has found that PSR J1913+1330 exhibits a weak mode emission followed by long periods where there is no detectable emission. A lack of bright pulses could explain why our pulse wait-time distribution appears to support purely random emission, and does not show the secondary component seen in PSR J1819−1458 and PSR J1317−5759.…”