New technique for determining a pulsar period: Waterfall principal component analysis

¹ University of Padova, Department of Physics and Astronomy “Galileo Galilei”, Via Marzolo, 8, 35131 Padova PD, Italy
e-mail: giampiero.naletto@unipd.it
² Department of Electrical Engineering, Universidad de Chile, Av. Tupper 2007, Santiago 8370451, Chile
e-mail: tcassanelli@ing.uchile.cl
³ INAF Astronomical Observatory of Padova, Vicolo dell’Osservatorio, 5, 35122 Padova, Italy
⁴ University of Padova, Department of Information Engineering, Via Gradenigo, 6/A, 35131 Padova PD, Italy
⁵ Trento Institute for Fundamental Physics and Applications, Via Sommarive, 14 38123 Povo TN, Italy

Received: 10 March 2022
Accepted: 27 April 2022

Abstract

Aims. This paper describes a new technique for determining the optimal period of a pulsar and consequently its light curve.

Methods. The implemented technique makes use of the principal component analysis (PCA) applied to the so-called waterfall diagram, which is a bidimensional representation of the acquired data of the pulsar. In this context, we have developed the python package pywpf to easily retrieve the period with the presented method.

Results. We applied this technique to sets of data of the brightest pulsars in visible light that we obtained with the fast photon counter Iqueye. Our results are compared with those obtained by different and more classical analyses (e.g., epoch folding), showing that the periods so determined agree within the errors, and that the errors associated with the waterfall-PCA folding technique are slightly smaller than those obtained by the x² epoch-folding technique. We also simulated extremely noisy situations, showing that by means of a new merit function associated with the waterfall-PCA folding, it is possible to become more confident about the determined period with respect to the x² epoch-folding technique.