Assessing transitional pulsar candidates through a quantitative estimation of their light-curve similarity

Abstract

Transitional millisecond pulsars are often identified through X-ray light-curve morphology, especially by visual comparison with the prototype PSR J1023+0038. Such classifications remain qualitative and lack a calibrated notion of how much variability is already present within the prototype itself. We introduce a Dynamic Time Warping (DTW) framework that compares light curves through moving-window similarity distributions and calibrates candidate-prototype distances against the internal heterogeneity of PSR J1023+0038. In this formulation, a source is not simply asked to resemble one prototype observation, but to remain compatible with the range of morphologies exhibited by the prototype across observations. We apply the method to confirmed and candidate tMSPs and to a control sample of non-tMSP systems. The resulting similarity measure provides a reproducible ranking for tMSP-like behaviour and is therefore useful for candidate triage and archival searches. At the same time, the control sample shows that short-timescale accretion variability can partly mimic tMSP-like morphology, demonstrating that light-curve shape alone is a screening diagnostic rather than a definitive class identifier.