Millisecond pulsars phenomenology under the light of graph theory

¹ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Barcelona, Spain
² Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
³ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone (RM), Italy
⁴ Tor Vergata University of Rome, Via della Ricerca Scientifica 1, 00133 Roma, Italy
⁵ Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Rome, Italy
⁶ Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
⁷ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy

^★ Corresponding author; crodriguez@ice.csic.es

Received: 17 May 2024
Accepted: 16 October 2024

Abstract

We compute and apply the minimum spanning tree (MST) of the binary millisecond pulsar population, and discuss aspects of the known phenomenology of these systems in this context. We find that the MST effectively separates different classes of spider pulsars – eclipsing radio pulsars in tight binary systems with a companion of either ~0.1–0.8 M_⊙ (redbacks) or ≲0.06 M_⊙ in mass (black widows) – into distinct branches. The MST also separates black widows (BWs) in globular clusters from those found in the field and groups other pulsar classes of interest, including transitional millisecond pulsars (tMSPs). Using the MST and a defined ranking for similarity, we identify possible candidates likely to belong to these pulsar classes. In particular, based on this approach, we propose the BW classification of J1300+1240, J1630+3550, J1317−0157, J1221−0633, J1627+3219, J1737−0314A, and J1701−3006F, discuss that of J1908+2105, and analyze J1723−2837, J1431−4715, and J1902−5105 as possible transitional systems. We introduce an algorithm that quickly locates where new pulsars fall within the MST and use this to examine the positions of the TMSP IGR J18245−2452 (PSR J1824−2452I), the tMSP candidate 3FGL J1544.6−1125, and the accreting millisecond X-ray pulsar SAX J1808.4−3658. Assessing the positions of these sources in the MST – assuming a range for their unknown variables (e.g., the spin period derivative of PSR J1824−2452I) –, we can effectively narrow down the parameter space necessary for searching for and determining key pulsar parameters through targeted observations.