Spiders in the Optical Regime

Abstract

Spider pulsars pair a millisecond pulsar with a low-mass companion heavily ablated by its coun- terpart. Pulsar timing provides the system’s orbital period and mass function. Optical photometry of their distinctive sinusoidal light curves then constrains the orbital inclination. The companion’s projected radial velocity amplitude can also be constrained through the Doppler shift of lines in its optical spectra. With these three elements the binary mass function can be solved, and pulsar masses estimated in spider systems. Pulsar mass measurements in spider systems hold high poten- tial to constrain the maximum pulsar mass, and thus the neutron star equation of state. The ultimate aim of this work is to marry the photometric and spectroscopic aspects of optical modelling in a self-consistent manner. To this end, four spider systems are modelled with Icarus Firstly, the discovery and modelling of PSR J1910−5320 is presented. Here a novel RV curve modelling technique is debuted. This produces model RV curves simultaneously alongside the standard Icarus photometric model, ensuring self-consistency. This constrains the RV in the system and thus the pulsar mass to good precision. A potentially ‘super-massive’ (> 2𝑀⊙ ) neutron star, PSR J1810+1744 is then modelled. Here the novel RV curve fitting of the previous chapter is generalised to work with raw observed spec- troscopy, rather than RV curves. This technique is also benchmarked against a similar, but much more computationally expensive, spectroscopic modelling technique. The precision of the new technique does not reach that of the more exhaustive modelling, but it produces accurate results that reproduce the observed velocity information. Tentative lower limits are placed on the pulsar mass, suggesting it is indeed ‘super-massive’ Finally, two redback spider pulsars recently discovered with MeerKAT are modelled. Here in- creasing levels of constraint on the RV are tested, modelling previously published RV curves with the novel RV curve modelling presented here. The system parameters are well characterised by the modelling performed, with particularly precise mass constraints obtained. PSR J2333−5526 is constrained to be 2.28+0.07 𝑀 , with independent inclination limits ensuring a minimum pulsar −0.06 ⊙ mass of 1.98𝑀⊙ . Modelling of PSR J0955−3947 also highlights the need for the RV curves of specific spectral lines when targeting constraint of the centre-of-light correction. A moderate pulsar mass estimate of 1.53 ± 0.05𝑀⊙ is also produced.

Date of Award	1 Aug 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Keith (Supervisor) & Rene Breton (Supervisor)