The multiple facets of millisecond pulsar binaries

TL;DR

Recent optical observations of millisecond pulsar binaries reveal diverse emission mechanisms and raise fundamental questions about pulsation universality, accretion effects, and wind interactions, requiring advanced high-time-resolution studies.

Contribution

This paper highlights the potential of future time domain astronomy facilities to systematically study optical pulsations across all MSP evolutionary stages.

Findings

Optical pulsations are detected in three MSP systems at different stages.

Emission mechanisms vary significantly across accretion regimes.

High-time-resolution observations are essential to understand pulsar and binary interactions.

Abstract

Millisecond pulsar (MSP) binaries are unique laboratories for studying matter and radiation under extreme conditions that are unattainable on Earth. Recent detections of optical millisecond pulsations from three systems in distinct evolutionary stages have opened an entirely new observational window to investigate particle acceleration, pulsar-disk interplay, and intrabinary wind interactions. These discoveries reveal unexpectedly diverse emission mechanisms across accretion regimes, with optical efficiencies in some systems far exceeding those predicted by rotation-powered models. Despite decades of research, key questions remain unresolved: are optical pulsations a universal property of MSPs? How does the presence of an accretion disk boost the conversion of spin-down power into coherent optical emission? What physical processes drive the observed fast variability, and how do pulsar and companion winds regulate mass transfer and binary evolution? Addressing these fundamental problems requires high-time-resolution optical observations, rapid-response observing capabilities, and time-resolved spectroscopy at moderate spectral resolution to map disk and intrabinary-shock variability. Future facilities dedicated to time domain astronomy present a unique opportunity to perform a systematic exploration of optical pulsars across all MSP evolutionary stages for the first time and answer the above-mentioned fundamental questions.