Three New Likely Spider Millisecond Pulsar Binaries and Optical Kinematic Tracers of Intrabinary Shocks

Jay Strader; Rebecca Kyer; Laura Chomiuk; Elias Aydi; Peter Craig; Thomas M. Do; Isabella Molina; Teresa Panurach; Subhroja Roy; Kirill V. Sokolovsky; Samuel J. Swihart; Ryan Urquhart

arXiv · 2610.00455

Three New Likely Spider Millisecond Pulsar Binaries and Optical Kinematic Tracers of Intrabinary Shocks

Jay Strader·Rebecca Kyer·Laura Chomiuk·Elias Aydi·Peter Craig·Thomas M. Do·Isabella Molina·Teresa Panurach·Subhroja Roy·Kirill V. Sokolovsky·Samuel J. Swihart·Ryan Urquhart

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Abstract

We report the discovery of three candidate spider millisecond pulsars via multi-wavelength follow-up of unassociated Fermi Large Area Telescope gamma-ray sources. All have optical spectroscopy from the SOAR 4.1-m telescope and X-ray data from Swift. Two optical/X-ray sources are exceptionally strong redback candidates, sitting close to the centres of the localization ellipses of the gamma-ray sources 4FGL J1020.4-5314 and 4FGL J1408.7-3747. We show that both optical sources are spectroscopic binaries with orbital periods (0.15-0.3 d) and mass functions (0.6-0.9 Msun) typical for redbacks. 4FGL J1020.4-5314 shows bright, very broad (full width at half maximum 2100 km/s) H-alpha emission in all spectra obtained over two years. Remarkably, the H-alpha radial velocities are offset in phase from the absorption-line velocities of the secondary, and match the signal expected for an emission source near the primary. This demonstrates, for the first time for any spider, that the H-alpha emission can be associated with an intrabinary shock that wraps around the pulsar, opening up the possibility of using optical emission lines as kinematic tracers of the intrabinary shock in some redbacks. A third candidate spider is less secure in its association with the gamma-ray source 4FGL J1429.8-0739, but has unusual properties, including a 30.5-hour orbital period, a potential subgiant secondary, and a high X-ray luminosity, making it worthy of further investigation.

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Jay Strader, Rebecca Kyer, Laura Chomiuk, Elias Aydi, Peter Craig, Thomas M. Do, Isabella Molina, Teresa Panurach, Subhroja Roy, Kirill V. Sokolovsky, Samuel J. Swihart, Ryan Urquhart. 2026-09-30. Three New Likely Spider Millisecond Pulsar Binaries and Optical Kinematic Tracers of Intrabinary Shocks. https://arxiv.org/abs/2610.00455

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