Bounding the Photon Mass With Pulsar Timing Observation Data From Multi‐Telescopes

We derive conservative upper limits on the photon rest mass from multi‐telescope pulsar timing data using a second‐order dispersion framework that accounts for both plasma and photon mass effects. Published uncertainties (, ) are treated as proxies for the maximum unmodeled delay, justified because such a delay cannot be fully absorbed by standard DM fitting and would inflate the reported errors. The most stringent nominal limit is from Long Wavelength Array observations of PSR B1133 + 16 at 26–88 MHz, although interstellar scattering at such low frequencies makes this an optimistic estimate; a robust, scattering‐free bound of is obtained from Parkes UWL data. Our comparative analysis confirms that low‐frequency coverage is the dominant factor for tightening pulsar‐based constraints, outweighing timing precision. The conservative methodology, validated by Monte Carlo simulations showing that injected delays produce residual rms consistent with reported , provides a robust foundation for future improvements with next‐generation telescopes and explicit fitting.