Gravitational lensing time delays with massive photons

TL;DR

This paper explores how gravitational lensing time delays can be used to set limits on the photon mass, analyzing different lens models and using observational data from AGN to derive constraints.

Contribution

It provides explicit formulas for time delays with massive photons in Schwarzschild and isothermal lenses and demonstrates how these delays can constrain photon mass.

Findings

Time delays are insensitive to photon mass in isothermal lenses.

Black hole mass influences photon mass-dependent time delays.

Observational data yields photon mass bounds comparable to solar radio wave deflection limits.

Abstract

This paper investigates the use of gravitational time delays of macro-lenses to constrain a possible photon mass. The time delay between the 2 compact images of a source of massive photons is computed. Explicit expressions are given for Schwarzschild and singular isothermal lenses. In the latter case, the time delay is very insensitive to the photon mass. Modeling lens galaxies by a singular isothermal model and a central supermassive black hole, the photon mass-dependent part of the time delay between the compact images is shown to be proportional to the mass of the black hole. The sensitivity of time delays to the photon mass is illustrated by a bound obtained from 3 AGN which have measurements in several passbands. The bound obtained is comparable to the limit with the deflection of radio waves by the Sun.