(Prof Paula M. Chadwick, Dr Anthony M. Brown)
The axion is a solution for the strong CP problem and a plausible dark matter candidate. Axions may be produced by nucleon-nucleon Bremsstrahlung processes within pulsars and then subsequently decay to gamma-rays. We determine upper-limits (ULs) for such gamma-ray emission from 18 nearby gamma-ray dark pulsars using 9 years of Pass 8 Fermi-LAT event data. We then use these ULs in conjunction with the astrophysical model of Berenji et al (2016) to set an improved yet conservative upper bound on axion mass. Finally we briefly consider the axion mass that would result from an alternative axion luminosity model of Raffelt (1996) and highlight the need for characterising the axion to photon interconversion in B field regime of pulsars.