Axion-photon Multimessenger Astronomy with Giant Flares

We treat prospects for multimessenger astronomy with giant flares (GFs), a rare transient event featured by magnetars that can be as luminous as a hundred of the brightest supernovae ever observed. The beamed photons could correlate with an axion counterpart via resonant conversion in the magnetosphere. In a realistic parameter space, we find that the sensitivity limit to Galactic GFs for currently viable experiments is g(phi gamma) > several x 10(-13) GeV-1 and g(phi e) > few x 10(-12). We rule out the compatibility of axion flares with the recent XENON1T excess only due to the time persistence of the signal.