We determine the effect of intergalactic magnetic fields on the distribution of high energy gamma rays by performing three-dimensional Monte Carlo simulations of the development of gamma-ray-induced electromagnetic cascades in the magnetized intergalactic medium .
We employ the so-called “ Large Sphere Observer ” method to efficiently simulate blazar gamma ray halos .
We study magnetic fields with a Batchelor spectrum and with maximal left- and right-handed helicities .
We also consider the case of sources whose jets are tilted with respect to the line of sight .
We verify the formation of extended gamma ray halos around the source direction , and observe spiral-like patterns if the magnetic field is helical .
We apply the Q -statistics to the simulated halos to extract their spiral nature and also propose an alternative method , the S -statistics .
Both methods provide a quantative way to infer the helicity of the intervening magnetic fields from the morphology of individual blazar halos for magnetic field strengths B \gtrsim 10 ^ { -15 } { G } and magnetic coherence lengths L _ { c } \gtrsim 100 { Mpc } .
We show that the S -statistics has a better performance than the Q -statistics when assessing magnetic helicity from the simulated halos .