Probing intergalactic magnetic fields with simulations of electromagnetic cascades
Abstract
We determine the effect of intergalactic magnetic fields on the distribution of highenergy gamma rays by performing threedimensional Monte Carlo simulations of the development of gammarayinduced electromagnetic cascades in the magnetized intergalactic medium. We employ the socalled "Large Sphere Observer" method to efficiently simulate blazar gamma ray halos. We study magnetic fields with a Batchelor spectrum and with maximal left and righthanded 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 spirallike 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 quantitative way to infer the helicity of the intervening magnetic fields from the morphology of individual blazar halos for magnetic field strengths B ≳10^{15} G and magnetic coherence lengths L_{c}≳100 Mpc . We show that the S statistics has a better performance than the Q statistics when assessing magnetic helicity from the simulated halos.
 Publication:

Physical Review D
 Pub Date:
 October 2016
 DOI:
 10.1103/PhysRevD.94.083005
 arXiv:
 arXiv:1607.00320
 Bibcode:
 2016PhRvD..94h3005A
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 14 pages, 7 figures