Probing the Intergalactic Magnetic Fields by means of high-energy pair halos around extreme blazars
by
PAOLO DA VELA(SI)
→
Europe/Rome
131 (INFN edificio C)
131
INFN edificio C
Description
The origin of cosmic magnetic fields permeating galaxies and clusters is still unknown. To undertstand the origin and the evolution of the primordial cosmic magnetic fields we need to probe the existence and to characterize magnitude and correlation length of magnetic field in voids (Intergalactic magnetic field, IGMF), where pollution from magnetic fields associated to structures is expected to be minimal. Techniques like Faraday Rotation and Zeeman splitting permit to compute upper limits on IGMF of the order of 10^-9 G.
Nevertheless our knowledge on IGMF is still poor.
Very High Energy (VHE) photons (E>50 GeV) coming from extreme Blazars interact with Optical/Infrared Extragalactic Background Light (EBL). Because of these interactions electron-positron pairs are produced. These, in turn, upscatter via inverse Compton the CMB photons producing a reprocessed emission. If the primary photons have energies higher than 10 TeV this component will be in the GeV domain. IGMF deflects the pairs so this component will be in the form of extended emission whose angular extension depends on the strength of IGMF. The detection of this component is an unique tool to measure the IGMF.
The measurement of halo emission by Cherenkov telescopes like MAGIC depends strictly on its capability to disentangle the extended from the point-like emission of the source. For the first time the detailed characterization of the Point Spread Function (PSF) of MAGIC has allowed to assess the possibility to reveal the extended emission due to IGMF. The emission profiles of different blazars have been compared with the MAGIC PSF, without finding significant deviations from the point-like behavior. As a result we computed upper limits on the extended emission assuming different models for halo emission.