Gamma rays and neutrinos as complementary probes in astrophysics

Abstract

Electrons are more susceptible to energy losses in magnetic fields and photon fields than protons. Hence, photons at various wavelengths, including gamma rays, bring more readily information on high-energy electrons than on protons. Neutrinos provide a unique tracer for protons. Furthermore, at high energies the neutrino flux can considerably exceed the gamma-ray flux, as gamma rays above ~ 1 MeV are degraded by γ-γ interactions in compact high-intensity sources. Active galactic nuclei (AGN) with outputs > 1045 ergs s−1 and dimensions ~ 1014 cm would constitute such sources. If the AGN are powered by ultra-massive black holes, then these numerical conditions are satisfied, and at high energies the flux J ν > J γ. Berezinsky and Ginzburg have pointed out that the photon intensity around spinars is not sufficient to cause gamma-ray degradation. These authors have demonstrated that the measurement of neutrino flux, combined with the measurement (or upper limit) of gamma-ray flux would show whether the active galactic nuclei are powered by massive black holes or spinars. We estimate that gamma rays would be degraded at spinars, too, at energies > 1 GeV.