The maximum energy and spectra of cosmic rays accelerated in active galactic nuclei

Abstract

Abstract. We computed the energy spectra of the incident (on an air shower array) ultrahighenergy (E > 4⋅10 19 eV) cosmic rays (CRs) that were accelerated in nearby Seyfert nuclei at redshifts z≤ 0.0092 and in BL Lac objects. These were identified as possible CR sources in our previous works. For our calculations, we took the distribution of these sources over the sky from catalogs of active galactic nuclei. In accordance with the possible particle acceleration mechanisms, the initial CR spectrum was assumed to be monoenergetic for BL Lac objects and a power law for Seyfert nuclei. The CR energy losses in intergalactic space were computed by the Monte Carlo method. We considered the losses through photopion reactions with background radiation and the adiabatic losses. The artificial proton statistic was 10 5 for each case considered.The maximum energy of the CRs incident on an external air shower (EAS) array was found to be 10 21 eV, irrespective of where they were accelerated. The computed spectra of the particles incident on an EAS array agree with the measurements, which indirectly confirms the adopted acceleration models. At energies E≥10 20 eV, the spectrum of the protons from nearby Seyfert nuclei that reached an EAS array closely matches the spectrum of the particles from BL Lac objects. BL Lac objects are, on average, several hundred Mpc away. Therefore, it is hard to tell whether a blackbody cutoff exists or not by analyzing the shape of the measured spectrum at E≥ 5⋅10 19 eV.

Study of cosmic ray sources using data on extragalactic diffuse gamma-ray emission

“…In this work we consider possible specific type of AGNs in which supermassive black hole is surrounded by a super strong magnetic field of 10 10 -10 11 Gs. Particles are accelerated there to ultra-high energies [9][10][11][12]. Here we show that these AGNs contribute negligibly to the UHECR flux at the Earth.…”

Cosmic ray contribution in extragalactic background gamma-ray emission at an energy of 0.1 TeV

“…The cross section of the ICS at E e > E t equals (4) and equals the Thomson cross section, σ T ≈ 6.65· 10 −25 cm 2 , at E e < E t . For electrons or quanta at lower energies, E e < E t , there is no PP, and comparatively soft quanta are produced in ICS, at mean energies…”

“…The ICS is considered in the same way using Eqs. (4,5). The electron is treated until its energy decreases to 10 14 eV (as at lower energies it loses energy fairly slowly scattering soft quanta).…”

“…To describe UHECR energy spectra measured at the Earth the particle spectrum in Bl Lacs is either monoenergetic with energy E = 10 21 eV or exponential with the index in the range 2-3; in Seyfert nuclei the CR spectrum is exponential with the index in the range 2-3. Particles in sources are accelerated to the energy not higher than 10 21 eV [3,4].…”

“…Experimental data obtained with CR giant arrays -Pierre Auger Observatory and Telescope Array -indicate that the UHECR energy spectrum is suppressed. However, there may be another reason for spectrum suppression besides the GZK-effect: particles are accelerated to the maximum energy of approximately 10 21 eV due to conditions in possible UHECR sources [3,4]. As sources are still unknown, the acceleration energy limit cannot be ruled out.…”