TeV signatures of compact UHECR accelerators

We study numerically particle acceleration by the electric field induced near the horizon of a rotating supermassive (M \sim 10^9-10^{10} M_{\odot}) black hole embedded in the magnetic field B. We find that acceleration of protons to energy E > 10^{20} eV is possible only at extreme values of M and B. We also find that the acceleration is very inefficient and is accompanied by a broad band MeV-TeV radiation whose total power exceeds at least by a factor of 1000 the total power emitted in ultra-high energy cosmic rays (UHECR). This implies that if O(10) nearby quasar remnants were sources of proton events with energy E > 10^{20} eV, then each quasar remnant would overshine e.g. the Crab nebula by more than two orders of magnitude in the TeV energy band. Recent TeV observations exclude this possibility. A model in which O(100) sources are situated at 100-1000 Mpc is not ruled out and can be experimentally tested by present TeV gamma-ray telescopes. Such a model can explain the observed UHECR flux at moderate energies E \sim (4-5) 10^{19} eV.Comment: Replaced with published versio

No evidence for gamma-ray halos around active galactic nuclei resulting from intergalactic magnetic fields

We analyze the gamma-ray halo around stacked AGNs reported in Ap.J.Lett., 2010, 722, L39. First, we show that the angular distribution of gamma-rays around the stacked AGNs is consistent with the angular distribution of the gamma-rays around the Crab pulsar, which is a point source for Fermi/LAT. This makes it unlikely that the halo is caused by an electromagnetic cascade of TeV photons in the intergalactic space. We then compare the angular distribution of gamma-rays around the stacked AGNs with the point-spread function (PSF) of Fermi/LAT and confirm the existence of an excess above the PSF. However, we demonstrate that the magnitude and the angular size of this effect is different for photons converted in the front and back parts of the Fermi/LAT instrument, and thus is an instrumental effect.Comment: accepted to A&

Ultra-High Energy Cosmic Ray production in the polar cap regions of black hole magnetospheres

We develop a model of ultra-high energy cosmic ray (UHECR) production via acceleration in a rotation-induced electric field in vacuum gaps in the magnetospheres of supermassive black holes (BH). We show that if the poloidal magnetic field near the BH horizon is misaligned with the BH rotation axis, charged particles, which initially spiral into the BH hole along the equatorial plane, penetrate into the regions above the BH "polar caps" and are ejected with high energies to infinity. We show that in such a model acceleration of protons near a BH of typical mass 3e8 solar masses is possible only if the magnetic field is almost aligned with the BH rotation axis. We find that the power of anisotropic electromagnetic emission from an UHECR source near a supermassive BH should be at least 10-100 times larger then UHECR power of the source. This implies that if the number of UHECR sources within the 100 Mpc sphere is ~100, the power of electromagnetic emission which accompanies proton acceleration in each source, $10^{42-43}$ erg/s, is comparable to the typical luminosities of active galactic nuclei (AGN) in the local Universe. We also explore the acceleration of heavy nuclei, for which the constraints on the electromagnetic luminosity and on the alignment of magnetic field in the gap are relaxed

Astrophysical Origins of Ultrahigh Energy Cosmic Rays

In the first part of this review we discuss the basic observational features at the end of the cosmic ray energy spectrum. We also present there the main characteristics of each of the experiments involved in the detection of these particles. We then briefly discuss the status of the chemical composition and the distribution of arrival directions of cosmic rays. After that, we examine the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin (GZK) cutoff, and discuss the level of confidence with which each experiment have detected particles beyond the GZK energy limit. In the second part of the review, we discuss astrophysical environments able to accelerate particles up to such high energies, including active galactic nuclei, large scale galactic wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding galaxies, and gamma ray burst fireballs. In the third part of the review we provide a brief summary of scenarios which try to explain the super-GZK events with the help of new physics beyond the standard model. In the last section, we give an overview on neutrino telescopes and existing limits on the energy spectrum and discuss some of the prospects for a new (multi-particle) astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used to probe new physics beyond the electroweak scale.Comment: Higher resolution version of Fig. 7 is available at http://www.angelfire.com/id/dtorres/down3.html. Solicited review article prepared for Reports on Progress in Physics, final versio

Time Structure of Ultra-High Energy Cosmic Ray Sources and Consequences for Multi-messenger Signatures.

The latest results on the sky distribution of ultra-high energy cosmic ray sources have consequences for their nature and time structure. If the sources accelerate predominantly nuclei of atomic number A and charge Z and emit continuously, their luminosity in cosmic rays above ~6x10^{19} eV can be no more than a fraction of ~5x10^{-4} Z^{-2} of their total power output. Such sources could produce a diffuse neutrino flux that gives rise to several events per year in neutrino telescopes of km^3 size. Continuously emitting sources should be easily visible in photons below ~100 GeV, but not in TeV gamma-rays which are likely absorbed within the source. For episodic sources that are beamed by a Lorentz factor Gamma, the bursts or flares have to last at least ~0.1 Gamma^{-4} A^{-4} yr. A considerable fraction of the flare luminosity could go into highest energy cosmic rays, in which case the rate of flares per source has to be less than ~5x10^{-3} Gamma^4 A^4 Z^2 yr^{-1}. Episodic sources should have detectable variability both at GLAST and TeV energies, but neutrino fluxes may be hard to detect.Comment: 6 pages, no figure