Ultra-High Energy Cosmic Rays and Diffuse Photon Spectrum

It is argued that if extragalactic magnetic fields are smaller than 2x10^{-12} G the flux of ultra-high energy photons of (a few)x10^{-1} eV cm^{-2}s^{-1}sr^{-1} predicted in the top-down models of UHE CR implies similar flux of the diffuse photons in the energy range 10^{15}-10^{17} eV, which is close to the existing experimental limit.Comment: Talk given at XI Rencontres de Blois. 3 pages, no figure

Full sky harmonic analysis hints at large UHECR deflections

The full-sky multipole coefficients of the ultra-high energy cosmic ray (UHECR) flux have been measured for the first time by the Pierre Auger and Telescope Array collaborations using a joint data set with E > 10 EeV. We calculate these harmonic coefficients in the model where UHECR are protons and sources trace the local matter distribution, and compare our results with observations. We find that the expected power for low multipoles (dipole and quadrupole, in particular) is sytematically higher than in the data: the observed flux is too isotropic. We then investigate to which degree our predictions are influenced by UHECR deflections in the regular Galactic magnetic field (GMF). It turns out that the UHECR power spectrum coefficients $C_\ell$ are quite insensitive to the effects of the GMF, so it is unlikely that the discordance can be reconciled by tuning the GMF model. On the contrary, a sizeable fraction of uniformly distributed flux (representing for instance an admixture of heavy nuclei with considerably larger deflections) can bring simulations and observations to an accord.Comment: 8 pages, 4 figures and one table, JETPL style -- v2 as published in JETP

Star Wreck

Electroweak models with low-energy supersymmetry breaking predict the existence of stable non-topological solitons, Q-balls, that can be produced in the early universe. The relic Q-balls can accumulate inside a neutron star and gradually absorb the baryons into the scalar condensate. This causes a slow reduction in the mass of the star. When the mass reaches a critical value, the neutron star becomes unstable and explodes. The cataclysmic destruction of the distant neutron stars may be the origin of the gamma-ray bursts.Comment: 9 pages; references adde

GRB observations by Fermi LAT revisited: new candidates found

We search the Fermi-LAT photon database for an extended gamma-ray emission which could be associated with any of the 581 previously detected gamma-ray bursts (GRBs) visible to the Fermi-LAT. For this purpose we compare the number of photons with energies E > 100 MeV and E > 1 GeV which arrived in the first 1500 seconds after the burst from the same region, to the expected background. We require that the expected number of false detections does not exceed 0.05 for the entire search and find the high-energy emission in 19 bursts, four of which (GRB 081009, GRB 090720B, GRB 100911 and GRB 100728A) were previously unreported. The first three are detected at energies above 100 MeV, while the last one shows a statistically significant signal only above 1 GeV.Comment: Updated after referee comments, published in MNRAS Letters; 5 pages, 2 table

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&

Estimate of the correlation signal between cosmic rays and BL Lacs in future data

The existing correlation between BL Lacertae objects (BL Lacs) and cosmic-ray events observed by HiRes experiment provide sufficient information to formulate quantitatively the hypothesis about the flux of neutral cosmic-ray particles originated from BL Lacs. We determine the potential of future cosmic ray experiments to test this hypothesis by predicting the number of coincidences between arrival directions of cosmic rays and positions of BL Lacs on the celestial sphere, which should be observed in the future datasets. We find that the early Pierre Auger data will not have enough events to address this question. On the contrary, the final Pierre Auger data and the early Telescope Array data will be sufficient to fully test this hypothesis. If confirmed, it would imply the existence of highest-energy neutral particles coming from cosmological distances.Comment: 5 page

Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"

We argue that the data published by the Pierre Auger Collaboration (arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most of the highest-energy cosmic rays are protons from nearby astrophysical sources, either Active Galactic Nuclei or other objects with a similar spatial distribution.Comment: 1000 words, 2 figures, scicite.st

BL Lacertae are probable sources of the observed ultra-high energy cosmic rays

We calculate angular correlation function between ultra-high energy cosmic rays (UHECR) observed by Yakutsk and AGASA experiments, and most powerful BL Lacertae objects. We find significant correlations which correspond to the probability of statistical fluctuation less than $10^{-4}$, including penatly for selecting the subset of brightest BL Lacs. We conclude that some of BL Lacs are sources of the observed UHECR and present a list of most probable candidates.Comment: Replaced with the version accepted for publication in JETP Let