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Ultra-high energy cosmic rays
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Title: What IceCube neutrinos teach us about the GRB location
Author: Maria Petropoulou, Dimitrios Giannios, Stavros Dimitrakoudis

The recent discovery of extragalactic PeV neutrinos opens a new window to the exploration of cosmic-ray accelerators. The observed PeV neutrino flux is close to the Waxman-Bahcall upper bound implying that gamma-ray bursts (GRBs) may be the source of ultra-high energy cosmic rays (UHECRs). Starting with the assumption of the GRB-UHECR connection, we show using both analytical estimates and numerical simulations that the observed neutrinos can originate at the jet as a result of photopion interactions with the following implications: the neutrino spectra are predicted to have a cutoff at energy \simless 10~PeV; the dissipation responsible for the GRB emission and cosmic-ray acceleration takes place at distances 
diss \simeq 3 x 10^{11}-3 x 10^{13}~cm from the central engine; the Thomson optical depth at the dissipation region is \tau_t~1; the jet carries a substantial fraction of its energy in the form of Poynting flux at the dissipation region, and has a Lorentz factor Gamma \simeq 100-500.

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Cosmic rays: Fermi telescope settles mystery of origin

Scientists have conclusive proof that many cosmic rays raining down on Earth come from distant exploded stars.
Nasa's Fermi telescope was used to study the very distinctive light that is produced when these protons crash into other particles in space.

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Ultra-high Energy Cosmic Rays
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Title: Chandra observations and classification of AGN-candidates correlated with Auger UHECRs
Authors: William A. Terrano, Ingyin Zaw, Glennys R. Farrar

We report on Chandra X-ray observations of possible-AGNs which have been correlated with Ultra-high Energy Cosmic Rays (UHECRs) observed by the Pierre Auger Collaboration. Combining our X-ray observations with optical observations, we conclude that one-third of the 21 Veron-Cetty Veron (VCV) galaxies correlating with UHECRs in the first Auger data-release are actually not AGNs. We review existing optical observations of the 20 VCV galaxies correlating with UHECRs in the second Auger data-release and determine that three of them are not AGNs and two are uncertain. Overall, of the 57 published UHECRs with |b|>10 degrees, 22 or 23 correlate with true AGNs using the Auger correlation parameters. We also measured the X-ray luminosity of ESO139-G12 to complete the determination of the bolometric luminosities of AGNs correlating with UHECRs in the first data-set. Apart from two candidate sources which require further observation, we determined bolometric luminosities for the candidate galaxies of the second dataset. We find that only two of the total of 69 published UHECRs correlate with AGNs (IC5135 and IC4329a) which are powerful enough in their steady-state to accelerate protons to the observed energies of their correlated UHECRs. The GZK expectation is that about 45% of the sources of UHECRs above 60 EeV should be contained within the z<0.018 volume defined by the Auger scan analysis, so an observed level of 30-50% correlation with weak AGNs is compatible with the suggestion that AGNs experience transient high-luminosity states during which they accelerate UHECRs.

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Ultra high energy cosmic rays
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 Neutrino no-show deepens cosmic ray mystery

GRBs, thought to occur when massive stars collapse to form black holes, could spew out ultra high energy cosmic rays (UHECRS). If they do, the UHECRs should interact with the photons also streaming out of the explosion to form neutrinos with energies in the hundreds of tera-electronvolts. These should then arrive on Earth along with the photons.
With this chain of events in mind, IceCube has been looking for neutrinos occurring at the same time as GRBs. From May 2009 to May 2010, gamma-ray satellite observatories saw 190 GRBs. Theory predicts that IceCube should have seen a handful of neutrinos at the same time, from the same region of the sky. But today IceCube reports that it saw absolutely nothing - a serious blow to a cascade of processes astrophysicists thought they understood.

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Ultra-high-energy cosmic rays
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Title: Newly-born pulsars as sources of ultrahigh energy cosmic rays
Authors: Ke Fang, Kumiko Kotera, Angela V. Olinto

Newly-born pulsars offer favourable sites for the injection of heavy nuclei, and for their further acceleration to ultrahigh energies. Once accelerated in the pulsar wind, nuclei have to escape from the surrounding supernova envelope. We examine this escape analytically and numerically, and discuss the pulsar source scenario in light of the latest ultrahigh energy cosmic ray (UHECR) data. Our calculations show that, at early times, when protons can be accelerated to energies E>10^20 eV, the young supernova shell tends to prevent their escape. In contrast, because of their higher charge, iron-peaked nuclei are still accelerated to the highest observed energies at later times, when the envelope has become thin enough to allow their escape. Ultrahigh energy iron nuclei escape newly-born pulsars with millisecond periods and dipole magnetic fields of ~10^(12-13) G, embedded in core-collapse supernovae. Due to the production of secondary nucleons, the envelope crossing leads to a transition of composition from light to heavy elements at a few EeV, as observed by the Auger Observatory. The escape also results in a softer spectral slope than that initially injected via unipolar induction, which allows for a good fit to the observed UHECR spectrum. We conclude that the acceleration of iron-peaked elements in a reasonably small fraction (< 0.01%) of extragalactic rotation-powered young pulsars would reproduce satisfactorily the current UHECR data. Possible signatures of this scenario are also discussed.

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NASA's Fermi Space Telescope Explores New Energy Extremes

614835main1_Fermi-3-year-226.jpg

After more than three years in space, NASA's Fermi Gamma-ray Space Telescope is extending its view of the high-energy sky into a largely unexplored electromagnetic range. Today, the Fermi team announced its first census of energy sources in this new realm.
Fermi's Large Area Telescope (LAT) scans the entire sky every three hours, continually deepening its portrait of the sky in gamma rays, the most energetic form of light. While the energy of visible light falls between about 2 and 3 electron volts, the LAT detects gamma rays with energies ranging from 20 million to more than 300 billion electron volts (GeV).

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Title: A Cocoon of Freshly Accelerated Cosmic Rays Detected by Fermi in the Cygnus Superbubble
Authors: Ackermann M., Ajello M., Allafort A., Baldini L., Ballet J., Barbiellini G., Bastieri D., Belfiore A., Bellazzini R., Berenji B., Blandford R. D., Bruel P., Casandjian J. M., COHEN-TANUGI J., Dumora D., Fegan S. J., Fortin P., Grenier I. A., Knödlseder J., Lott B., MEHAULT J., Naumann-Godo M., NUSS E., Pierbattista M., PIRON F., Reposeur T., Strong A. W., Thayer J. B., VASILEIOU V., Bontemps S.

The origin of Galactic cosmic rays is a century-long puzzle. Indirect evidence points to their acceleration by supernova shockwaves, but we know little of their escape from the shock and their evolution through the turbulent medium surrounding massive stars. Gamma rays can probe their spreading through the ambient gas and radiation fields. The Fermi Large Area Telescope (LAT) has observed the star-forming region of Cygnus X. The 1- to 100-gigaelectronvolt images reveal a 50-parsec-wide cocoon of freshly accelerated cosmic rays that flood the cavities carved by the stellar winds and ionisation fronts from young stellar clusters. It provides an example to study the youth of cosmic rays in a superbubble environment before they merge into the older Galactic population.

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Strange cosmic ray hotspots stalk southern skies

Cosmic rays crashing into the Earth over the South Pole appear to be coming from particular locations, rather than being distributed uniformly across the sky. Similar cosmic ray "hotspots" have been seen in the northern skies too, yet we know of no source close enough to produce this pattern.
Between May 2009 and May 2010, IceCube detected 32 billion cosmic-ray muons, with a median energy of about 20 teraelectronvolts (TeV). These muons revealed, with extremely high statistical significance, a southern sky with some regions of excess cosmic rays ("hotspots") and others with a deficit of cosmic rays ("cold" spots).

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UHECRs
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Title: A correlation between the highest energy cosmic rays and nearby active galactic nuclei detected by Fermi
Authors: Rodrigo S. Nemmen, Charles Bonatto, Thaisa Storchi-Bergmann

We analyse the correlation of the positions of gamma-ray sources in the Fermi Large Area Telescope First Source Catalogue (1FGL) and the First LAT Active Galactic Nuclei (AGN) Catalogue (1LAC) with the arrival directions of ultra-high-energy cosmic rays (UHECRs) observed with the Pierre Auger Observatory, in order to investigate the origin of UHECRs. We find that Galactic sources and blazars identified in the 1FGL are not significantly correlated with UHECRs, while the 1LAC sources display a mild correlation (2.6 sigma level) on a ~2.4 degree angular scale. When selecting only the 1LAC AGNs closer than 200 Mpc, we find a strong association (5.4 sigma) between their positions and the directions of UHECRs on a ~17 degree angular scale; the probability of the observed configuration being due to an isotropic flux of cosmic rays is 5x10^{-8}. There is also a 5 sigma correlation with nearby 1LAC sources on a 6.5 degree scale. We identify 7 "gamma-ray loud" AGNs which are associated with UHECRs within ~17 degree and are likely candidates for the production sites of UHECRs: Centaurus A, NGC 4945, ESO 323-G77, 4C+04.77, NGC 1218, RX J0008.0+1450 and NGC 253. We interpret these results as providing additional support to the hypothesis of the origin of UHECRs in nearby extragalactic objects. As the angular scales of the correlations are large, we discuss the possibility that intervening magnetic fields might be considerably deflecting the trajectories of the particles on their way to Earth.

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