A new analysis of the dataset from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above 20 EeV with zenith angles up to 80 deg recorded before 2017 April 30. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0 sigma, the highest value of the test statistic being for energies above 39 EeV. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed.
COBISS.SI-ID: 5079291
The association of at least a dozen ultrahigh-energy cosmic-ray (UHECR) events with energy ?55 EeV detected by the Pierre Auger Observatory (PAO) from the direction of Centaurus-A, the nearest radio galaxy, supports the scenario of UHECR acceleration in the jets of radio galaxies. In this work, we model radio to very high energy (VHE,?100 \rm GeV) ?-ray emission from Cen A, including GeV hardness detected by Fermi-LAT and TeV emission detected by HESS.
COBISS.SI-ID: 5145595
Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature. Clues to their origin come from studying the distribution of their arrival directions. Using 3e4 cosmic rays above 8e18 electron volts, recorded with the Pierre Auger Observatory from a total exposure of 76,800 square kilometers steradian year, we report an anisotropy in the arrival directions. The anisotropy, detected at more than the 5.2? level of significance, can be described by a dipole with an amplitude of 6.5+1.3-0.9% towards right ascension ?d=100±10 degrees and declination ?d=-24+12-13 degrees. That direction indicates an extragalactic origin for these ultra-high energy particles.
COBISS.SI-ID: 4921595
On 2017 August 17 a binary neutron star coalescence candidate GW170817 with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst GRB with a time delay of 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+-8 Mpc and with component masses consistent with neutron stars. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches.
COBISS.SI-ID: 4941051
Simultaneous measurements of air showers with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for EeV photon point sources. Several Galactic and extragalactic candidate objects are grouped in classes to reduce the statistical penalty of many trials from that of a blind search and are analyzed for a significant excess above the background expectation. The presented search does not find any evidence for photon emission at candidate sources, and combined p-values for every class are reported. Particle and energy flux upper limits are given for selected candidate sources. These limits significantly constrain predictions of EeV proton emission models from non-transient Galactic and nearby extragalactic sources, as illustrated for the particular case of the Galactic center region.
COBISS.SI-ID: 4727035