Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera-electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray-emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent a series of upgrades, involving the exchange of the MAGIC-I camera and its trigger system, as well as the upgrade of the readout system of both telescopes. We use observations of the Crab Nebula taken at low and medium zenith angles to assess the key performance parameters of the MAGIC stereo system. For low zenith angle observations, the standard trigger threshold of the MAGIC telescopes is ∼ 50 GeV. The integral sensitivity for point-like sources with Crab Nebula-like spectrum above 220 GeV is (0.66 ± 0.03)% of Crab Nebula flux in 50 h of observations. The angular resolution, defined as the σ of a 2-dimensional Gaussian distribution, at those energies is ≲ 0.07°, while the energy resolution is 16%. We also re-evaluate the effect of the systematic uncertainty on the data taken with the MAGIC telescopes after the upgrade. We estimate that the systematic uncertainties can be divided in the following components: < 15% in energy scale, 11%-18% in flux normalization and ± 0.15 for the energy spectrum power-law slope

he Pierre Auger Observatory, located on a vast, high plain in western\ud Argentina, is the world's largest cosmic ray observatory. The objectives\ud of the Observatory are to probe the origin and characteristics of cosmic\ud rays above 10(17) eV and to study the interactions of these, the most\ud energetic particles observed in nature. The Auger design features an\ud array of 1660 water Cherenkov particle detector stations spread over\ud 3000 km(2) overlooked by 24 air fluorescence telescopes. In addition,\ud three high elevation fluorescence telescopes overlook a 23.5 km(2),\ud 61-detector infilled array with 750 in spacing. The Observatory has been\ud in successful operation since completion in 2008 and has recorded data\ud from an exposure exceeding 40,000 km(2) sr yr. This paper describes the\ud design and performance of the detectors, related subsystems and\ud infrastructure that make up the Observatory

We report on the γ -ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) γ -ray spectrum above 0.3 GeV can be well described by a power-law function with photon index Γ = 1.78 ± 0.02 and average photon flux F (>0.3 GeV) = (7.23 ± 0.16) × 10 −8 ph cm −2 s −1 . Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor ∼3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in γ -rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.

Editor: S. DodelsonWe report a measurement of the flux of cosmic rays with unprecedented precision and statistics using the Pierre Auger Observatory. Based on fluorescence observations in coincidence with at least one surface detector we derive a spectrum for energies above 10 18 eV. We also update the previously published energy spectrum obtained with the surface detector array. The two spectra are combined addressing the systematic uncertainties and, in particular, the influence of the energy resolution on the spectral shape. 242Pierre Auger Collaboration / Physics Letters B 685 (2010) The spectrum can be described by a broken power law E −γ with index γ = 3.3 below the ankle which is measured at log 10 (E ankle /eV) = 18.6. Above the ankle the spectrum is described by a power law with index 2.6 followed by a flux suppression, above about log 10 (E/eV) = 19.5, detected with high statistical significance.