Search for Ultra-high-energy Photons from Gravitational Wave Sources with the Pierre Auger Observatory

A search for time-directional coincidences of ultra-high-energy (UHE) photons above 10 EeV with gravitational wave (GW) events from the LIGO/Virgo runs O1 to O3 is conducted with the Pierre Auger Observatory. Due to the distinctive properties of photon interactions and to the background expected from hadronic showers, a subset of the most interesting GW events is selected based on their localization quality and distance. Time periods of 1000 s around and 1 day after the GW events are analyzed. No coincidences are observed. Upper limits on the UHE photon fluence from a GW event are derived that are typically at & SIM;7 MeV cm(-2) (time period 1000 s) and & SIM;35 MeV cm(-2) (time period 1 day). Due to the proximity of the binary neutron star merger GW170817, the energy of the source transferred into UHE photons above 40 EeV is constrained to be less than 20% of its total GW energy. These are the first limits on UHE photons from GW sources

Arrival Directions of Cosmic Rays above 32 EeV from Phase One of the Pierre Auger Observatory

A promising energy range to look for angular correlations between cosmic rays of extragalactic origin and their sources is at the highest energies, above a few tens of EeV (1 EeV equivalent to 10^(18) eV). Despite the flux of these particles being extremely low, the area of similar to 3000 km^(2) covered at the Pierre Auger Observatory, and the 17 yr data-taking period of the Phase 1 of its operations, have enabled us to measure the arrival directions of more than 2600 ultra-high-energy cosmic rays above 32 EeV. We publish this data set, the largest available at such energies from an integrated exposure of 122,000 km^(2) sr yr, and search it for anisotropies over the 3.4 pi steradians covered with the Observatory. Evidence for a deviation in excess of isotropy at intermediate angular scales, with similar to 15 degrees Gaussian spread or similar to 25 degrees top-hat radius, is obtained at the 4 sigma significance level for cosmic-ray energies above similar to 40 EeV

Searches for Ultra-High-Energy Photons at the Pierre Auger Observatory

The Pierre Auger Observatory, which is the largest air-shower experiment in the world, offers unprecedented exposure to neutral particles at the highest energies. Since the start of data collection more than 18 years ago, various searches for ultra-high-energy (UHE, E greater than or similar to 10^(17) eV) photons have been performed, either for a diffuse flux of UHE photons, for point sources of UHE photons or for UHE photons associated with transient events such as gravitational wave events. In the present paper, we summarize these searches and review the current results obtained using the wealth of data collected by the Pierre Auger Observatory

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated 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 170817A) 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+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

SEARCH FOR 100 TEV GAMMA-RAY EMISSION FROM THE GALACTIC DISK

A search for UHE (greater-than-or-equal-to 100 TeV) diffuse gamma-ray emission from the Galactic disk has been carried out, through the excess in the cosmic-ray counting rate, by means of the EAS-TOP extensive air shower array at the Gran Sasso Laboratories. Measurements are performed from angular scales /b/ almost-equal-to 2-degrees (as in 100 MeV satellite experiments, and as expected from CR interactions with the ISM) to /b/ almost-equal-to 100. The obtained upper limits (90% c.l.) to the gamma-ray excess over the cosmic-ray flux from the Galactic disk region are I(gamma)/I(p) 130 TeV, corresponding to upper limits to the flux of I(gamma) < 3.2 x 10(-13) cm-2 s-1 rad-1, I(gamma) < 2.8 x 10(-13) cm-2 s- 1 rad-1, and I(gamma) < 4 x 10(-13) cm-2 S-1 rad-1.3971114815

UHE COSMIC-RAY EVENT RECONSTRUCTION BY THE ELECTROMAGNETIC DETECTOR OF EAS-TOP

UHE cosmic rays are studied by means of the detectors of the different components of secondaries produced by their interactions in the atmosphere (EAS). We describe and discuss the reconstruction techniques and accuracies of the e.m. detector of EAS-TOP. They allow, besides independent high resolution measurements of UHE gamma-ray astronomy, good correlation possibilities with the detectors of the different EAS components.3364167131032

A measurement of the solar and sidereal cosmic-ray anisotropy at E(0)similar to 10(14)eV

The results of the measurement of the cosmic-ray solar and sidereal anisotropies at primary energy E(0) approximate to 10(14) eV performed by the EAS-TOP Extensive Air Shower array (Campo Imperatore, National Gran Sasso Laboratories, 2005 m above sea level, latitude 42 degrees.5 N are presented. The measurement includes 4 years of data taking (1990, 1992, 1993, 1994) for a total of 1.3 x 10(9) events and is performed at two different mean primary energies: (E) over bar(0)(v) approximate to 1.5 x 10(14) eV and (E) over bar(0)(i) approximate to 2.5 x 10(14) eV. The two results are compatible (within 2 sigma) and can therefore be combined. The obtained amplitude and phase of the first harmonic in sidereal time are (in the equatorial plane) A(sid,delta=0c)((E) over bar(0) approximate to 2 x 10(14) eV) = (3.73 +/- 0.57) x 10(-4) and phi(sid) = 1.82 +/- 0.49 hr local sidereal time, with significance 6.5 sigma. The amplitude of the anisotropy exhibits the expected cos delta dependence. A first harmonic in solar time compatible with the expected Compton-Getting effect due to the motion of revolution of the Earth around the Sun is observed with significance 7.3 sigma. The corresponding measured amplitude and phase (also in the equatorial plane) are A(sol,delta=0o)=(4.06 +/- 0.55) x 10(-4) and phi(sol) = 4.92 +/- 0.53 hr, the expected values being 4.7 x 10(-4) and 6.0 hr. Different checks of stability of the detectors and consistency of the data are presented.4701150150

Search for gamma-ray bursts at photon energies E>=10 GeV and E>=80 TeV

The EAS-TOP extensive air shower array has been operating since 1992 in the search for gamma-ray bursts at primary energies E(1) greater than or equal to 10 GeV and E(2) greater than or equal to 80 TeV. The study is performed by searching for short transients in the cosmic-ray intensity in the single particle (E(1)) and extensive air shower (E(2)) counting rates at mountain altitude (2005 m above sea level). We discuss the method and the results obtained both in sky survey and in correlation with BATSE events. In both energy ranges, the observed fluctuations in the event rate obtained in the sky survey during similar to 800 days of live time are compatible with the statistical fluctuations of the cosmic-ray background. A single candidate of time duration Delta t similar to 2 s and energy fluence F(10 < E < 100 GeV) = 1.7 x 10(-4)/(cos theta)(10.5) ergs cm(-2) (where theta is the unknown zenith angle) has been observed on 1992 July 15 at 13:22:26 UT in the energy range E(1) greater than or equal to 10 GeV with significance 10.6 and 20.1 sigma in two measurement channels. In the analysis made in correlation with similar to 50 events detected by BATSE, no burst candidate was found in time coincidence or in the 2 hr interval, around the BATSE detection time. The following ranges of upper limits F-max to the energy fluence in the time interval Delta t(90) in which BATSE detected 90% of the counts are obtained: F-max = 2.3 x 10(-5)-7.4 x 10(-3) ergs cm(-2) (10 < E < 100 GeV) F-max = 1.6 x 10(-6)-3.3 x 10(-5) ergs cm(-2) (100 < E < 1000 TeV).4691130531