H. Salazar

The Surface Detector System of the Pierre Auger Observatory

The Pierre Auger Observatory is designed to study cosmic rays with energies greater than 10 19 eV. Two sites are envisaged for the observatory, one in each hemisphere,

OBSERVATION OF SMALL-SCALE ANISOTROPY IN THE ARRIVAL DIRECTION DISTRIBUTION OF TeV COSMIC RAYS WITH HAWC

The High-Altitude Water Cherenkov (HAWC) Observatory is sensitive to gamma rays and charged cosmic rays at TeV energies. The detector is still under construction, but data acquisition with the partially deployed detector started in 2013. An analysis of the cosmic-ray arrival direction distribution based on 4.9 × 1010 events recorded between 2013 June and 2014 February shows anisotropy at the 10–4 level on angular scales of about 10°. The HAWC cosmic-ray sky map exhibits three regions of significantly enhanced cosmic-ray flux; two of these regions were first reported by the Milagro experiment. A third region coincides with an excess recently reported by the ARGO-YBJ experiment. An angular power spectrum analysis of the sky shows that all terms up to l = 15 contribute significantly to the excesses.

Search for Gamma-Rays from the Unusually Bright GRB 130427A with the HAWC Gamma-Ray Observatory

The first limits on the prompt emission from the long gamma-ray burst (GRB) 130427A in the >100 GeV energy band are reported. GRB 130427A was the most powerful burst ever detected with a redshift z 0.5 and featured the longest lasting emission above 100 MeV. The energy spectrum extends at least up to 95 GeV, clearly in the range observable by the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, a new extensive air shower detector currently under construction in central Mexico. The burst occurred under unfavorable observation conditions, low in the sky and when HAWC was running 10% of the final detector. Based on the observed light curve at MeV-GeV energies, eight different time periods have been searched for prompt and delayed emission from this GRB. In all cases, no statistically significant excess of counts has been found and upper limits have been placed. It is shown that a similar GRB close to zenith would be easily detected by the full HAWC detector, which will be completed soon. The detection rate of the full HAWC detector may be as high as one to two GRBs per year. A detection could provide important information regarding the high energy processes at work and the observation of a possible cut-off beyond the Fermi Large Area Telescope energy range could be the signature of gamma-ray absorption, either in the GRB or along the line of sight due to the extragalactic background light.

Search for TeV Gamma-Ray Emission from Point-like Sources in the Inner Galactic Plane with a Partial Configuration of the HAWC Observatory

Author(s): Abeysekara, AU; Alfaro, R; Alvarez, C; Alvarez, JD; Arceo, R; Arteaga-Vela Zquez, JC; Solares, HAA; Barber, AS; Baughman, BM; Bautista-Elivar, N; Reyes, ADB; Belmont, E; Benzvi, SY; Bernal, A; Braun, J; Caballero-Mora, KS; Capistran, T; Carraminana, A; Casanova, S; Castillo, M; Cotti, U; Cotzomi, J; Leon, SCD; Fuente, EDL; Leon, CD; Deyoung, T; Diaz Hernandez, R; Dingus, BL; Duvernois, MA; Ellsworth, RW; Enriquez-Rivera, O; Fiorino, DW; Fraija, N; Garfias, F; Gonzalez, MM; Goodman, JA; Gussert, M; Hampel-Arias, Z; Harding, JP; Hernandez, S; Huntemeyer, P; Hui, CM; Imran, A; Iriarte, A; Karn, P; Kieda, D; Lara, A; Lauer, RJ; Lee, WH; Lennarz, D; Vargas, HL; Linnemann, JT; Longo, M; Raya, GL; Malone, K; Marinelli, A; Marinelli, SS; Martinez, H; Martinez, O; Martinez-Castro, J; Matthews, JA; Miranda-Romagnoli, P; Moreno, E; Mostafa, M; Nellen, L; Newbold, M; Noriega-Papaqui, R; Patricelli, B; Pelayo, R; Perez-Perez, EG; Pretz, J; Ren, Z; Riviere, C; Rosa-Gonzalez, D; Salazar, H; Greus, FS; Sandoval, A; Schneider, M; Sinnis, G; Smith, AJ; Woodle, KS; Springer, RW; Taboada, I; Tibolla, O; Tollefson, K | Abstract:

Ultraviolet flashes in the equatorial region of the Earth

Intense ultraviolet flashes with a duration of 1 to 64 ms have been detected by the UV detector (wavelengths 300–400 nm) that operates at the Universitetsky-Tatiana MSU satellite. Most flashes occur in the equatorial region of the Earth. The nature of the observed flashes is discussed.

Atmospheric ultraviolet and red-infrared flashes from Universitetsky-Tatiana-2 satellite data

Millisecond ultraviolet (240–400 nm) and red-infrared (610–800 nm) flashes were detected in the nighttime atmosphere with the scientific payload installed onboard the Universitetsky-Tatiana-2 micro-satellite. Flashes with various numbers of photons, from 1020 to 1026, were detected within the atmospheric area 300 km in diameter observed by the detector. The flashes differ in duration and temporal profile: from single short flashes ∼1 ms in duration to flashes with a complex profile more than 100 ms in duration. Different global geographic distributions are observed for flashes with different numbers of photons. Flashes with fewer than 1022 photons are distributed uniformly over the Earth’s map. Flashes with more than 1022 photons are concentrated near the equator and above the continents. Series of flashes were observed in one turn of the satellite when flying not only over thunderstorm regions but also over cloudless ones. The flash number distribution has been derived from the ratio of the numbers of red-infrared and ultraviolet photons. As applied to discharges in the upper atmosphere, whose glow is dominated by the emission in the first and second positive systems of molecular nitrogen bands (1PN2 and 2PN2), this distribution is equivalent to the flash altitude distribution in the atmosphere. The observed ratio of the numbers of photons in red-infrared and ultraviolet flashes agrees with the calculated one for electric discharges at altitudes higher than 50 km. In-orbit measurements of the charged particle flux (with a threshold energy for electrons of 1 MeV) provide no evidence for a synchronous occurrence of an ultraviolet flash and a burst in the particle flux in the orbit.

KLYPVE/TUS space experiments for study of ultrahigh-energy cosmic rays

The KLYPVE space experiment has been proposed to study the energy spectrum, composition, and arrival direction of ultrahigh-energy cosmic rays (UHECR) by detecting from satellites the atmosphere fluorescence and scattered Cherenkov light produced by EAS, initiated by UHECR particles. The TUS setup is a prototype KLYPVE instrument. The aim of the TUS experiment is to detect dozens of UHECR events in the energy region of the GZK cutoff, to measure the light background, to test the atmosphere control methods, and to study stability of the optical materials, PMTs, and other instrumental parts in space environment.

UV Radiation from the Night-Time Atmosphere seen from the “Universitetsky-Tatiana” Satellite

Detectors on the “Universitetsky‐Tatiana” satellite measured a smoothly varying intensity of UV radiation from the night‐time atmosphere in the nadir direction and the intensity of the energetic electron flux at the orbit. At high latitudes the UV intensity in the auroral oval is interpreted as being due to electrons penetrating into the atmosphere. At middle latitudes the UV intensity is an order of magnitude less and more data are needed to reveal the origin of this radiation. Millisecond flashes of UV radiation were observed. The flashes’ energy, temporal profile and global distribution are similar to these parameters for Transient Luminous Events (TLEs). These studies will be continued aboard the next satellite “Tatiana‐2”.

Calibration and monitoring of water Cherenkov detectors with stopping and crossing muons

Abstract The Auger Observatory water Cherenkov detectors (WCD) will require that the initial calibration and subsequent monitoring of each of the WCDs be done in a remote way. We present a method to perform these tasks based on the detection of muons decaying inside the detectors and the application of adequate selection cuts. This technique may be complemented with another based on muons crossing the WCDs. Samples of decaying and crossing muon events were obtained with a WCD prototype to demonstrate the viability of the techniques. Three clear peaks of PMT charge distributions were identified. All of them are useful for calibration and monitoring of WCDs: one for stopping muons, one for decay electrons and one for crossing muons. The mean value of the peak found in the decay-electron charge distribution is 0.18 times the corresponding value for vertically crossing muons; likewise, the mean value of the peak in the charge distribution of crossing muons (excluding corner clipping muons) is 6.1 times the value for decay electrons in a tank of our dimensions; finally, the mean value of the peak in the charge distribution of stopping muons is 0.55 times the value for decay electrons. The techniques described can be applied equally well to unsegmented or segmented Auger tanks as each of the three PMTs of an Auger WCD can be self-triggered independently. The experimental data are well reproduced by numerical simulations.

Energetic Particles Impacting the Upper Atmosphere in Connection with Transient Luminous Event Phenomena: Russian Space Experiment Programs

In Russia several space missions are now planned to study transient luminous events in the atmosphere and high energy charged particles at satellite altitudes. The experimental goal is to investigate the origin of the high energy electrons and gamma‐ray quanta for specific transient luminous events (TLEs) and their role in the ionosphere‐magnetosphere system. Simultaneous measurements of electrons at the orbit of the satellite and TLE atmospheric radiation in many wavelength bands will be performed in two missions, Tatiana‐2 and RELEC. In the TUS mission UV transient event detection will be accompanied by measurements of the weak UV emission from the “seed” electrons of extensive air showers of extremely high primary energies.