Search for large-scale coincidences in network observation of cosmic ray air showers

Abstract

The Large Area Air Shower (LAAS) group has been performing a network observation of extensive air showers (EAS) since 1996 in Japan. Eight compact EAS arrays (ten in the near future) are operating simultaneously and independently at distant stations (up to ≈ 1000 km), constituting a gigantic detector system as a whole. Using five stations' datasets, large-scale coincidences of EAS have been searched for with the aim of detecting signals from extremely short bursts in the universe. By comparing arrival times and arrival directions of all registered EAS, three coincident and parallel EAS pairs were extracted out of a sea of background cosmic rays. One of them was observed almost from the direction of the Crab Nebula, a previously reported ultra-high-energy γ-ray source. The first application reported here allows the analysis techniques to be tested and demonstrates the potential of observations with the full operation of the network detector system.

Search for correlated high energy cosmic ray events with CHICOS

“…We know of no previous cosmic ray experiment that would be sensitive to correlated shower events at these energies separated by 10-50 km. The LAAS experiment [9] has only eight sites at much larger distances (∼500 km) and would have seen <1 event given the rate we observe (assuming the correlations persist to those larger distance scales).…”

CZELTA: An overview of the CZECH large-area time coincidence array

“…It covers local detection networks in Canada and the USA (ALTA, SALTA (SAL), WALTA (WAL), CHICOS (CHI), CROP (CRO), etc.). A similar project is running in Japan (LAAS (Ochi et al, 2003)) and detection stations are being built on the roofs of European high schools, too -in Sweden (SEASA (SEA)), Germany (SkyView (Sky)), the Netherlands (HiSPARC (HiS)), Great Britain (Cosmic School (Cos)) among other countries.…”

“…In 1994 Swiss group (Carrel and Martin, 1994) reported an interesting temporal increase of distant time-correlated showers. LAAS group (Ochi et al, 2003) reported few interesting candidates of correlated showers on large distance. However, interpretation that these events were only accidentally correlated, is also plausible.…”

The primary energy spectrum with the Linsley method correcting heavy primary effects in the LAAS experiments

“…The Large Area Air Shower (LAAS) experiments [1,2] have been observing cosmic rays with compact Extensive Air Shower (EAS) arrays, and have maintained EAS arrays at several institutes since 1996. The purposes of LAAS experiments are to study the primary energy spectrum, anisotropy of high energy cosmic rays, and simultaneous and parallel EAS events [3][4][5][6][7].…”