Chicago Air Shower Array

Chicago Air Shower Array
Location(s)	Utah
Coordinates	40°12′N112°48′W / 40.2°N 112.8°W
Organization	University of Chicago
Altitude	1450 m
Wavelength	Ultra high energy (E> 100 TeV)
Built	1988–1991
Collecting area	235,000 square-meters
	Location of Chicago Air Shower Array
	[ edit on Wikidata]

Last updated April 05, 2024

The Chicago Air Shower Array (CASA) was a significant ultra high high-energy astrophysics experiment operating in the 1990s. It consisted of a very large array of scintillation detectors located at Dugway Proving Grounds in Utah, USA, approximately 80 kilometers southwest of Salt Lake City. The full CASA detector, consisting of 1089 detectors began operating in 1992 in conjunction with a second instrument, the Michigan Muon Array (MIA), under the name CASA-MIA. MIA was made of 2500 square meters of buried muon detectors. At the time of its operation, CASA-MIA was the most sensitive experiment built to date in the study of gamma ray and cosmic ray interactions at energies above 100 TeV (10¹⁴ electronvolts). Research topics on data from this experiment covered a wide variety of physics issues, including the search for gamma rays from Galactic sources (especially the Crab Nebula and the X-ray binaries Cygnus X-3 and Hercules X-1) and extragalactic sources (active Galactic nuclei and gamma-ray bursts), the study of diffuse gamma-ray emission (an isotropic component or from the Galactic plane), and measurements of the cosmic ray composition in the region from 100 to 100,000 TeV. For the topic of composition, CASA-MIA worked in conjunction with several other experiments at the same site: the Broad Laterial Non-imaging Cherenkov Array (BLANCA), the Dual Imaging Cherenkov Experiment (DICE) and the Fly's Eye HiRes prototype experiment. CASA-MIA operated continuously between 1992 and 1999. In summer 1999, it was decommissioned.

Specifications and design

Plan view of the CASA-MIA detectors at Dugway Proving Grounds in Utah, USA. CASA consisted of 1089 scintillation detectors on a square 15 m x 15 m grid. MIA consisted of 1024 scintillation counters arranged in 16 patches. Five small Cherenkov telescopes were co-located at the site and used for angular alignment. CASA-MIA.png — Plan view of the CASA-MIA detectors at Dugway Proving Grounds in Utah, USA. CASA consisted of 1089 scintillation detectors on a square 15 m x 15 m grid. MIA consisted of 1024 scintillation counters arranged in 16 patches. Five small Cherenkov telescopes were co-located at the site and used for angular alignment.

CASA was built to study the possibility of astrophysical sources of ultra high energy (UHE, E > 100 TeV) gamma-ray emission (see Science below). Gamma rays at these energies interact in the Earth's atmosphere to create an extensive air shower that propagates to the Earth's surface. At the surface, the shower consists predominantly of electrons/positrons, low-energy gamma rays, muons, and some hadrons, with a typical footprint on the ground of 50–100 m. (There is also a component of Cherenkov radiation reaching the ground that can be recorded by imaging atmospheric Cherenkov telescopes). An air shower array is a distributed set of particle detectors (scintillation detector, water Cherenkov detectors, etc.) spread out on the ground to record the passage of the shower particles. The primary particle direction is estimated from the relative arrival time of the shower hitting each detector; the primary particle energy is estimated from the number of particles recorded in each detector and from the lateral distribution of those measurements.

Aerial view of the Chicago Air Shower Array (CASA) and associated detectors at Dugway Proving Grounds, Utah, USA. The CASA scintillation detectors are the white square boxes laid out on a 15-meter grid spacing. At the center of the array (left of center in this image) is the Fly's Eye II detector. Casa-aerial-2.jpg — Aerial view of the Chicago Air Shower Array (CASA) and associated detectors at Dugway Proving Grounds, Utah, USA. The CASA scintillation detectors are the white square boxes laid out on a 15-meter grid spacing. At the center of the array (left of center in this image) is the Fly's Eye II detector.

Prior to CASA, air shower arrays were typically modest in size, typically consisting of 50-100 detectors covering an area of around 50,000 square meters. The plan for CASA was to build a much more sensitive experiment that would be much larger in size, use state-of-the-art electronics, and be coupled with a large array of muon detectors (MIA).^[1] The expectation was that showers initiated by gamma rays would contain far fewer muons compared to showers initiated by cosmic rays.^[2] The original plan was for an array of 1064 detectors,^[3] but the number was subsequently increased to 1089.^[4]

Some of the key design features CASA-MIA were the following:^[5]

1089 scintillation detectors, spread out on a square grid of 33 x 33 detectors, with a detector spacing of 15 m, covering a total area of 230,000 square meters.
A CASA detector consisted of four separate scintillation counters; each counter consisted of a piece of acrylic scintillator 61 cm x 61 cm x 1.27 cm in size and read out by a single photomultiplier tube (PMT, either Amperex 2212 or EMI 9256).
Each CASA detector contained a local high voltage module and a custom-made electronics board that allowed each detector to take data independently of other detectors.
The CASA detectors were connected to a central controller via a rib-spine network consisting of coaxial cables with three functions: trigger request, trigger acknowledge and Ethernet.
The muon array (MIA) consisted of 1024 scintillation counters, each of size 1.9 m x 1.3 m. The muon counters were arranged in 16 patches of 64 counters each and were buried beneath 3 m below the surface. Signals from the MIA counters were run under the ground to a central trailer where relative arrival times were measured by conventional LeCroy 4290 time-to-digital converters (TDCs).

The trigger and data-acquisition sequence for CASA was complex because of the distributed electronics; it worked as follows:^[5]

The PMT signals in each counter are each sampled by a low-level and high-level discriminator. The low discriminator level is set to around 0.1 of the signal from a typical minimum-ionizing particle; the high discriminator level is set to around three times that of the low level.
A detector with two or more counters firing the high-level discriminator in 30 nsec is "alerted"; a detector with three or more counters firing the high-level discriminator if 30 nsec is "triggered.
Alerted stations carry out local data acquisition tasks and inhibit further triggering of the station. Time-to-voltage converters on the local electronics board hold the four relative times of the four counters in a detector (determined by the crossing time of the low-level discriminator) and four times corresponding to the times of arrival of pulses sent by the neighboring four detectors, if they have been alerted. Sample and hold circuits record the four charges corresponding to the integrals of the PMT signals from each counter. Alerted stations wait for 10 μsecs for a trigger acknowledge signal from the central station; if no signal is received, their data are discarded.
Triggered stations place a fast current pulse (5 mA, 10 μsec duration) onto the rib trigger request coaxial cable (RG-58, 50Ω); these signals are propagated to a central trigger box via a repeater at the rib/spine junction and a spine trigger request coaxial cable (RG-8, 50Ω).
The entire array is triggered when three trigger request levels are received by the central trigger box. Then, a fast signal (12V, μsec duration) is placed on the trigger acknowledge coaxial line where it is propagated back to each station via the rib-spine network. Upon receipt of a trigger acknowledge signal, alerted stations digitize their eight times and four charges through a multiplexer and a 10-bit analog-to-digital converter (ADC). The digitized data are stored in a memory buffer under the control of a microprocessor (Intel 80186). The dominant deadtime for the array is when data are digitized (approximately 0.5 msec).
Periodically (typically every 30 sec), the station electronic boards receive a command over Ethernet to transmit their data to a central computer (DEC μVAX III+). Each board switches their memory buffer and continues to accumulate data; the previous recorded data are transmitted over the rib-spine network to the center where they are recorded on disk.

CASA, and its associated muon array MIA, achieved excellent performance and was the state-of-the-art in air shower experiments in the ultra high energy band for a considerable period of time after its operational period in the 1990s. Only in the late 2010s have experiments such as the Tibet Air Shower Array and the High Altitude Water Cherenkov Experiment surpassed CASA-MIA in sensitivity at energies above 100 TeV. The median gamma-ray energy for a source passing near zenith was 115 TeV. The gamma-ray angular resolution varied with the size (number of particles) in the detected shower and was approximately 0.7 degrees for showers with the median number of particles, improving to 0.25 degrees at higher energies.^[5] The muon array provided important capability to reject background cosmic ray events; at the median energy of 115 TeV, the fraction of cosmic ray events passing the muon selection criteria for gamma rays was 0.06 (i.e. approximately 17 cosmic ray events were rejected for each one accepted). At higher energies, the background rejection power was significantly increased; for example, at a median energy of 5,000 TeV, the fraction of cosmic rays passing muon selection criteria was reduced to approximately 0.0001.

History

The scientific motivation for CASA came from intriguing results from several experiments in the 1980s. These experiments reported excess air shower events from the direction of two well-known Galactic X-ray binary sources: Cygnus X-3 and Hercules X-1. In 1983, the Kiel and Haverah Park experiments reported an excess of events from the direction of Cygnus X-3, where the arrival times of the events appeared to be modulated by the 4.8-hour orbital periodicity of the binary source.^[6]^[7] The statistical significance of each signal was weak (around four standard deviations above background), but the results implied that Cygnus X-3 was a luminous emitter of ultra high energy gamma rays and that, in order to do so, it must be a very efficient accelerator of high energy cosmic rays and hence it could provide a large fraction of the pervading flux of cosmic ray particles in our Galaxy.

After these results, a number of groups around the world began designing, or improving, air shower arrays to make follow-up studies. One of these groups was from the University of Chicago,led by James Cronin. Cronin's idea was to build a definitive experiment that could easily verify, or refute, the results on Cygnus X-3.^[1] The experiment would be much larger (and much more sensitive) than the Kiel or Haverah Park experiments and it would use a large array of muon detectors to reject the background of hadronic cosmic ray events (i.e. protons and nuclei). (Showers initiated by gamma-ray primaries are expected to have far fewer muons than those initiated by cosmic ray primaries). Cronin assembled a team of scientists (discussed in Collaboration) to develop and construct CASA. The University of Chicago group was partnered with groups from the University of Michigan and the University of Utah, who had already constructed a muon array and smaller air shower array, and the site for CASA would be on Dugway Proving Grounds.

The construction and deployment of CASA took place between 1988 and 1991. Construction activities were carried out at the University of Chicago in the Accelerator Building of the Enrico Fermi Institute. The completed scintillation detectors, along with electronics, were shipped to Utah in large semi-trailers, where they were installed by students, postdocs and faculty. An initial array of 49 detectors became operational in 1989, followed by a 529-detector array in 1990. Standard science operation of the full 1089-detector CASA array (along with the 1024-counter muon array) started in December 1991. CASA operated very successfully, largely without interruption, until 1997. During that time a total of approximately 3 billion air showers events were recorded. Partial operations continued for several more years, in conjunction with the BLANCA and DICE experiments. The various experiments at the site, including CASA, ceased operation in 1999.

Science

The scientific results from CASA-MIA encompassed a dozen scientific publications and covered topics in three broad areas of high-energy astrophysics: gamma-ray point sources, diffuse gamma-ray sources, and cosmic ray physics.

Gamma-ray point sources: CASA-MIA set stringent limits on the emission from all sources that had been reported by earlier experiments, including Cygnus X-3 and Hercules X-1,^[8] the Crab Nebula,^[9] and known high-energy active galactic nuclei.^[10] For these sources, the CASA-MIA limits were typically two to three orders of magnitude lower than the flux levels reported by the previous instruments. Searches were also made for transient and period emission from point sources and a general survey of the overhead sky was also carried out.^[11]
Diffuse gamma-ray sources: the rejection power of the large muon array allowed CASA-MIA to study diffuse gamma-ray sources with great sensitivity. The most significant result came from a search of diffuse isotropic emission, which provided a limit on the electromagnetic fraction of the cosmic rays at a level less than 2 x 10⁻⁵ at the highest energies.^[12] Another significant result came from a study of diffuse emission from the Galactic plane.^[13] A separate study searched for bursts from arbitrary directions in the sky to constrain short timescale cosmic events, such as the explosions of primordial black holes.
Cosmic ray physics: with its large and uniform air shower array, couple with a large muon detector, CASA-MIA had good capability to making measurements of the properties of the ultra high energy cosmic rays. The electron and muon shower size distributions (determined from CASA and MIA, respectively) were used to measure the cosmic ray energy spectrum between 100 and 10,000 TeV.^[14] The CASA-MIA results showed a smooth steepening of the spectrum, in contrast with some earlier experiments that reported a sharper feature (known as the "knee"). CASA-MIA measurements of the cosmic ray composition were made from a combined fit to the surface and muon detector data and indicated a mixed composition at lower energies (below 1,000 TeV) that evolved smoothly to a heavier composition at energies approaching 10,000 TeV.^[15] A separate, and complementary, measurement of the cosmic ray composition was made by the BLANCA instrument that operated in conjunction with CASA-MIA and used the lateral distribution of the Cherenkov radiation in air showers.^[16]

Scientific collaborations

The CASA project was conceived by James W. Cronin and the design and construction were carried out by a team of scientists, engineers and technicians in the Enrico Fermi Institute of the University of Chicago (see ^[1] for more details). The initial core group of scientists consisted of Cronin, postdoctoral fellows Kenneth Gibbs, Brian Newport, Rene Ong, and Leslie Rosenberg, and graduate students Nicholas Mascarenhas, Hans Krimm and Timothy McKay. During the operational phase of CASA, the Chicago group included postdoctoral fellows Mark Chantell, Corbin Covault, Brian Fick and Lucy Fortson, Kevin Green, and graduate students Alexandre Borione, Joseph Fowler and Scott Oser. The Michigan Muon Array was constructed by a team of researchers from the University of Michigan, including James Matthews, David Nitz, Daniel Sinclair, and John van der Velde, post-doc Kevin Green, and graduate students Mike Catanese and Ande Kennedy Glasmacher.

Related Research Articles

Cosmic rays or astroparticles are high-energy particles or clusters of particles that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own galaxy, and from distant galaxies. Upon impact with Earth's atmosphere, cosmic rays produce showers of secondary particles, some of which reach the surface, although the bulk are deflected off into space by the magnetosphere or the heliosphere.

MAGIC is a system of two Imaging Atmospheric Cherenkov telescopes situated at the Roque de los Muchachos Observatory on La Palma, one of the Canary Islands, at about 2200 m above sea level. MAGIC detects particle showers released by gamma rays, using the Cherenkov radiation, i.e., faint light radiated by the charged particles in the showers. With a diameter of 17 meters for the reflecting surface, it was the largest in the world before the construction of H.E.S.S. II.

HEGRA, which stands for High-Energy-Gamma-Ray Astronomy, was an atmospheric Cherenkov telescope for Gamma-ray astronomy. With its various types of detectors, HEGRA took data between 1987 and 2002, at which point it was dismantled in order to build its successor, MAGIC, at the same site.

<span class="mw-page-title-main">Air shower (physics)</span> Cascade of atmospheric subatomic particles

Air showers are extensive cascades of subatomic particles and ionized nuclei, produced in the atmosphere when a primary cosmic ray enters the atmosphere. When a particle of the cosmic radiation, which could be a proton, a nucleus, an electron, a photon, or (rarely) a positron, interacts with the nucleus of a molecule in the atmosphere, it produces a vast number of secondary particles, which make up the shower. In the first interactions of the cascade especially hadrons are produced and decay rapidly in the air, producing other particles and electromagnetic radiation, which are part of the shower components. Depending on the energy of the cosmic ray, the detectable size of the shower can reach several kilometers in diameter.

The High Resolution Fly's Eye or HiRes detector was an ultra-high-energy cosmic ray observatory that operated in the West Desert of Utah from May 1997 until April 2006. HiRes used the "atmospheric fluorescence" technique that was pioneered by the Utah group first in tests at the Volcano Ranch experiment and then with the original Fly's Eye experiment. The experiment first ran as the HiRes prototype in a tower configuration operating in conjunction with the CASA and MIA. The prototype was later reconfigured to view 360 degrees in azimuth. HiRes-II followed later and was located on a hilltop about 13km away. HiRes-I and HiRes-II operated in stereo.

The Pierre Auger Observatory is an international cosmic ray observatory in Argentina designed to detect ultra-high-energy cosmic rays: sub-atomic particles traveling nearly at the speed of light and each with energies beyond 10¹⁸ eV. In Earth's atmosphere such particles interact with air nuclei and produce various other particles. These effect particles (called an "air shower") can be detected and measured. But since these high energy particles have an estimated arrival rate of just 1 per km² per century, the Auger Observatory has created a detection area of 3,000 km² (1,200 sq mi)—the size of Rhode Island, or Luxembourg—in order to record a large number of these events. It is located in the western Mendoza Province, Argentina, near the Andes.

The IceCube Neutrino Observatory is a neutrino observatory constructed at the Amundsen–Scott South Pole Station in Antarctica. The project is a recognized CERN experiment (RE10). Its thousands of sensors are located under the Antarctic ice, distributed over a cubic kilometre.

In particle physics, a shower is a cascade of secondary particles produced as the result of a high-energy particle interacting with dense matter. The incoming particle interacts, producing multiple new particles with lesser energy; each of these then interacts, in the same way, a process that continues until many thousands, millions, or even billions of low-energy particles are produced. These are then stopped in the matter and absorbed.

IACT stands for imaging atmosphericCherenkov telescope or technique. It is a device or method to detect very-high-energy gamma ray photons in the photon energy range of 50 GeV to 50 TeV.

<span class="mw-page-title-main">Neutrino detector</span> Physics apparatus which is designed to study neutrinos

A neutrino detector is a physics apparatus which is designed to study neutrinos. Because neutrinos only weakly interact with other particles of matter, neutrino detectors must be very large to detect a significant number of neutrinos. Neutrino detectors are often built underground, to isolate the detector from cosmic rays and other background radiation. The field of neutrino astronomy is still very much in its infancy – the only confirmed extraterrestrial sources as of 2018 are the Sun and the supernova 1987A in the nearby Large Magellanic Cloud. Another likely source is the blazar TXS 0506+056 about 3.7 billion light years away. Neutrino observatories will "give astronomers fresh eyes with which to study the universe".

VERITAS is a major ground-based gamma-ray observatory with an array of four 12 meter optical reflectors for gamma-ray astronomy in the GeV – TeV photon energy range. VERITAS uses the Imaging Atmospheric Cherenkov Telescope technique to observe gamma rays that cause particle showers in Earth's atmosphere that are known as extensive air showers. The VERITAS array is located at the Fred Lawrence Whipple Observatory, in southern Arizona, United States. The VERITAS reflector design is similar to the earlier Whipple 10-meter gamma-ray telescope, located at the same site, but is larger in size and has a longer focal length for better control of optical aberrations. VERITAS consists of an array of imaging telescopes deployed to view atmospheric Cherenkov showers from multiple locations to give the highest sensitivity in the 100 GeV – 10 TeV band. This very high energy observatory, completed in 2007, effectively complements the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope due to its larger collection area as well as coverage in a higher energy band.

The GRAPES-3 experiment located at Ooty in India started as a collaboration of the Indian Tata Institute of Fundamental Research and the Japanese Osaka City University, and now also includes the Japanese Nagoya Women's University.

Milagro was a ground-based water Cherenkov radiation telescope situated in the Jemez Mountains near Los Alamos, New Mexico at the Fenton Hill Observatory site. It was primarily designed to detect gamma rays but also detected large numbers of cosmic rays. It operated in the TeV region of the spectrum at an altitude of 2530 m. Like conventional telescopes, Milagro was sensitive to light but the similarities ended there. Whereas "normal" astronomical telescopes view the universe in visible light, Milagro saw the universe at very high energies. The light that Milagro saw was about 1 trillion times more energetic than visible light. While these particles of light, known as photons, are the same as the photons that make up visible light, they behave quite differently due to their high energies.

A cosmic-ray observatory is a scientific installation built to detect high-energy-particles coming from space called cosmic rays. This typically includes photons, electrons, protons, and some heavier nuclei, as well as antimatter particles. About 90% of cosmic rays are protons, 9% are alpha particles, and the remaining ~1% are other particles.

The GAMMA experiment is a study of:

<span class="mw-page-title-main">NEVOD</span>

NEVOD is a neutrino detector and cosmic ray experiment that attempts to detect Cherenkov radiation arising from interactions between water and charged particles. It represents the first attempt to perform such measurements at the Earth's surface; it is because of this surface deployment that the experiment is also able to investigate cosmic rays. NEVOD is situated at the Moscow Engineering Physics Institute (MEPhI).

The Tunka experiment now named TAIGA measures air showers, which are initiated by charged cosmic rays or high energy gamma rays. TAIGA is situated in Siberia in the Tunka valley close to lake Baikal. Meanwhile, TAIGA consists of five different detector systems: Tunka-133, Tunka-Rex, and Tunka-Grande for charged cosmic rays; Tunka-HiSCORE and Tunka-IACT for gamma astronomy. From the measurements of each detector it is possible to reconstruct the arrival direction, energy and type of the cosmic rays, where the accuracy is enhanced by the combination of different detector systems.

Very-high-energy gamma ray (VHEGR) denotes gamma radiation with photon energies of 100 GeV (gigaelectronvolt) to 100 TeV (teraelectronvolt), i.e., 10¹¹ to 10¹⁴ electronvolts. This is approximately equal to wavelengths between 10⁻¹⁷ and 10⁻²⁰ meters, or frequencies of 2 × 10²⁵ to 2 × 10²⁸ Hz. Such energy levels have been detected from emissions from astronomical sources such as some binary star systems containing a compact object. For example, radiation emitted from Cygnus X-3 has been measured at ranges from GeV to exaelectronvolt-levels. Other astronomical sources include BL Lacertae, 3C 66A Markarian 421 and Markarian 501. Various other sources exist that are not associated with known bodies. For example, the H.E.S.S. catalog contained 64 sources in November 2011.

The High Altitude Water Cherenkov Experiment or High Altitude Water Cherenkov Observatory is a gamma-ray and cosmic ray observatory located on the flanks of the Sierra Negra volcano in the Mexican state of Puebla at an altitude of 4100 meters, at 18°59′41″N97°18′30.6″W. HAWC is the successor to the Milagro gamma-ray observatory in New Mexico, which was also a gamma-ray observatory based around the principle of detecting gamma-rays indirectly using the water Cherenkov method.

The Large High Altitude Air Shower Observatory (LHAASO) is a gamma-ray and cosmic-ray observatory in Daocheng, in the Garzê Tibetan Autonomous Prefecture in Sichuan, China. It is designed to observe air showers triggered by gamma rays and cosmic rays. The observatory is at an altitude of 4,410 metres (14,470 ft) above sea level. Observations started in April 2019.

References

1 2 3 Ong, Rene (2006-09-09). Ultra High Energy Cosmic Ray Research with CASA-MIA. University of California, Los Angeles (UCLA). S2CID 39155837.
↑ Gaisser, T. K.; Staney, Todor; Halzen, F.; Long, W. F.; Zas, E. (1991-01-15). "Gamma-ray astronomy above 50 TeV with muon-poor showers". Physical Review D. 43 (2): 314–318. Bibcode:1991PhRvD..43..314G. doi:10.1103/PhysRevD.43.314. PMID 10013389.
↑ Gibbs, Kenneth G (1988-02-01). "The Chicago Air Shower Array (CASA)". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 264 (1): 67–73. Bibcode:1988NIMPA.264...67G. doi:10.1016/0168-9002(88)91104-7. ISSN 0168-9002.
↑ Ong, René A.; Cronin, James W.; Gibbs, Kenneth G.; Krimm, Hans A.; McKay, Timothy A.; Mascarenhas, Nicholas; Müller, Dietrich; Newport, Brian J.; Rosenberg, Leslie J.; Wiedenbeck, Mark E. (1990-03-01). "Design and performance of the Chicago Air Shower Array". Nuclear Physics B - Proceedings Supplements. 14 (1): 273–284. doi:10.1016/0920-5632(90)90432-T. ISSN 0920-5632.
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↑ Samorski, M.; Stamm, W. (1983). "Detection of 2 X 10 to the 15th to 2 X 10 to the 16th eV gamma-rays from Cygnus X-3". The Astrophysical Journal. 268: L17. doi: 10.1086/184021 . ISSN 0004-637X.
↑ Lloyd-Evans, J.; Coy, R. N.; Lambert, A.; Lapikens, J.; Patel, M.; Reid, R. J. O.; Watson, A. A. (1983). "Observation of γ rays >10 15 eV from Cygnus X-3". Nature. 305 (5937): 784–787. Bibcode:1983Natur.305..784L. doi:10.1038/305784a0. ISSN 1476-4687. S2CID 45448349.
↑ Borione, A.; Chantell, M. C.; Covault, C. E.; Cronin, J. W.; Fick, B. E.; Fowler, J. W.; Fortson, L. F.; Gibbs, K. G.; Green, K. D.; Newport, B. J.; Ong, R. A. (1997-02-15). "High statistics search for ultrahigh energy γ-ray emission from Cygnus X-3 and Hercules X-1". Physical Review D. 55 (4): 1714–1731. arXiv: astro-ph/9611117 . Bibcode:1997PhRvD..55.1714B. doi:10.1103/PhysRevD.55.1714. ISSN 0556-2821. S2CID 119107040.
↑ Borione, A.; Catanese, M. A.; Chantell, M. C.; Covault, C. E.; Cronin, J. W.; Fick, B. E.; Fortson, L. F.; Fowler, J. F.; Gibbs, K. G.; Glasmacher, M. A. K.; Green, K. D. (1997-05-20). "A Search for Ultra–High-Energy Gamma-Ray Emission from the Crab Nebula and Pulsar". The Astrophysical Journal. 481 (1): 313–326. Bibcode:1997ApJ...481..313B. doi: 10.1086/304042 . ISSN 0004-637X. S2CID 121666507.
↑ Catanese, M.; Borione, A.; Covault, C. E.; Cronin, J. W.; Fick, B. E.; Fortson, L. F.; Gibbs, K. G.; Glasmacher, M. A. K.; Green, K. D.; Kieda, D.; Matthews, J. (1996). "A Search for Ultrahigh-Energy Gamma Rays from EGRET-detected Active Galactic Nuclei Using CASA-MIA". The Astrophysical Journal. 469: 572. Bibcode:1996ApJ...469..572C. doi:10.1086/177806. ISSN 0004-637X.
↑ McKay, T. A.; Borione, A.; Catanese, M.; Covault, C. E.; Cronin, J. W.; Fick, B. E.; Gibbs, K. G.; Green, K. D.; Hauptfeld, S.; Kieda, D.; Krimm, H. A. (1993). "A Northern Sky Survey for Astrophysical Point Sources of 100 TeV Gamma Radiation". The Astrophysical Journal. 417: 742. Bibcode:1993ApJ...417..742M. doi:10.1086/173354. ISSN 0004-637X.
↑ Chantell, M. C.; Covault, C. E.; Cronin, J. W.; Fick, B. E.; Fortson, L. F.; Fowler, J. W.; Green, K. D.; Newport, B. J.; Ong, R. A.; Oser, S.; Catanese, M. A. (1997-09-08). "Limits on the Isotropic Diffuse Flux of Ultrahigh Energy $\ensuremath{\gamma}$ Radiation". Physical Review Letters. 79 (10): 1805–1808. arXiv: astro-ph/9705246 . doi:10.1103/PhysRevLett.79.1805. S2CID 119517410.
↑ Borione, A.; Catanese, M. A.; Chantell, M. C.; Covault, C. E.; Cronin, J. W.; Fick, B. E.; Fortson, L. F.; Fowler, J.; Glasmacher, M. A. K.; Green, K. D.; Kieda, D. B. (1998-01-20). "Constraints on Gamma-Ray Emission from the Galactic Plane at 300 TeV". The Astrophysical Journal. 493 (1): 175–179. arXiv: astro-ph/9703063 . Bibcode:1998ApJ...493..175B. doi: 10.1086/305096 . ISSN 0004-637X.
↑ Glasmacher, M. A. K.; Catanese, M. A.; Chantell, M. C.; Covault, C. E.; Cronin, J. W.; Fick, B. E.; Fortson, L. F.; Fowler, J. W.; Green, K. D; Kieda, D. B.; Matthews, J. (1999-05-01). "The cosmic ray energy spectrum between 1014 and 1016 eV". Astroparticle Physics. 10 (4): 291–302. Bibcode:1999APh....10..291G. doi:10.1016/S0927-6505(98)00070-X. ISSN 0927-6505.
↑ Glasmacher, M. A. K.; Catanese, M. A.; Chantell, M. C.; Covault, C. E.; Cronin, J. W.; Fick, B. E.; Fortson, L. F.; Fowler, J. W.; Green, K. D.; Kieda, D. B.; Matthews, J. (1999-10-01). "The cosmic ray composition between 1014 and 1016 eV". Astroparticle Physics. 12 (1): 1–17. Bibcode:1999APh....12....1G. doi:10.1016/S0927-6505(99)00076-6. ISSN 0927-6505.
↑ Fowler, J. W.; Fortson, L. F.; Jui, C. C. H.; Kieda, D. B.; Ong, R. A.; Pryke, C. L.; Sommers, P. (2001-03-01). "A measurement of the cosmic ray spectrum and composition at the knee". Astroparticle Physics. 15 (1): 49–64. arXiv: astro-ph/0003190 . Bibcode:2001APh....15...49F. doi:10.1016/S0927-6505(00)00139-0. ISSN 0927-6505. S2CID 2062778.

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[:1-1] 1 2 3 Ong, Rene (2006-09-09). Ultra High Energy Cosmic Ray Research with CASA-MIA. University of California, Los Angeles (UCLA). S2CID 39155837.

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