Telescope Array Site Research Articles

Detection limits and trigger rates for ultra-high energy cosmic ray detection with the EUSO-TA ground-based fluorescence telescope

EUSO-TA is a ground-based fluorescence telescope built to validate the design of ultra-high energy cosmic ray fluorescence detectors to be operated in space with the technology developed within the Joint Exploratory Missions for Extreme Universe Space Observatory (JEM-EUSO) program. It operates at the Telescope Array (TA) site in Utah, USA. With an external trigger provided by the Black Rock Mesa fluorescence detectors of the Telescope Array experiment, with EUSO-TA we observed air-showers from ultra-high energy cosmic rays, as well as laser events from the Central Laser Facility at the TA site and from portable lasers like the JEM-EUSO Global Light System prototype. Since the Black Rock Mesa fluorescence detectors have a ∼30 times larger field of view than EUSO-TA, they allow a primary energy reconstruction based on the observation of a large part of the shower evolution, including the shower maximum, while EUSO-TA observes only a part of it, usually far away from the maximum. To estimate the detection limits of EUSO-TA in energy and distance, a method was developed to re-scale their energy, taking into account that EUSO-TA observes only a portion of the air-showers. The method was applied on simulation sets with showers with different primaries, energy, direction, and impact point on the ground, as well as taking into account the experimental environment. EUSO-TA was simulated with an internal trigger and different elevation angles and electronics. The same method was then applied also to real measurements and compared to the simulations. In addition, the method can also be used to estimate the detection limits for experiments that are operated at high altitudes and in most cases can see the maximum of the showers. This was done for EUSO-SPB1, an instrument installed on a super-pressure balloon. Finally, the expected detection rates for EUSO-TA were also assessed using the prepared simulated event sets. The rates correspond to a few detections per recording session of 30 h of observation, depending on the background level and the configuration of the detector.

Potential for atmospheric monitoring using FAST telescopes

The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a design for a next-generation ground-based ultra-high energy cosmic ray observatory, addressing the requirements for a large-area, low-cost detector suitable for measuring the properties of the highest energy cosmic rays with an unprecedented aperture. Three telescope prototypes are installed nearby the fluorescence telescopes of Telescope Array and one prototype is located at the Pierre Auger Observatory. Apart from detecting cosmic ray showers, the FAST prototypes offer the possibility of detecting laser pulses from atmospheric facilities such as CLF. The first part of the contribution describes the theoretical modeling of the photon scattering processes for different atmospheric models, and the raytracing of photons from the laser shot to and inside the FAST telescope. Simulations will be performed for different types of scattering conditions dependent on e.g. the size of the scattering centers or other parameters such as humidity. The ultimate goal is to create a software tool simulating the measured signals in the FAST telescopes from distant laser shots with proper treatment of light propagation trough the atmosphere and trough the detector. Such simulation toolkit for FAST prototypes at the Pierre Auger Observatory will benefit from existing attempts done for the Telescope Array site. Another part of the contribution will concern the real data of the observed CLF shots by the FAST prototypes both at the Pierre Auger Observatory and Telescope Array. Moreover, we can focus on the comparison of measured CLF shots by FAST prototype with the available data recorded by the full-scale fluorescence telescopes of the Pierre Auger Observatory.

Extreme Universe Space Observatory on a Super Pressure Balloon 1 calibration: from the laboratory to the desert

The Extreme Universe Space Observatory on a Super Pressure Balloon 1 (EUSO-SPB1) instrument was launched out of Wanaka, New Zealand, by NASA in April, 2017 as a mission of opportunity. The detector was developed as part of the Joint Experimental Missions for the Extreme Universe Space Observatory (JEM-EUSO) program toward a space-based ultra-high energy cosmic ray (UHECR) telescope with the main objective to make the first observation of UHECRs via the fluorescence technique from suborbital space. The EUSO-SPB1 instrument is a refractive telescope consisting of two 1m$^2$ Fresnel lenses with a high-speed UV camera at the focal plane. The camera has 2304 individual pixels capable of single photoelectron counting with a time resolution of 2.5$\mu$s. A detailed performance study including calibration was done on ground. We separately evaluated the properties of the Photo Detector Module (PDM) and the optical system in the laboratory. An end-to-end test of the instrument was performed during a field campaign in the West Desert in Utah, USA at the Telescope Array (TA) site in September 2016. The campaign lasted for 8 nights. In this article we present the results of the preflight laboratory and field tests. Based on the tests performed in the field, it was determined that EUSO-SPB1 has a field of view of 11.1$^\circ$ and an absolute photo-detection efficiency of 10%. We also measured the light flux necessary to obtain a 50% trigger efficiency using laser beams. These measurements were crucial for us to perform an accurate post flight event rate calculation to validate our cosmic ray search. Laser beams were also used to estimated the reconstruction angular resolution. Finally, we performed a flat field measurement in flight configuration at the launch site prior to the launch providing a uniformity of the focal surface better than 6%.

Atmospheric transparency at TA site using Central Laser Facility

The Telescope Array (TA) experiment has three fluorescence detector (FD) stations to measure fluorescence light emitted from extensive air showers, especially produced by Ultra High Energy Cosmic Rays(UHECRs). These fluorescence light is attenuated and decreased by aerosols in the atmosphere during their propagation to the FD. Measuring and calibrating the atmospheric attenuation is necessary to estimate energy of primary cosmic rays. The central Laser Facility (CLF) consists of a laser of wavelength of 355 nm, and emits beam vertically with 10 Hz, every half-hour. The atmospheric transparency in terms of the Vertical Atmospheric Optical Depth (VAOD) is measured with the CLF every 30 minutes during FD observation. The CLF is located at the center of three FD stations and observes the atmospheric transparency of the TA site. We calculated VAOD τAS(5km) at the BR station using 1853 events of the CLF laser from January 2012 to September 2016. We found that the median of VAOD at 5 km height from the ground is . We also found a seasonal variation of VAOD using the same data.

Air shower observation by a simple structured Fresnel lens telescope with a single pixel for the next generation of ultra-high-energy cosmic ray observatories

Improved statistics and observations sensitive to mass composition are required to clarify the origin of ultra-high-energy cosmic rays (UHECRs). Inevitably, in the future UHECR observatories will have to be expanded due to the small flux; however, such upgrades will be expensive with the detectors currently in use. Hence, we are developing a new fluorescence detector for UHECR observation. The proposed fluorescence detector, called a cosmic ray air fluorescence Fresnel lens telescope (CRAFFT), has an extremely simple structure and can observe the longitudinal development of an air shower. Furthermore, CRAFFT has the potential to significantly reduce costs for the realization of a huge observatory for UHECR research. We deployed four CRAFFT detectors at the Telescope Array site and conducted a test observation. We have successfully observed ten air shower events using CRAFFT. Thus, CRAFFT can be a solution to help realize the next generation of UHECR observatories.

Results of the missions within JEM-EUSO program

The JEM-EUSO program includes several missions employing fluorescence detectors to make a proof-of-principle of the UHECR observation from space and to raise the technological level of the instrumentation to be employed in a space mission like K-EUSO and POEMMA. EUSO-TA, installed at the Telescope Array (TA) site in Utah in 2013, has already detected 9 UHECRs in coincidence with TA Fluorescence Detector. EUSO-Balloon flew on board a stratospheric balloon in 2014. It measured the UV intensity on forests, lakes and the city of Timmins as well as proved the observation of UHECR-like events by shooting laser tracks. EUSO-SPB was launched on board a Super Pressure Balloon (SPB) in 2017. It proved the functionality of all the subsystems of the telescope on a long term; observed the UV emission on oceans and had a self-trigger system to detect UHECRs. A more ambitious mission (EUSOSPB2) is planned. TUS, on board the Lomonosov satellite in orbit since 2016, has detected a few interesting signals in the UHECR trigger-mode. Mini-EUSO is in a final phase of integration and will be installed inside the International Space Station (ISS) in 2019. The main results obtained so far by these experiments are summarized.

Detection of ultra-high energy cosmic ray air showers by Cosmic Ray Air Fluorescence Fresnel lens Telescope for next generation

In the future, ultra-high energy cosmic ray (UHECR) observatory will be expanded due to the small flux. Then, cost reduction is useful strategy to realize a huge scale observatory. For this purpose, we are developing a simple structure cosmic ray detector named as Cosmic Ray Air Fluorescence Fresnel-lens Telescope (CRAFFT). We deployed CRAFFT detectors at the Telescope Array site and performed a test observation. We have successfully observed UHECR air showers. We will report the status and the result of the test observation.

Cloud monitoring system at Telescope Array site by Visible Fisheye CCD

The Telescope Array (TA) is an international experiment studying ultra-high energy cosmic rays. TA uses the fluorescence detection technique to observe cosmic rays. In order to estimate the energy of cosmic rays with a fluorescence detector (FD), it is necessary to measure the condition of the observation area. Clouds affect the accuracy of the energy estimation. It is necessary to measure the existence of clouds and their direction in the Field Of View (FOV) of the FD. We developed a cloud monitoring system to measure the night sky weather using a CCD camera. In this report, we present our progress on our CCD cloud monitoring system.

The Detection of UHECRs with the EUSO-TA Telescope

EUSO-TA is a cosmic ray detector developed by the JEM-EUSO (Joint Experiment Missions for Extreme Universe Space Observatory) Collaboration, observing during nighttime the fluorescence light emitted along the path of extensive air showers in the atmosphere. It is installed at the Telescope Array site in Utah, USA, in front of the fluorescence detector station at Black Rock Mesa. It serves as a ground-based pathfinder experiment for future space-based missions. EUSO-TA has an optical system with two Fresnel lenses and a focal surface with 6 × 6 multi-anode photomultiplier tubes with 64 channels each, for a total of 2304 channels. The overall field of view is ∼10.6°× 10.6°. This detector technology allows the detection of cosmic ray events with high spatial resolution, having each channel a field of view of about ∼0.2° × 0.2° and a temporal resolution of 2.5 µs. First observations of ultra-high energy cosmic rays revealed the cosmic ray detection capability of EUSO-TA. The foreseen upgrade of EUSO-TA will improve the efficiency of the detector and will increase the statistics of detected events. In this work we present recent results of the detection capability of EUSO-TA and its limits. Moreover, other results about the analysis of laser pulses, stars and meteors will be discussed.

Results from the first missions of the JEM-EUSO program

The origin and nature of Ultra-High Energy Cosmic Rays (UHECRs) remain unsolved in contemporary astroparticle physics. To give an answer to these questions is rather challenging because of the extremely low flux of a few per km2 per century at extreme energies such as E > 5 × 1019 eV. The objective of the JEM-EUSO program, Extreme Universe Space Observatory, is the realization of a space mission devoted to scientific research of cosmic rays of highest energies. Its super-wide-field telescope will look down from space onto the night sky to detect UV photons emitted from air showers generated by UHECRs in the atmosphere. The JEM-EUSO program includes different missions using fluorescence detectors to make a proof-of-principle of the UHECR observation from space and to raise the technological level of the instrumentation to be employed in a space mission. EUSO-TA, installed at the Telescope Array site in Utah in 2013, is in operation. It has already detected 9 UHECRs in coincidence with Telescope Array fluorescence detector at Black Rock Mesa. EUSO-Balloon flew on board a stratospheric balloon in August 2014. It measured the UV intensity on forests, lakesandthecityofTimminsaswellasprovedtheobservationofUHECR-likeeventsbyshootinglasertracks. EUSO-SPB was launched on board a super pressure balloon on April 25th and flew for 12 days. It proved the functionality of all the subsystems of the telescope on a typical duration of a balloon flight; observed the UV emission on oceans and has a self-trigger system to observe UHECRs with energy E > 3×1018 eV. TUS, the Russian mission on board the Lomonosov satellite in orbit since April 28th 2016, is now included in the JEMEUSO program and has detected so far in the UHECR trigger-mode a few interesting signals. Mini-EUSO is in its final phase of integration in Italy, where several performance tests are being held. Mini-EUSO will be installed inside the International Space Station (ISS) in 2019. The main results obtained so far by such missions are summarized and put in prospect of future space detectors such as K-EUSO and POEMMA.

EUSO-TA – First results from a ground-based EUSO telescope

EUSO-TA is a ground-based telescope, installed at the Telescope Array (TA) site in Black Rock Mesa, Utah, USA. This is the first detector to successfully use a Fresnel lens based optical system and multi-anode photomultipliers (64 channels per tube, 2304 channels encompassing a 10.6° × 10.6° field of view) for detection of Ultra High Energy Cosmic Rays (UHECR). The telescope is located in front of one of the fluorescence detectors of the TA experiment. Since its installation in 2013, the detector has observed several ultra-high energy cosmic ray events and, in addition, meteors. The limiting magnitude of 5.5 on summed frames ( ∼ 3 ms) has been established. Measurements of the UV night sky emission in different conditions and moon phases and positions have been completed. The performed observations serve as a proof of concept for the future application of this detector technology.

EUSO-TA, a JEM-EUSO pathfinder at the Telescope Array site

EUSO-TA is one of the prototypes of the JEM-EUSO space telescope, realized in the framework of the EUSO project. Its aims are to calibrate the detector response, test its performance in air and vacuum, raise the technological readiness level of some of the components and improve our knowledge of the various detector systems.EUSO-TA is located at the Telescope Array (TA) site in Black Rock Mesa, Utah, USA and is mainly devoted to study the detector response in conjunction with the TA fluorescence detector. The telescope is housed in a shed located in front of one of the fluorescence detectors of the Telescope Array experiment, pointing in the direction of the ELS (Electron Light Source) and CLF (Central Laser Facility), i.e. the artificial light sources at the Telescope Array site.The detector consists of two Fresnel lenses, 1×1 □m each, with a field of view of 11°×11°, able to focus the ultraviolet light generated by cosmic-ray showers as well as from artificial sources, on a focal surface identical to the ones that will be employed in JEM-EUSO.

The FAST Project - A Next Generation UHECR Observatory

We present a concept for large-area, low-cost detection of ultrahigh-energy cosmic rays (UHECRs) with a Fluorescence detector Array of Single-pixel Telescopes (FAST), addressing the requirements for the next generation of UHECR experiments. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. We report on the first results of a FAST prototype installed at the Telescope Array (TA) site, consisting of a single 200 mm photomultiplier tube (PMT) at the focal plane of a 1 m2 Fresnel lens system taken from the prototype of the JEM-EUSO experiment. We also report on the status of the full-scale FAST prototype soon to be installed at the TA site, comprising a segmented spherical mirror of 1.6 m diameter and a 2 × 2 PMT camera.

The JEM-EUSO Program

The Extreme Universe Space Observatory on-board the Japanese Experiment Module (JEM-EUSO) of the International Space Station (ISS), is a space mission that aims to unveiling the nature and the origin of the Ultra High Energy Cosmic Rays (UHECRs) and to address basic problems of fundamental physics at extreme energies. The instrument is designed to measure the arrival direction, the energy and, possibly, the nature of these particles. Basically, it consists of a wide Field of View (FoV) telescope, based on Fresnel lenses, that looks down from the ISS during night-time to detect UV photons (fluorescence and Cherenkov photons) emitted from air showers. An infrared camera and an atmosphere monitoring system improve the performance of the instrument. The program is proceeding in different steps. While the JEM-EUSO mission is being improved to allow the use of the new carrier Space-X Dragon, the project K-EUSO, a mirror-based telescope to be placed on the Russian module of the ISS, conceived as an improvement of the KLYPVE experiment already approved by the Russian Space Agency Roscosmos, modified with EUSO technology, is in the stage of final definition. Meanwhile, a program of test experiments, pathfinders of the main mission, has been developed: the first, EUSO-Balloon, successfully flew on board a stratospheric balloon in Canada to measure the fluorescence background from the top of the Atmosphere; a second, EUSO-TA on ground, is in operation at the Telescope Array site in Utah. Next steps include: a) Mini-EUSO, approved by Roscosmos and the Italian Space Agency ASI, a small, compact UV telescope to be installed inside the Russian Module of the ISS to measure the UV background from Earth and b) a long duration Super Pressure Balloon Flight (EUSO-SPB) to be flown from New Zealand to observe EAS (Extensive Air Showers) from stratospheric atmosphere altitudes. Scientific, technical and programmatic aspects of all these EUSO-like projects are described.

Detection of ultra-high energy cosmic ray showers with a single-pixel fluorescence telescope

We present a concept for large-area, low-cost detection of ultra-high energy cosmic rays (UHECRs) with a Fluorescence detector Array of Single-pixel Telescopes (FAST), addressing the requirements for the next generation of UHECR experiments. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. We report first results of a FAST prototype installed at the Telescope Array site, consisting of a single 200 mm photomultiplier tube at the focal plane of a 1 m2 Fresnel lens system taken from the prototype of the JEM-EUSO experiment. The FAST prototype took data for 19 nights, demonstrating remarkable operational stability. We detected laser shots at distances of several kilometers as well as 16 highly significant UHECR shower candidates.

EUSO-TA prototype telescope

EUSO-TA is one of the prototypes developed for the JEM-EUSO project, a space-based large field-of-view telescope to observe the fluorescence light emitted by cosmic ray air showers in the atmosphere. EUSO-TA is a ground-based prototype located at the Telescope Array (TA) site in Utah, USA, where an Electron Light Source and a Central Laser Facility are installed. The purpose of the EUSO-TA project is to calibrate the prototype with the TA fluorescence detector in presence of well-known light sources and cosmic ray air showers. In 2015, the detector started the first measurements and tests using the mentioned light sources have been performed successfully. A first cosmic ray candidate has been observed, as well as stars of different magnitude and color index. Since Silicon Photo-Multipliers (SiPMs) are very promising for fluorescence telescopes of next generation, they are under consideration for the realization of a new prototype of EUSO Photo Detector Module (PDM). The response of this sensor type is under investigation through simulations and laboratory experimentation.

Ground-based tests of JEM-EUSO components at the Telescope Array site, “EUSO-TA”

We are conducting tests of optical and electronics components of JEMEUSO at the Telescope Array site in Utah with a ground-based “EUSO-TA” detector. The tests will include an engineering validation of the detector, cross-calibration of EUSO-TA with the TA fluorescence detector and observations of air shower events. Also, the proximity of the TA’s Electron Light Source will allow for convenient use of this calibration device. In this paper, we report initial results obtained with the EUSO-TA telescope.

Lightning Detection at the Telescope Array Cosmic Ray Observatory

It has been known for over a decade that x-ray and gamma radiation (» 100 keV to 10 MeV) is emitted by lightning strikes. This phenomenon has been observed by ground-and space-based detectors in association with both natural and induced lightning. Recently physicists stud ying data collected by the 700 km 2 Telescope Array (TA) Cosmic Ray Observatory in Western Utah, U.S.A. have observed gamma radiation in coincidence with lightning strikes. Using cosmic ray air shower rec onstruction techniques, these gamma ray showers can be pointed back to their origin in the Earth's atmos phere. In response to these observations, a Lightning Mapping Array(LMA) consisting of ten autonomous VHF detectors was recently deployed at the Telescope Array site. The LMA detectors record impulsive radiation from lightning with 10 microsecond timing accuracy in order to create 3-dimensional GPS-timed reconstruction of a lightning strike. In addition to contributing to the study of gamma ray generation by lightning, The TA/LMA merger will also be the perfect instrument to search for evidence of a more speculative phenomena: The seeding of lightning strikes by cosmic ray air showers. There have been suggestions that high energy particles may be emitted by natural or triggered light- ning interactions in the Earth's atmosphere (3). Large bursts of such par ticles may in turn mimic extensive air showers. A direct observation of this effect was recently made using the Telescope Array cosmic ray observatory, as described below. Here, we describe our plan to install a permanent Lightning Mapping Arrayat the Telescope Array site. The combination of TA and LMA detectors will be used in an attempt to understand how lightning strikes produce air shower-like bursts of high energy particles. Also, th is detector will be the ideal config- uration to search for evidence of cosmic rays triggering lightning strikes. T hus the TA/LMA project has among its scientific objectives the study of a novel known phenomenon in unp recedented detail, and the search for evidence of an as-yet unobserved effect.

Search for molecular bremsstrahlung radiation signals in Ku band with coincidental operations of radio telescopes with air shower detectors

Microwave radiation from extensive air showers is expected to provide a new technique to observe UHECR. We developed three set of radio telescopes in Osaka, in Kobe and at Telescope Array site in Utah, USA. In Osaka, we are coincidentally operating two Ku band radio telescopes with an air shower array which consists of nine plastic scintillators with about 10 m separation. In Kobe, we have started the operation of twelve radio telescopes of 1.2 m diameter in March 2012. In Utah, we installed two telescopes just beside the Black Rock Mesa fluorescence detector (FD) station of the Telescope Array experiment, and we operated the radio telescopes coincidentally with FD event triggers. We report the experimental setups and the results of these measurements.

Calibration and testing of a prototype of the JEM-EUSO telescope on Telescope Array site

Aim of the TA-EUSO project is to install a prototype of the JEM-EUSO telescope on the Telescope Array site in Black Rock Mesa, Utah and perform observation of natural and artificial ultraviolet light. The detector consists of one Photo Detector Module (PDM), identical to the 137 present on the JEM- EUSO focal surface. Each PDM is composed by 36 Hamamatsu multi-anode photomultipliers (64 channels per tube), for a total of 2304 channels. Front-End readout is performed by 36 ASICS, with trigger and readout tasks performed by two FPGA boards that send the data to a CPU and storage system. Two, 1 meter side square Fresnel lenses provide a field-of-view of 8 degrees. The telescope will be housed in a container located in front of the fluorescence detector of the Telescope Array collaboration, looking in the direction of the ELF (Electron Light Source) and CLF (Central Laser Facility). Aim of the project is to calibrate the response function of the EUSO telescope with the TA fluorescence detector in presence of a shower of known intensity and distribution. An initial run of about six months starting from end 2012 is foreseen, during which we expect to observe, triggered by TA electronics, a few cosmic ray events which will be used to further refine the calibration of the EUSO-Ground with TA. Medium term plans include the increase of the number of PDM and therefore the field of view.