[Paper Review] The Fluorescence detector Array of Single-pixel Telescopes: Contributions to the 35th International Cosmic Ray Conference (ICRC 2017)

Toshihiro Fujii, M. Malacari+18 more|arXiv (Cornell University)|Aug 4, 2017

Astrophysics and Cosmic Phenomena1 references11 citations

TL;DR

The Fluorescence detector Array of Single-pixel Telescopes (FAST) proposes a low-cost, large-aperture ground-based UHECR detection system using a few large PMTs (four 200 mm) focused by a segmented 1.6 m spherical mirror to cover a 25°×25° field of view. First results from the full-scale prototype installed at the Telescope Array site in Utah demonstrate successful detection of UV LED flashers, distant UV lasers, and time-coincident UHECR showers, confirming operational stability and performance in real-world conditions.

ABSTRACT

Contributions of the Fluorescence detector Array of Single-pixel Telescopes (FAST) to the 35th International Cosmic Ray Conference, 12-20 July 2017, Busan, Korea

Motivation & Objective

• Address the need for large-aperture, low-cost UHECR observatories to improve statistics at ultrahigh energies.
• Develop a scalable, ground-based fluorescence telescope design using few large PMTs and compact optics.
• Demonstrate feasibility and stability of the FAST concept in real field conditions with a full-scale prototype.
• Enable future deployment of large arrays of these telescopes to study the origin and composition of ultrahigh-energy cosmic rays.

Proposed method

• Deploy a full-scale FAST prototype featuring a 1.6 m segmented spherical mirror and four 200 mm PMTs in a 2×2 matrix at the focal plane.
• Use a UV band-pass filter (ZWB3) with 1 m² aperture to isolate fluorescence light in the 300–400 nm range.
• Implement a dual-laser alignment system: one at 2f distance for initial mirror alignment and one near the optical axis for Bokeh-based fine-tuning.
• Utilize an astronomical camera with fast f-number and 15° FOV to align the telescope’s optical axis via star tracking and astrometry.net software.
• Conduct data acquisition using UV LED flashers, distant vertical UV lasers, and time-coincident UHECR events with the Telescope Array FD.
• Apply geometric and photometric calibration techniques to ensure accurate pointing and signal reconstruction.

Experimental results

Research questions

• RQ1 Can a single-pixel fluorescence telescope design with a few large PMTs achieve sufficient sensitivity and angular resolution for UHECR detection?
• RQ2 Does the full-scale FAST prototype maintain operational stability under real field conditions, including temperature variations and background light?
• RQ3 Can the FAST prototype detect and reconstruct artificial UV light sources and distant UV lasers with high fidelity?
• RQ4 Is the FAST prototype capable of identifying time-coincident UHECR showers with the existing Telescope Array fluorescence detector?
• RQ5 Can the mirror alignment technique using dual laser sources achieve sub-arcsecond pointing accuracy?

Key findings

• The full-scale FAST prototype successfully detected UV LED flashers, confirming the system’s ability to capture controlled light pulses with high signal-to-noise ratio.
• The telescope detected a distant vertical UV laser beam at a range of ~1 km, demonstrating effective long-range light collection and pointing accuracy.
• The prototype recorded time-coincident UHECR shower signals with the Telescope Array fluorescence detector, validating its capability to detect real cosmic ray events.
• The mirror alignment procedure using 2f and Bokeh techniques achieved sub-arcsecond pointing accuracy, with misalignment < 0.01° at telescope-screen distances > 200 m.
• The system demonstrated robust operational stability under field conditions, including temperature fluctuations, night sky background variations, and power interruptions.
• The prototype’s 25°×25° field of view, covered by four 200 mm PMTs, proved sufficient for detecting extensive air shower fluorescence light with high efficiency.