[Paper Review] Next generation of IACT arrays: scientific objectives versus energy domains

F. Aharonian|arXiv (Cornell University)|Nov 4, 2005

Particle Detector Development and Performance4 citations

TL;DR

This paper proposes a next-generation Imaging Atmospheric Cherenkov Telescope (IACT) array spanning four energy domains—multi-GeV to sub-PeV—featuring a 10−14 erg/cm²/s flux sensitivity in the TeV band, enabled by stereoscopic arrays of 10m-diameter telescopes. It advocates for complementary instruments: a deep-sky survey array for TeV sources, a low-threshold array for GeV gamma rays (5@5 concept), and large-field-of-view detectors for monitoring transient phenomena.

ABSTRACT

Several key motivations and perspectives of ground based gamma-ray astronomy are discussed in the context of the specifics of detection techniques and scientific topics/objectives relevant to four major energy domains -- very-low or \ extit{multi-GeV} ($E \\leq$ 30 GeV), low or \ extit{sub-TeV} (30 GeV - 300 GeV), high or \ extit{TeV} (300 GeV - 30 TeV), and very-high or \ extit{sub-PeV} ($E \\geq$ 30 TeV) intervals -- to be covered by the next generation of IACT arrays.

Motivation & Objective

• To define the scientific objectives and technical requirements for next-generation IACT arrays across four energy domains: multi-GeV, sub-TeV, TeV, and sub-PeV.
• To establish a 10−14 erg/cm²/s flux sensitivity in the 0.1–10 TeV range as a primary goal, enabling deep surveys of galactic and extragalactic TeV sources.
• To enable detection of faint and extended TeV sources, including weak HESS sources and diffuse Galactic emission, through improved angular resolution and sensitivity.
• To extend IACT capabilities to the multi-GeV regime via low-threshold arrays (e.g., 5@5 concept) to study highly variable sources like blazars and GRBs at z ≥ 5.
• To develop large-field-of-view ground-based detectors (≥1 sr) for all-sky monitoring of transient and variable VHE gamma-ray phenomena, complementing GLAST and neutrino detectors.

Proposed method

• Utilize stereoscopic arrays of 10m-diameter IACTs to achieve high detection efficiency and accurate reconstruction of shower direction and energy, enabling 10−14 erg/cm²/s sensitivity at 1 TeV.
• Implement advanced focal plane imagers with high quantum efficiency and robotic operation at high-altitude sites to optimize performance across energy ranges.
• Adopt the 5@5 concept—five 10m telescopes at 5000 m altitude—to reduce energy threshold to a few GeV, enabling detection of GeV-band transients.
• Explore three large FoV techniques: refractive optics-based imaging Cherenkov telescopes, arrays of 15° FoV IACTs, and high-altitude particle/water Cherenkov arrays.
• Leverage GLAST as a trigger and guide for targeted observations with small-FoV IACTs, enabling follow-up of transient events detected in the GeV band.
• Integrate large-field-of-view detectors with IACT arrays to enable simultaneous monitoring of a significant fraction of the sky (≥1 sr) for transient phenomena.

Experimental results

Research questions

• RQ1 What scientific objectives can be achieved by extending IACT arrays to cover the full energy range from multi-GeV to sub-PeV gamma rays?
• RQ2 How can a 10−14 erg/cm²/s flux sensitivity be achieved in the 0.1–10 TeV range using stereoscopic IACT arrays?
• RQ3 What are the technical and scientific advantages of low-threshold IACT arrays (e.g., 5@5) for detecting highly variable or transient GeV-TeV sources?
• RQ4 How can large-field-of-view ground-based detectors complement satellite missions like GLAST and km³-scale neutrino detectors in monitoring transient VHE phenomena?
• RQ5 What is the optimal design for next-generation IACT arrays to enable deep all-sky surveys and high-time-resolution monitoring of variable sources?

Key findings

• A 10−14 erg/cm²/s flux sensitivity at 1 TeV is achievable with stereoscopic IACT arrays of 10m-diameter telescopes, enabling detection of galactic sources with luminosities as low as 10³² erg/s at 10 kpc.
• The 10−14 erg/cm²/s sensitivity allows detection of weak HESS sources in less than one hour of observation, with angular resolution of 1–2 arcminutes.
• The 5@5 concept—five 10m telescopes at 5000 m altitude—can reduce the energy threshold to a few GeV, enabling studies of highly variable sources like blazars and GRBs at z ≥ 5.
• Large-field-of-view detectors (≥1 sr) are essential for monitoring transient VHE phenomena, such as microquasars and GeV-TeV counterparts of classical GRBs.
• High-altitude particle arrays and water Cherenkov detectors have demonstrated feasibility, offering a low-technology path to large FoV coverage.
• The combination of IACT arrays with GLAST provides complementary capabilities: GLAST for wide-field monitoring and IACTs for high-time-resolution follow-up of transients.