Bokeh Mirror Alignment for Cherenkov Telescopes

Abstract

Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures and high image intensities to map the faint Cherenkov light emitted from cosmic ray air showers onto their image sensors. Segmented reflectors fulfill these needs, and composed from mass production mirror facets they are inexpensive and lightweight. However, as the overall image is a superposition of the individual facet images, alignment remains a challenge. Here we present a simple, yet extendable method, to align a segmented reflector using its Bokeh. Bokeh alignment does not need a star or good weather nights but can be done even during daytime. Bokeh alignment optimizes the facet orientations by comparing the segmented reflectors Bokeh to a predefined template. The optimal Bokeh template is highly constricted by the reflector's aperture and is easy accessible. The Bokeh is observed using the out of focus image of a near by point like light source in a distance of about 10 focal lengths. We introduce Bokeh alignment on segmented reflectors and demonstrate it on the First Geiger-mode Avalanche Cherenkov Telescope (FACT) on La Palma, Spain.

accepted for publication in Astroparticle Physics

References in corpus (9)

• The First VERITAS Telescope
• Monte Carlo design studies for the Cherenkov Telescope Array
• Design and Operation of FACT -- The First G-APD Cherenkov Telescope
• The optical system of the H.E.S.S. imaging atmospheric Cherenkov telescopes, Part I: layout and components of the system
• The CAT Imaging Telescope for Very-High-Energy Gamma-Ray Astronomy
• A New Mirror Alignment System for the VERITAS Telescopes
• The Active Mirror Control of the MAGIC Telescope
• How to focus a Cherenkov telescope
• Normalized and Asynchronous Mirror Alignment for Cherenkov Telescopes

Cited by in corpus (6)

• The Medium Size Telescopes of the Cherenkov Telescope Array
• Normalized and Asynchronous Mirror Alignment for Cherenkov Telescopes
• Design and characterization of a single photoelectron calibration system for the NectarCAM camera of the medium-sized telescopes of the Cherenkov Telescope Array
• The Single Mirror Small Sized Telescope For The Cherenkov Telescope Array
• Mirror Position Determination for the Alignment of Cherenkov Telescopes
• Exploring one giga electronvolt cosmic gamma rays with a Cherenkov plenoscope capable of recording atmospheric light fields, Part 1: Optics