Detalles de publicación
PP 021087
The throughput calibration of the VERITAS telescopes
(1) Physics Department, Columbia University, New York, NY 10027,
USA
(2) Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA
02138, USA
(3) Department of Physics, Washington University, St. Louis, MO
63130, USA
(4) Physics Department, California Polytechnic State University, San
Luis Obispo, CA 94307, USA
(5) Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA
(6) Department of Physics and Astronomy, Barnard College, Columbia
University, NY 10027, USA
(7) Department of Physics and Astronomy, Purdue University, West
Lafayette, IN 47907, USA
(8) Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
(9) School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
(10) Department of Physics, California State University - East Bay, Hayward, CA 94542, USA
(11) DESY, Platanenallee 6, 15738 Zeuthen, Germany
(12) Physics Department, McGill University, Montreal, QC H3A 2T8,
Canada
(13) Santa Cruz Institute for Particle Physics and Department of Physics,
University of California, Santa Cruz, CA 95064, USA
(14) Department of Physics and Astronomy, University of Utah, Salt
Lake City, UT 84112, USA
(15) Department of Physics and Astronomy, University of Alabama,
Tuscaloosa, AL 35487, USA
(16) Department of Physics and Astronomy, University of Iowa, Van
Allen Hall, Iowa City, IA 52242, USA
(17) School of Physics, National University of Ireland Galway, University Road, Galway, Ireland
(18) Department of Physics, Engineering Physics, and Astronomy,
Queen’s University, Kingston, ON K7L 3N6, Canada
(19) Institute of Physics and Astronomy, University of Potsdam, 14476
Potsdam-Golm, Germany
(20) School of Physics, University College Dublin, Belfield, Dublin 4,
Ireland
(21) Department of Physical Sciences, Munster Technological University, Bishopstown, Cork, T12 P928, Ireland
(22) Department of Physics and Astronomy, University of California,
Los Angeles, CA 90095, USA
(23) Department of Physics and Astronomy, Iowa State University,
Ames, IA 50011, USA
(24) Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Av. Complutense, 40, E-28040 Madrid, Spain
(25) Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife,
Spain
(26) Universidad de La Laguna, Dept. Astrofísica, E-38206 La Laguna,
Tenerife, Spain
Context. The response of imaging atmospheric Cherenkov telescopes to incident {\gamma}-ray-initiated showers in the atmosphere changes as the telescopes age due to exposure to light and weather. These aging processes affect the reconstructed energies of the events and {\gamma}-ray fluxes. Aims. This work discusses the implementation of signal calibration methods for the Very Energetic Radiation Imaging Telescope Array System (VERITAS) to account for changes in the optical throughput and detector performance over time. Methods. The total throughput of a Cherenkov telescope is the product of camera-dependent factors, such as the photomultiplier tube gains and their quantum efficiencies, and the mirror reflectivity and Winston cone response to incoming radiation. This document summarizes different methods to determine how the camera gains and mirror reflectivity have evolved over time and how we can calibrate this changing throughput in reconstruction pipelines for imaging atmospheric Cherenkov telescopes. The implementation is validated against seven years of observations with the VERITAS telescopes of the Crab Nebula, which is a reference object in very-high-energy astronomy. Results. Regular optical throughput monitoring and the corresponding signal calibrations are found to be critical for the reconstruction of extensive air shower images. The proposed implementation is applied as a correction to the signals of the photomultiplier tubes in the telescope simulation to produce fine-tuned instrument response functions. This method is shown to be effective for calibrating the acquired {\gamma}-ray data and for recovering the correct energy of the events and photon fluxes. At the same time, it keeps the computational effort of generating Monte Carlo simulations for instrument response functions affordably low.