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Report number	arXiv:1703.01307
Title	Gamma-ray Observations Under Bright Moonlight with VERITAS
Related title	Gamma-ray Observations Under Bright Moonlight with VERITAS
Author(s)	Archambault, S. (McGill U.) ; Archer, A. (Washington U., St. Louis) ; Benbow, W. (Whipple Observ.) ; Bird, R. (UCLA) ; Bourbeau, E. (McGill U.) ; Bouvier, A. (UC, Santa Cruz) ; Buchovecky, M. (UCLA) ; Bugaev, V. (Washington U., St. Louis) ; Cardenzana, J. V (Iowa State U.) ; Cerruti, M. (Whipple Observ.) ; Ciupik, L. (Adler Planetarium, Chicago) ; Connolly, M.P. (Natl. U. of Ireland, Galway) ; Cui, W. (Purdue U. ; Tsinghua U., Beijing) ; Daniel, M.K. (Liverpool U.) ; Errando, M. (Washington U., St. Louis) ; Falcone, A. (Penn State U., Astron. Astrophys.) ; Feng, Q. (McGill U.) ; Finley, J.P. (Purdue U.) ; Fleischhack, H. (DESY, Zeuthen) ; Fortson, L. (Minnesota U.) ; Furniss, A. (Cal State, East Bay) ; Gillanders, G.H. (Natl. U. of Ireland, Galway) ; Griffin, S. (McGill U.) ; Hanna, D. (McGill U.) ; Hervet, O. (UC, Santa Cruz) ; Holder, J. (Delaware U., Bartol Inst.) ; Hughes, G. (Zurich, ETH) ; Humensky, T.B. (Columbia U.) ; Hütten, M. (DESY, Zeuthen) ; Johnson, C.A. (CERN) ; Kaaret, P. (Iowa U.) ; Kar, P. (Utah U.) ; Kertzman, M. (DePauw U.) ; Kieda, D. (Utah U.) ; Krause, M. (DESY, Zeuthen) ; Lang, M.J. (Natl. U. of Ireland, Galway) ; Maier, G. (DESY, Zeuthen) ; McArthur, S. (Purdue U.) ; Moriarty, P. (Natl. U. of Ireland, Galway) ; Mukherjee, R. (Barnard Coll.) ; Nieto, D. (Columbia U.) ; O'Brien, S. (University Coll., Dublin) ; Ong, R.A. (Chicago U., EFI) ; Otte, A.N. (Georgia Tech) ; Park, N. (Chicago U., EFI) ; Pohl, M. (DESY, Zeuthen ; Potsdam U.) ; Popkow, A. (UCLA) ; Pueschel, E. (University Coll., Dublin) ; Quinn, J. (University Coll., Dublin) ; Ragan, K. (McGill U.) ; Reynolds, P.T. (Cork Inst. Tech.) ; Richards, G.T. (Georgia Tech) ; Roache, E. (Whipple Observ.) ; Rulten, C. (Minnesota U.) ; Sadeh, I. (DESY, Zeuthen) ; Sembroski, G.H. (Purdue U.) ; Shahinyan, K. (Minnesota U.) ; Staszak, D. (Chicago U., EFI) ; Telezhinsky, I. (DESY, Zeuthen ; Potsdam U.) ; Trepanier, S. (McGill U.) ; Wakely, S.P. (Chicago U., EFI) ; Weinstein, A. (Iowa State U.) ; Wilcox, P. (Iowa U.) ; Williams, D.A. (UC, Santa Cruz) ; Zitzer, B. (Argonne)
Publication	2017
Imprint	2017-03-03
Number of pages	19
In:	Astropart. Phys. 91 (2017) 34-43
DOI	10.1016/j.astropartphys.2017.03.001
Subject category	astro-ph.IM ; Astrophysics and Astronomy
Abstract	Imaging atmospheric Cherenkov telescopes (IACTs) are equipped with sensitive photomultiplier tube (PMT) cameras. Exposure to high levels of background illumination degrades the efficiency of and potentially destroys these photo-detectors over time, so IACTs cannot be operated in the same configuration in the presence of bright moonlight as under dark skies. Since September 2012, observations have been carried out with the VERITAS IACTs under bright moonlight (defined as about three times the night-sky-background (NSB) of a dark extragalactic field, typically occurring when Moon illumination > 35%) in two observing modes, firstly by reducing the voltage applied to the PMTs and, secondly, with the addition of ultra-violet (UV) bandpass filters to the cameras. This has allowed observations at up to about 30 times previous NSB levels (around 80% Moon illumination), resulting in 30% more observing time between the two modes over the course of a year. These additional observations have already allowed for the detection of a flare from the 1ES 1727+502 and for an observing program targeting a measurement of the cosmic-ray positron fraction. We provide details of these new observing modes and their performance relative to the standard VERITAS observations.
Copyright/License	Elsevier B.V. (License: CC-BY-NC-SA-4.0)

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