View source for VERITAS

{{Short description|Ground-based gamma-ray observatory}}
{{for multi|the planned NASA Venus orbiter|VERITAS (spacecraft)|other uses|Veritas (disambiguation)}}
{{Use American English|date=June 2021}}
{{Use dmy dates|date=June 2021}}

{{Infobox telescope
|name=VERITAS
|alt=Very Energetic Radiation Imaging Telescope Array System
}}

'''VERITAS''' ('''Very Energetic Radiation Imaging Telescope Array System''') is a major ground-based [[gamma ray|gamma-ray]] observatory with an array of four 12 meter optical reflectors for gamma-ray astronomy in the [[electronvolt|GeV]] – TeV [[photon energy]] range. VERITAS uses the [[IACT|Imaging Atmospheric Cherenkov Telescope]] technique to observe gamma rays that cause [[particle shower]]s in Earth's atmosphere that are known as extensive [[Air shower (physics)|air showers]]. The VERITAS array is located at the [[Fred Lawrence Whipple Observatory]], in southern [[Arizona]], [[United States]]. The VERITAS reflector design is similar to the earlier Whipple 10-meter gamma-ray telescope, located at the same site, but is larger in size and has a longer focal length for better control of optical aberrations. VERITAS consists of an array of imaging telescopes deployed to view atmospheric Cherenkov showers from multiple locations to give the highest sensitivity in the 100 GeV – 10 TeV band (with sensitivity from 50 GeV to up to 50 TeV). This very high energy observatory, completed in 2007, effectively complements the Large Area Telescope (LAT) of the [[Fermi Gamma-ray Space Telescope]] due to its larger collection area as well as coverage in a higher energy band.

== Specifications and design ==
VERITAS is constructed of four 12 m diameter [[IACT|Imaging Atmospheric Cherenkov Telescope]]s with an approximate separation of {{cvt|100|m}} between each adjacent telescope.<ref name="Relocation">{{cite arXiv |eprint=0912.3841|last1=Perkins|first1=Jeremy S.|title=VERITAS Telescope 1 Relocation: Details and Improvements|last2=Maier|first2=Gernot|author3=The VERITAS Collaboration|class=astro-ph.IM|date=2009}}</ref> Each telescope comprises a large, steerable optical reflector and a high-speed [[photomultiplier tube]] camera. Multiple telescopes in an array are needed for stereoscopic observations of the Cherenkov light produced in extensive air showers. These stereoscopic observations allow precise reconstruction of the [[particle shower]] geometry, thus giving greatly improved angular and energy resolution compared to a single telescope. The angular direction of the incoming shower is determined by finding the central axis of the spread of the shower on each telescope and tracing those axes until they cross. The intersection of these axes determines the incoming direction of the primary particle (cosmic ray or gamma ray) that initiated the air shower in the upper atmosphere. It also determines the shower core position, i.e. the extrapolated position of the primary particle on the ground had it not interacted. The energy of the primary particle is determined from the total amount of Cherenkov light measured in each telescope, along with the distance of that telescope from the shower core.

Each of the individual telescopes has a 12 m diameter aperture and a 3.5 degree field of view. The telescopes are built on a Davies-Cotton optical design, which uses a spherical reflector and is straight forward to construct and align. This design does cause some time spread in the arrival of Cherenkov photons at the camera, but this spread is small (~ 4 nanoseconds).<ref name="Concept2">{{cite journal |last1=Krennrich|first1=F.|last2=Bond|first2=I. H.|last3=Boyle|first3=P. J.|last4=Bradbury|first4=S. M.|last5=Buckley|first5=J. H.|last6=Carter-Lewis|first6=D.|last7=Celik|first7=O.|last8=Cui|first8=W. |last9=Daniel|first9=M.|last10=d'Vali|first10=M.|last11=de la Calle Perez|first11=I.|display-authors=1|collaboration=VERITAS|year=2004|title=VERITAS: The Very Energetic Radiation Imaging Telescope Array System|journal=New Astronomy Reviews|volume=48|issue=5–6|pages=637–641|arxiv=astro-ph/9907248|bibcode=2004NewAR..48..345K|doi=10.1016/j.newar.2003.12.050|first13=A.|first27=J.|first24=T. A.|last25=Hanna|first25=D.|last26=Hillas|first26=A. M.|last27=Holder|last28=Horan|first23=J.|first28=D.|last29=Jarvis|first29=A.|last30=Jordan|first30=M.|first12=C.|last12=Duke|last24=Hall|last23=Hall|last14=Fegan|last18=Gaidos|first14=D. J.|last13=Falcone |first15=S. J.|last16=Finley|first16=J. P.|last17=Fortson|first17=L. F.|author17-link=Lucy Fortson|first18=J.|first22=J.|last19=Gammell|first19=S.|last20=Gibbs|first20=K.|last21=Gillanders|first21=G. H. |last22=Grube|last15=Fegan}}</ref> The reflector consists of 350 individual mirror facets, hexagonal in shape, mounted on a rigid optical support structure. The camera on each telescope has 499 individual pixels (high-speed 26 mm-diameter [[photomultiplier tubes]]). VERITAS, like other [[IACT]]s, is sensitive to primary particles that produce sufficient atmospheric Cherenkov light to be detectable at the ground. Its full range of sensitivity is from 50 GeV to 50 TeV (although the spectral reconstruction does not start until at least 100 GeV, depending on source strength). The energy and angular resolution depend on the energy of the incident gamma ray but at 1 TeV the energy resolution is ~17%, and the angular resolution is 0.08 degrees (65% containment radius). The entire array has a peak effective area of 100,000 square meters above 1 TeV. A very weak astrophysical source with a gamma-ray flux only 1% of the [[Crab Nebula]] can be detected by VERITAS in under 25 hours of observation. Stronger sources can be detected in significantly less time.

[[Image:MMT FLWO Amado AZ 10359.jpg|thumb|upright=1.0|right|Mirrors on VERITAS telescope 3]]

In order to distinguish between the background events (i.e. [[particle shower|hadronic showers]] and [[muons]]) or noise (i.e. starlight and moonlight) and the targeted data (i.e. [[particle shower |electromagnetic showers]] produced by gamma rays), VERITAS uses a three-level trigger system. Level one corresponds to a level crossing on each pixel using [[constant fraction discriminator]]s. Level two is a pattern selection trigger, which selects photon-like showers, which have compact shapes, and eliminates most of the background showers, which produce more random shapes in each camera. Level three is the array trigger which looks for a coincidence in the arrival time of the shower at multiple telescopes.<ref name="Concept1">{{cite journal|doi=10.1016/S0927-6505(01)00152-9|title=VERITAS: The Very Energetic Radiation Imaging Telescope Array System|journal=Astroparticle Physics|volume=17|issue=2|pages=221–243|year=2002|last1=Weekes|first1=T. C.|last2=Badran|first2=H.|last3=Biller|first3=S. D.|last4=Bond|first4=I.|last5=Bradbury|first5=S.|last6=Buckley|first6=J.|last7=Carter-Lewis|first7=D.|last8=Catanese|first8=M.|last9=Criswell|first9=S.|last10=Cui|first10=W.|last11=Dowkontt|first11=P.|last12=Duke|first12=C. |last13=Fegan|first13=D. J.|last14=Finley|first14=J.|last15=Fortson|first15=L.|author15-link=Lucy Fortson|last16=Gaidos|first16=J.|last17=Gillanders|first17=G. H.|last18=Grindlay|first18=J.|last19=Hall|first19=T. A.|last20=Harris|first20=K.|last21=Hillas|first21=A. M.|last22=Kaaret|first22=P.|last23=Kertzman|first23=M.|last24=Kieda|first24=D.|last25=Krennrich|first25=F.|last26=Lang|first26=M. J. |last27=Lebohec|first27=S.|last28=Lessard|first28=R.|last29=Lloyd-Evans|first29=J.|last30=Knapp|first30=J.|display-authors=1|collaboration=VERITAS|arxiv=astro-ph/0108478|bibcode=2002APh....17..221W|s2cid=119408725 }}</ref>

The [[Cherenkov radiation|Cherenkov light]] that is produced by gamma rays in the upper atmosphere is very dim, so VERITAS observes best under clear, dark skies. Observations are not possible under cloudy or rainy skies, or when the Moon is very bright. However, observations are regularly made when the Moon is dim or moderate in brightness (typically less than 60% illumination). The total yearly observation time is typically around 1,200 hours (of which around 200–250 hours is during brighter moonlight with illumination between 20 and 60%). The observatory does not generally collect data in July or August due to local monsoon conditions.

== History ==
VERITAS was designed to explore the very high energy (VHE) gamma-ray sky above 100 [[GeV]], following up on the success of the Whipple 10 m gamma-ray telescope. The Whipple telescope pioneered the use of an imaging Cherenkov camera, coupled with a large 10 m diameter reflector, to make the first definitive detection of a VHE gamma-ray source, the [[Crab Nebula]] in 1989.<ref>{{cite journal|last1=Weekes|first1=T. C.|last2=Cawley|first2=M. F.|last3=Fegan|first3=D. J.|last4=Gibbs|first4=K. G.|last5=Hillas|first5=A. M.|last6=Kowk|first6=P. W.|last7=Lamb|first7=R. C.|last8=Lewis|first8=D. A.|last9=Macomb|first9=D. |last10=Porter|first10=N. A.|last11=Reynolds|first11=P. T.|date=1989|title=Observation of TeV Gamma Rays from the Crab Nebula Using the Atmospheric Cerenkov Imaging Technique|journal=The Astrophysical Journal |volume=342|page=379|doi=10.1086/167599|bibcode=1989ApJ...342..379W|s2cid=119424766 |issn=0004-637X|url=http://mural.maynoothuniversity.ie/12618/1/Cawley_ObservationTeV_1989.pdf}}</ref> Subsequently, the [[HEGRA]] telescope on La Palma demonstrated good sensitivity above 1 TeV using an array of imaging atmospheric Cherenkov telescopes. VERITAS combines the benefits of stereoscopic observations in an array with large reflectors for a low energy threshold. Compared to the Whipple telescope, VERITAS employs larger 12 m diameter reflectors, improved optics and light collection efficiency, and a finer pixelated camera. Both the recording (using 500 MS/s custom-made Flash-ADCs) and trigger electronics (using a sophisticated three-level system) were significantly improved compared to earlier instruments. VERITAS was conceived in the 1990s, along with three other imaging atmospheric Cherenkov telescope (IACT) arrays: CANGAROO-III, [[High Energy Stereoscopic System|H.E.S.S.]] and [[MAGIC (telescope)|MAGIC]]. VERITAS is currently the only IACT array operating in the western hemisphere.

The first proposal for VERITAS (called VHEGRA at the time) was submitted by [[Trevor C. Weekes|Trevor Weekes]] ([[Smithsonian Astrophysical Observatory]] (SAO)) to the Smithsonian Institution in 1995; this proposal described an array of nine 10 m diameter Cherenkov telescopes. In 1998, the first VERITAS collaboration meeting was held at the [[University of Chicago]]. In 2000, the concept of VERITAS as a seven telescope array was recommended by the 2000 Decadal Survey in Astronomy and Astrophysics as a moderate-sized project.<ref>{{cite book|last=Council|first=National Research|url=https://www.nap.edu/catalog/9839/astronomy-and-astrophysics-in-the-new-millennium|title=Astronomy and Astrophysics in the New Millennium|date=2000-05-18|publisher=National Academies Press |isbn=978-0-309-07031-7}}</ref> Delays were incurred due to difficulties with two proposed sites in Arizona (Montosa Canyon at the base of [[Mount Hopkins (Arizona)|Mount Hopkins]] and [[Kitt Peak]]) and due to a reduction in available funding. The proposal for a four telescope array (now with 12 m diameter reflectors) was favorably reviewed in 2002 and construction of VERITAS started in 2003 at the [[Fred Lawrence Whipple Observatory]]. An initial prototype telescope was completed as Telescope #1 and saw first light in 2004. The construction of Telescope #2 was completed in 2005 and first stereo observations started that year. Telescopes #3 and #4 were completed by early 2007 and the first light celebration for the full for telescope array was on 27-28 April 2007.<ref name="VERITAS Home">{{cite web|title=VERITAS Homepage|url=http://veritas.sao.arizona.edu|access-date=13 April 2015|publisher=Smithsonian Astrophysical Observatory}}</ref> Regular science operations for VERITAS started in September 2007. The construction of VERITAS was largely funded in the U.S. by [[United States Department of Energy|Department of Energy]], the [[National Science Foundation]], and the [[Smithsonian Institution]]. Additional construction funding was provided by Enterprise Ireland (now [[Science Foundation Ireland]]) and the [[Particle Physics and Astronomy Research Council]] in the [[United Kingdom]].

Improvements and upgrades to VERITAS have been made periodically since 2007. Telescope #1 was moved in the summer of 2009 to a new location for better array geometry (and improved gamma-ray sensitivity).<ref name="Relocation"/> Between 2009 and 2011 an upgrade program was carried out that improved the alignment of the VERITAS mirror facets and replaced the level 2 trigger system. Furthermore, in the summer of 2012 all of the camera photomultiplier tubes were upgraded to high-quantum-efficiency tubes, which again increased the sensitivity, especially near the low end of the gamma-ray energy range. Compared to its initial design sensitivity, the actual achieved sensitivity of VERITAS is significantly better with the time required to detect weak gamma-ray sources reduced by more than a factor of two.<ref name="VERITAS Home"/>

In June 2017, a celebration was held at the Whipple Observatory to celebrate ten years of VERITAS science.<ref>{{cite web|title=VERITAS 10 Year Celebration|url=http://veritasj.sao.arizona.edu/10Years/|access-date=2020-08-01|website=veritasj.sao.arizona.edu}}</ref>

== Science ==
VERITAS has a broad science program that combines key aspects of astronomy, exploring the universe in the new waveband of VHE gamma rays, and physics, searching for new particles of phenomena beyond the [[Standard Model|standard model]] of particle physics. The basic questions pursued include: understanding cosmic particle acceleration in our Galaxy (with special emphasis on understanding the origin of [[cosmic ray]]s) and beyond our Galaxy, probing extreme environments near compact objects such as [[neutron star]]s and [[black hole]]s, the nature of [[dark matter]] and the intergalactic magnetic field, and whether the [[speed of light]] is constant at these extreme gamma-ray energies. The VERITAS observational program includes Galactic sources such as [[supernova remnant]]s, [[pulsar]]s, [[pulsar wind nebula]]e, [[binary system]]s and the enigmatic gamma-ray source at the [[Galactic Center]]. Extragalactic sources include [[Active galactic nucleus|active galactic nuclei]], [[Starburst galaxy|starburst galaxies]], and [[gamma-ray burst]]s.  An important component of VERITAS observations is that associated with multi-wavelength and [[Multi-messenger astronomy|multi-messenger]] follow up, including [[fast radio burst]] (FRB), high energy [[neutrino]], and [[gravitational wave]] events. VERITAS has an extensive dark matter program, in which indirect searches are conducted to find VHE gamma rays resulting from the annihilation of dark matter particles. Most of these searches target the Galactic Center and [[dwarf spheroidal galaxies]]. Starting in 2017, the VERITAS science program was expanded to include observations in the optical waveband through high-time-resolution measurements of asteroid occultations and stellar intensity interferometry.

[[File:VERITAS sources 2019.png|thumb|upright=1.0|right|VERITAS Catalog of very high energy gamma-ray sources (as of January 2020)]]

As of 2020, VERITAS research had led to 58 [[Doctor of Philosophy|Ph.D.]]'s and more than 100 peer-reviewed publications. As shown in the figure, VERITAS has detected 63 astrophysical sources of very high energy gamma rays (as of January 2020). The first VERITAS source catalog had only six sources.

Some of the scientific highlights of VERITAS include: 
* 2008: discovery of the first blazar of the intermediate frequency peaked [[BL Lacertae object|BL Lacertae]] (IBL) type at very high energies, W Comae<ref>{{Cite web|title=ATel #1422: VERITAS discovers TeV gamma rays from W Comae|url=http://www.astronomerstelegram.org/?read=1422|access-date=2020-08-01|website=ATel}}</ref> followed by a second IBL 3C 66A.<ref>{{Cite web|title=ATel #1753: Discovery of >100 GeV Gamma-ray Emission from the Blazar 3C66A by VERITAS|url=http://www.astronomerstelegram.org/?read=1753|access-date=2020-08-01|website=ATel}}</ref>

* 2009: discovery of the first starburst galaxy to emit at gamma-ray energies, the Cigar Galaxy or [[Messier 82|M 82.]]<ref>{{cite arXiv|last1=Ong|first1=R. A.|last2=Acciari|first2=V. A.|last3=Arlen|first3=T. |last4=Aune|first4=T.|last5=Beilicke|first5=M.|last6=Benbow|first6=W.|last7=Boltuch|first7=D.|last8=Bradbury|first8=S. M.|last9=Buckley|first9=J. H.|last10=Bugaev|first10=V.|last11=Byrum|first11=K.|date=2009-12-29|title=Highlight Talk: Recent Results from VERITAS|class=astro-ph.HE|eprint=0912.5355}}</ref><ref>{{Cite journal|last1=Acciari|first1=V. A.|last2=Aliu|first2=E.|last3=Arlen|first3=T.|last4=Aune|first4=T. |last5=Bautista|first5=M.|last6=Beilicke|first6=M.|last7=Benbow|first7=W.|last8=Boltuch|first8=D.|last9=Bradbury|first9=S. M.|last10=Buckley|first10=J. H.|last11=Bugaev|first11=V.|date=2009|title=A connection between star formation activity and cosmic rays in the starburst galaxy M82|url=https://www.nature.com/articles/nature08557|journal=Nature|volume=462|issue=7274|pages=770–772|doi=10.1038/nature08557 |pmid=19881491|arxiv=0911.0873|bibcode=2009Natur.462..770V|hdl=10379/1705|s2cid=205218873|issn=1476-4687}}</ref> This result was significant because it represented the first extragalactic object detected where the gamma rays are thought to be produced through typical astrophysical processes found in our Galaxy, as opposed to extreme processes found in the jets of [[Active galactic nucleus|active galactic nuclei]].<ref>{{cite web|date=November 2, 2009|title=VERITAS telescope array helps solve the origin of cosmic rays|url=https://astronomy.com/news/2009/11/veritas-telescope-array-helps-solve-the-origin-of-cosmic-rays|access-date=2020-08-01|website=Astronomy.com}}</ref>

* 2010; detection of extended gamma-ray emission from the [[IC 443|Jellyfish Nebula]] or IC 443,<ref>{{cite journal|last1=V. A. Acciari|last2=E. Aliu|last3=T. Arlen|last4=T. Aune|last5=M. Bautista|last6=M. Beilicke|last7=W. Benbow|last8=S. M. Bradbury|last9=J. H. Buckley|last10=V. Bugaev|last11=Y. Butt|title=Observation of Extended Very High Energy Emission from the Supernova Remnant Ic 443 with Veritas|date=2009-06-01|url=https://iopscience.iop.org/article/10.1088/0004-637X/698/2/L133/meta|journal=The Astrophysical Journal Letters|language=en|volume=698|issue=2|pages=L133–L137|doi=10.1088/0004-637X/698/2/L133|arxiv=0905.3291|bibcode=2009ApJ...698L.133A|s2cid=17001801|issn=1538-4357}}</ref> followed by detailed morphological studies by VERITAS which, when combined with data from [[Fermi Gamma-ray Space Telescope|Fermi-LAT]], provide strong evidence for the acceleration of cosmic rays by a Galactic supernova remnant.<ref>{{Cite journal|last1=Hewitt|first1=John W.|last2=Hays|first2=Elizabeth A.|author2-link=Elizabeth Hays|last3=Tajima|first3=Hiro|last4=Schmid|first4=Julia|last5=LAT Collaboration|first5=VERITAS Collaboration|date=2016|title=Resolving the hadronic accelerator IC 443 with Fermi-LAT and VERITAS|journal=American Astronomical Society Meeting Abstracts #227|language=en|volume=227|pages=238.10|bibcode=2016AAS...22723810H}}</ref>

* 2011: discovery of a new and unexpected component of gamma-ray emission above 100 GeV from the [[Crab Pulsar]], seriously challenging existing pulsar models.<ref>{{Cite journal|last1=Collaboration|first1=The VERITAS|last2=Aliu|first2=E.|last3=Arlen|first3=T.|last4=Aune|first4=T.|last5=Beilicke|first5=M.|last6=Benbow|first6=W.|last7=Bouvier|first7=A.|last8=Bradbury|first8=S. M.|last9=Buckley|first9=J. H.|last10=Bugaev|first10=V.|last11=Byrum|first11=K.|date=2011-10-07|title=Detection of Pulsed Gamma Rays Above 100 GeV from the Crab Pulsar|url=https://www.science.org/doi/10.1126/science.1208192|journal=Science|language=en|volume=334|issue=6052|pages=69–72|doi=10.1126/science.1208192|issn=0036-8075|pmid=21980105|arxiv=1108.3797|bibcode=2011Sci...334...69V|hdl=10379/10213 |s2cid=5767438}}</ref>

* 2011: discovery of TeV gamma-ray emission from the [[SN 1572|Tycho supernova remnant]],;<ref>{{Cite journal|last1=Acciari|first1=V. A.|last2=Aliu|first2=E.|last3=Arlen|first3=T.|last4=Aune|first4=T.|last5=Beilicke|first5=M.|last6=Benbow|first6=W.|last7=Bradbury|first7=S. M.|last8=Buckley|first8=J. H.|last9=Bugaev|first9=V.|last10=Byrum|first10=K.|last11=Cannon|first11=A.|date=2011-04-01|title=Discovery of TeV Gamma Ray Emission from Tycho's Supernova Remnant|arxiv=1102.3871|journal=The Astrophysical Journal|volume=730|issue=2|pages=L20|doi=10.1088/2041-8205/730/2/L20|bibcode=2011ApJ...730L..20A|s2cid=37710923|issn=2041-8205}}</ref> this remnant resulted from one of the few historical supernovae in our Galaxy.

* 2013: locating the gamma-ray emission in the jet of an [[active galactic nucleus]], through the combination of VHE gamma-ray observations made by VERITAS and high angular resolution observations made by the [[Very Long Baseline Array]].<ref>{{Cite journal|last1=Arlen|first1=T.|last2=Aune|first2=T.|last3=Beilicke|first3=M.|last4=Benbow|first4=W.|last5=Bouvier|first5=A.|last6=Buckley|first6=J. H.|last7=Bugaev|first7=V.|last8=Cesarini|first8=A.|last9=Ciupik|first9=L.|last10=Connolly|first10=M. P.|last11=Cui|first11=W.|date=2013|title=Rapid TeV Gamma-Ray Flaring of BL Lacertae|journal=The Astrophysical Journal|language=en|volume=762|issue=2|pages=92|doi=10.1088/0004-637X/762/2/92|arxiv=1211.3073|bibcode=2013ApJ...762...92A|s2cid=73682728|issn=0004-637X}}</ref>

* 2015: detection of TeV gamma rays from the quasar PKS 1441+25 at a [[redshift]] value ~ 1, indicating the general transparency of the universe to photons at these energies.<ref>{{Cite journal|last1=Abeysekara|first1=A. U.|last2=Archambault|first2=S.|last3=Archer|first3=A.|last4=Aune|first4=T.|last5=Barnacka|first5=A.|author-link5=Anna Barnacka|last6=Benbow|first6=W.|last7=Bird|first7=R.|last8=Biteau|first8=J.|last9=Buckley|first9=J. H.|last10=Bugaev|first10=V.|last11=Cardenzana|first11=J. V.|date=2015-12-15|title=Gamma rays from the quasar PKS 1441+25: story of an escape|arxiv=1512.04434|journal=The Astrophysical Journal|volume=815|issue=2|pages=L22|doi=10.1088/2041-8205/815/2/L22|bibcode=2015ApJ...815L..22A|s2cid=14656914|issn=2041-8213}}</ref>

* 2018: detection of VHE gamma rays from direction of the [[BL Lacertae object|BL Lac object]] [[TXS 0506+056]],<ref>{{Cite journal|last1=Abeysekara|first1=A. U.|last2=Archer|first2=A.|last3=Benbow|first3=W.|last4=Bird|first4=R.|last5=Brill|first5=A.|last6=Brose|first6=R.|last7=Buckley|first7=J. H.|last8=Christiansen|first8=J. L.|last9=Chromey|first9=A. J.|last10=Daniel|first10=M. K.|last11=Falcone|first11=A.|date=2018-07-12|title=VERITAS Observations of the BL Lac Object TXS 0506+056|journal=The Astrophysical Journal|language=en|volume=861|issue=2|pages=L20|doi=10.3847/2041-8213/aad053|arxiv=1807.04607|bibcode=2018ApJ...861L..20A|s2cid=119228278|issn=2041-8213 |doi-access=free }}</ref> that is coincident with the high-energy neutrino event IC 170922A reported by the [[IceCube Neutrino Observatory|IceCube]] neutrino telescope.
* 2019-2020: direct measurement of stellar angular diameters by an imaging atmospheric Cherenkov telescope<ref>{{Cite journal|last1=Benbow|first1=W.|last2=Bird|first2=R.|last3=Brill|first3=A.|last4=Brose|first4=R.|last5=Chromey|first5=A. J.|last6=Daniel|first6=M. K.|last7=Feng|first7=Q.|last8=Finley|first8=J. P.|last9=Fortson|first9=L.|author9-link= Lucy Fortson |last10=Furniss|first10=A.|last11=Gillanders|first11=G. H.|date=2019|title=Direct measurement of stellar angular diameters by the VERITAS Cherenkov telescopes|journal=Nature Astronomy|language=en|volume=3|issue=6|pages=511–516|doi=10.1038/s41550-019-0741-z|arxiv=1904.06324|bibcode=2019NatAs...3..511B|s2cid=118637418|issn=2397-3366}}</ref> and demonstration of stellar intensity interferometry with a modern telescope system.<ref>{{Cite journal|last1=Abeysekara|first1=A. U.|last2=Benbow|first2=W.|last3=Brill|first3=A.|last4=Buckley|first4=J. H.|last5=Christiansen|first5=J. L.|last6=Chromey|first6=A. J.|last7=Daniel|first7=M. K.|last8=Davis|first8=J.|last9=Falcone|first9=A.|last10=Feng|first10=Q.|last11=Finley|first11=J. P.|date=2020|title=Demonstration of stellar intensity interferometry with the four VERITAS telescopes|journal=Nature Astronomy|volume=4|issue=12|pages=1164–1169|language=en|doi=10.1038/s41550-020-1143-y|arxiv=2007.10295|bibcode=2020NatAs...4.1164A|s2cid=220646525|issn=2397-3366}}</ref>

VERITAS researchers have also pioneered the use of an [[IACT]] to carry out [[Citizen science|Citizen Science]]. To improve the detection of [[muon]] events, the Muon Hunter project was created on the [[Zooniverse]] platform. The project showed images taken with VERITAS and citizen volunteers had to classify the images as muon or non-muon events. The researchers then trained a [[Machine learning|machine learned]] algorithm that performed better than the standard analysis.<ref>{{Cite arXiv|last1=Bird|first1=R.|last2=Daniel|first2=M. K.|last3=Dickinson|first3=H.|last4=Feng|first4=Q.|last5=Fortson|first5=L.|author5-link= Lucy Fortson |last6=Furniss|first6=A.|last7=Jarvis|first7=J.|last8=Mukherjee|first8=R.|last9=Ong|first9=R.|last10=Sadeh|first10=I.|last11=Williams|first11=D.|date=2018-02-24|title=Muon Hunter: a Zooniverse project|eprint=1802.08907|class=astro-ph.IM}}</ref> In Muon Hunter 2.0 the project will try to improve the result with a different machine learning approach.<ref>{{Cite web|url=https://www.zooniverse.org/projects/dwright04/muon-hunters-2-dot-0/about/research|title=Muon Hunters 2.0 About - Zooniverse|website=www.zooniverse.org|access-date=2019-12-19}}</ref>

==Collaboration==
The VERITAS collaboration was officially formed by the signing of a teaming agreement in 2000 between nine member institutions in three countries. The member institutions were: [[Iowa State University]], [[Purdue University]], [[Smithsonian Astrophysical Observatory]], [[University of California, Los Angeles]], [[University of Chicago]], [[University of Utah]], and [[Washington University in St. Louis]] in the U.S., [[University of Leeds]] in the U.K. and [[National University of Ireland, Dublin|National University of Ireland Dublin]] in Ireland.  A tenth member institution, [[McGill University]] in Canada, was added with an updated agreement in 2008.  Representatives from the member institutions form the VERITAS Executive Council (VEC), that serves as the ultimate decision-making authority within the collaboration.<ref name="VERITAS Home" />

In 2008, the collaboration was enlarged by the addition of collaborating institutions that have representation on the VERITAS Science Board, that directs the science program of VERITAS.  The initial collaborating institutions were: [[Adler Planetarium]], [[Barnard College]], [[Cork Institute of Technology]], [[DePauw University]], [[Galway-Mayo Institute of Technology]], [[Grinnell College]], [[NUI Galway|National University of Ireland, Galway]], [[University of California, Santa Cruz]], [[University of Iowa]] and [[University of Massachusetts Amherst|University of Massachusetts, Amherst]].

As of 2019, the VERITAS collaboration consists of ~80 scientists from institutions in Canada, Germany, Ireland and the U.S.  The participating institutions are: [[Barnard College]], [[Columbia University]], [[Cork Institute of Technology]], [[DESY]], [[Georgia Tech|Georgia Institute of Technology]], [[Iowa State University]], [[McGill University]], [[NUI Galway|National University of Ireland, Galway]], [[Purdue University]], [[Smithsonian Astrophysical Observatory]], [[University College Dublin]], [[University of California, Los Angeles]], [[University of California, Santa Cruz]], [[University of Chicago]], [[University of Delaware]], [[University of Iowa]], [[University of Minnesota]], [[University of Utah]], and [[Washington University in St. Louis]]. There are also non-affiliated and associate members from a number of other institutions.<ref name="VERITAS Home" />

The chair of the VERITAS Science Board is the Spokesperson.  There is a Deputy Spokesperson to assist in the leadership of the collaboration. A chronological list of the VERITAS Spokespersons and Deputy Spokespersons is given in the table below.  Starting in 2007, the Spokesperson/Deputy Spokesperson served a two-year term and may be re-elected.
{| class="wikitable"
|+
!Dates
!Spokesperson
!Deputy Spokesperson
|-
|2000-2007
|Trevor Weekes (SAO)
|n/a
|-
|2007-2009
|[[Simon Swordy]] (U. Chicago)
|[[Rene Ong]] (UCLA)
|-
|2009-2011
|[[Rene Ong]] (UCLA)
|Jamie Holder (U. Delaware)
|-
|2011-2013
|[[Rene Ong]] (UCLA)
|[[Reshmi Mukherjee]] (Barnard College)
|-
|2013-2015
|Jamie Holder (U. Delaware)
|John Finley (Purdue U.)
|-
|2015-2017
|[[Reshmi Mukherjee]] (Barnard College)
|Scott Wakely (U. Chicago)
|-
|2017-2019
|[[Reshmi Mukherjee]] (Barnard College)
|Scott Wakely (U. Chicago)
|-
|2019-2021
|John Quinn (UCD)
|David Williams (UCSC)
|-
|2021-2023
|John Quinn (UCD)
|Amy Furniss (CSU, East Bay)
|-
|2023-2025
|Amy Furniss (CSU, East Bay)
|Manel Errando (Washington Univ.)
|}

As of 2019, the following agencies provide operational funding for VERITAS: the [[National Science Foundation]] and the [[Smithsonian Institution]] in the U.S., the [[Natural Sciences and Engineering Research Council]] in Canada, the [[Helmholtz Association of German Research Centres|Helmholtz Association]] in Germany.

==See also==
*[[Fermi Gamma-ray Space Telescope]]
*[[High Energy Stereoscopic System]]
*[[IACT]]
*[[List of astronomical observatories]]
*[[MAGIC (telescope)]]

==References==
{{Reflist}}

==External links==
{{Commons category|VERITAS}}
*[http://veritas.sao.arizona.edu Official VERITAS Site]

{{Portal bar|Arizona|Astronomy|Stars|Spaceflight|Outer space|Solar System|Education|Science}}
{{DEFAULTSORT:Veritas}}
[[Category:Gamma-ray telescopes]]
[[Category:Cosmic-ray telescopes]]
[[Category:Astronomical observatories in Arizona]]
[[Category:Buildings and structures in Santa Cruz County, Arizona]]
[[Category:Fred Lawrence Whipple Observatory]]
[[Category:Articles containing video clips]]