VERITAS (Very Energetic Radiation Imaging
Telescope Array System) is
a major ground-based gamma-ray observatory with an array of four 12
meter optical reflectors for gamma-ray astronomy in the GeV – TeV
photon energy range.
VERITAS uses the Imaging Atmospheric Cherenkov
Telescope technique to observe gamma-rays that cause particle showers
in Earth's upper atmosphere. The telescope design is based on the
design of the existing 10m gamma-ray telescope at the Fred Lawrence
Observatory . It consists of an array of imaging telescopes
deployed such that they permit the maximum versatility and give the
highest sensitivity in the 50 GeV – 50 TeV band (with sensitivity
from 100 GeV to over 10 TeV). This very high energy observatory,
completed in 2007, effectively complements Fermi Gamma-ray Space
Telescope due to its large collection area as well as its higher
* 1 Specifications and design
* 2 History
* 3 Science
* 4 Collaboration
* 4.1 Member institutions
* 4.2 Collaborators
* 5 See also
* 6 References
* 7 External links
SPECIFICATIONS AND DESIGN
VERITAS is constructed of four 12 m Imaging Atmospheric Cherenkov
Telescopes with an approximate separation of 100 meters (330 feet)
from each adjacent telescope. The four telescope array is needed for
stereoscopic observations. These stereoscopic observations allow the
reconstruction of the particle shower geometry, thus giving precise
angular and energy resolution. The angular resolution is acquired by
finding the center axis of the spread of the shower on each telescope
and tracing those lines until they cross. The intersection of these
lines is the direction of the source of the gamma ray. This is
depicted on the figure to the right. Each telescope sees the particle
shower at a specific region in its camera (shown as grey ellipses),
and thus the source of the shower can be found.
Each of the individual telescopes have a 39 feet aperture, 350
mirrors on each dish, 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 easy to construct and align. This design does cause a
small time spread in the signal, but this spread is very small (~ 4
nanoseconds). The camera on each telescope has 499 individual
photomultiplier tubes . VERITAS, like other IACTs , are most sensitive
to the highest energy cosmic rays. Its full range of sensitivity is
from 85 GeV to over 30 TeV (although the spectral reconstruction does
not start until at least 100 GeV). 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. The
entire array has an effective area of 100,000 square meters.
VERITAS telescope 3
In order to distinguish between the background noise (e.g. hadronic
showers , starlight, moonlight, and muons )) and the targeted data
(i.e. electromagnetic showers produced from gamma rays),
a three-level trigger system. Level one corresponds to the
discriminators on each pixel using constant fraction discriminators .
Level two is a pattern selection trigger, which selects only
photon-initiated showers, which have compact shapes, and background
pulses, which have more random distributions. Level three is the array
trigger which looks for coincidence between multiple telescopes.
The Cherenkov light that is produced by cosmic rays in the upper
atmosphere is very dim, so
VERITAS can only observe under clear, dark
skies. Observations are not possible under cloudy or rainy skies, or
when the moon is bright. This shrinks the observation time to
approximately 70–100 hours each month from September until June. The
observatory does not collect data in July or August due to local
The Very Energetic Radiation Imaging
Telescope Array System was built
as first next generation
IACT in the western hemisphere. It was
originally planned as an array of seven telescopes, but only four were
constructed in the end. Each telescope was based on the design of the
Wipple 10 m telescope that is also present at the Fred Lawrence
Observatory but with significant updates to the reflector
optics, light collection efficiency, signal chain, and recording
electronics. This was perceived as a significant step up from the
previous generation of instruments such as Whipple,
HEGRA , and
Cherenkov Array at Themis . The original
VERITAS prototype telescope
was installed in April 2003 and saw first light in February 2004.
Positions of the
VERITAS telescopes before and after the relocation.
After, the success of the first telescope, construction was completed
on the other three telescopes in January 2007, and the first light
celebration for the full 4 telescope array was on April 27–28, 2007.
More recently, telescope number #1 was moved to a new location for
improved sensitivity in the summer of 2009. For historical reasons,
telescopes number #1 and #4 were built only 35 meters (115 ft) apart,
which almost made them redundant in the array. After the move, the
sensitivity of the array was increased by 30% corresponding to a 60%
decrease in time to detect a source. Furthermore, in the summer of
2012 all of the camera photomultipliers were upgraded to
high-quantum-efficiency photomultipliers, which again increased the
sensitivity especially near the low end of the energy range.
VERITAS cosmic ray observations further the study of astrophysical
objects that emit high-energy cosmic rays, such as:
* Active Galactic Nuclei
* Gamma-ray Bursts
* Unidentified sources of cosmic rays
The study of these objects has been going on since 2008, and there
have been a number important scientific highlights. In its first year
VERITAS detected two new sources with TeV energy, as
well as the detailed studies of two
Supernova remnants .
From 2007 to 2011,
VERITAS observed the Cab Pulsar and noted a
significant source above hundreds of GeVs , which was seen as
incompatible with the theoretical models of pulsars. All of the
galactic and extra-galactic sources that
VERITAS observes (as of
A large portion of the observation time ( ~400 h per year), has been
used to observe ~128 Active Galactic Nuclei and has identified many
blazars as well as performed deep studies of known sources.
VERITAS also has an extensive
Dark Matter program, in which indirect
searches are conducted to find very high energy gamma rays resulting
from the annihilation of
Dark Matter particles. Most of these searches
are conducted at the Galactic Center and in dwarf spheroidal galaxies
VERITAS is supported by the
United States Department of Energy , the
National Science Foundation , the
Smithsonian Institution , the
Natural Sciences and Engineering Research Council in Canada, Science
Foundation Ireland and the Particle Physics and Astronomy Research
Council in the U.K.
The collaboration is composed of several members and other
Iowa State University
Washington University in St. Louis
University of Chicago
University of Utah
University of Utah
University of California, Los Angeles
University College Dublin
University of Leeds
Argonne National Laboratory
Georgia Institute of Technology
University of California, Santa Cruz
University of California, Santa Cruz
University of Iowa
University of Iowa
University of Massachusetts Amherst
Cork Institute of Technology
Galway-Mayo Institute of Technology
National University of Ireland Galway
* Fermi Gamma-ray Space
High Energy Stereoscopic System
* ^ A B Perkins, Jeremy S.; Maier, Gernot; The VERITAS
Collaboration (2009). "
Telescope 1 Relocation: Details and
Improvements". arXiv :0912.3841 .
* ^ A B C Krennrich, F.; Bond, I. H.; Boyle, P. J.; Bradbury, S.
M.; Buckley, J. H.; Carter-Lewis, D.; Celik, O.; Cui, W.; Daniel, M.;
d'Vali, M.; de la Calle Perez, I.; Duke, C.; Falcone, A.; Fegan, D.
J.; Fegan, S. J.; Finley, J. P.; Fortson, L. F.; Gaidos, J.; Gammell,
S.; Gibbs, K.; Gillanders, G. H.; Grube, J.; Hall, J.; Hall, T. A.;
Hanna, D.; Hillas, A. M.; Holder, J.; Horan, D.; Jarvis, A.; et al.
(2004). "VERITAS: The Very Energetic Radiation Imaging
System". New Astronomy Reviews. 48 (5–6): 345. Bibcode
:2004NewAR..48..345K. doi :10.1016/j.newar.2003.12.050 .
* ^ Weekes, T. C.; Badran, H.; Biller, S. D.; Bond, I.; Bradbury,
S.; Buckley, J.; Carter-Lewis, D.; Catanese, M.; Criswell, S.; Cui,
W.; Dowkontt, P.; Duke, C.; Fegan, D. J.; Finley, J.; Fortson, L.;
Gaidos, J.; Gillanders, G. H.; Grindlay, J.; Hall, T. A.; Harris, K.;
Hillas, A. M.; Kaaret, P.; Kertzman, M.; Kieda, D.; Krennrich, F.;
Lang, M. J.; Lebohec, S.; Lessard, R.; Lloyd-Evans, J.; et al. (2002).
"VERITAS: The Very Energetic Radiation Imaging
System". Astroparticle Physics. 17 (2): 221. Bibcode
:2002APh....17..221W. arXiv :astro-ph/0108478 . doi
* ^ A B "
Smithsonian Astrophysical Observatory.
Retrieved 13 April 2015.
* ^ Kieda, David (2011). "Status of the
Proceedings of the 32nd International Cosmic Ray Conference
(ICRC2011). 9: 14.
Bibcode :2011ICRC....9...14K. arXiv :1110.4360 .
doi :10.7529/ICRC2011/V09/0343 .
* ^ Holder, J.; Acciari, V. A.; Aliu, E.; Arlen, T.; Beilicke, M.;
Benbow, W.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Butt, Y.;
Byrum, K. L.; Cannon, A.; Celik, O.; Cesarini, A.; Ciupik, L.; Chow,
Y. C. K.; Cogan, P.; Colin, P.; Cui, W.; Daniel, M. K.; Ergin, T.;
Falcone, A. D.; Fegan, S. J.; Finley, J. P.; Finnegan, G.; Fortin, P.;
Fortson, L. F.; Furniss, A.; Gillanders, G. H.; et al. (2008). "Status
VERITAS Observatory". AIP Conference Proceedings. p. 657. arXiv
:0810.0474 . doi :10.1063/1.3076760 .
* ^ A B C Galante, Nicola; for the
VERITAS Collaboration (2012).
"Status and Highlights of VERITAS". AIP Conference Proceedings: 202.
arXiv :1210.5480 . doi :10.1063/1.4772234 .