VERITAS has a long-term blazar monitoring program, shown here. In the table, clicking on the name will show the data taken to date.

A search function (for data taken on a specific date) is available here.

VERITAS Array
Artist's Impression of the VERITAS Array
To further work in high-energy gamma-ray astronomy, the Whipple group has proposed a next-generation telescope array which will be 10 times more sensitive than the existing Whipple telescope. In fact, the proposed new facility, called VERITAS (Very Energetic Radiation Imaging Telescope Array System), will be the most sensitive detector of its type in the world. The observations with VERITAS will be a key to understanding many physical processes in nature.

The array will consist of four 39-foot-aperture optical telescopes placed in a Mercedes pattern. Each large reflector will have a 499-pixel camera at its focus.

Since there is no other way to investigate these processes on Earth, the research done with VERITAS represents a rare use of "natural laboratories" in space to study the most powerful sources of electromagnetic energy known to science.

The construction of VERITAS has been endorsed by several national scientific panels and advisory groups. It will complement the next gamma-ray space telescope, GLAST, which is scheduled for launch by NASA in 2005.

VERITAS will be a truly national and international facility, promoting cooperation and collaboration with scores of scientific groups around the world. For example, the VERITAS collaboration will include not only members of the current Whipple Collaboration, but new groups from the University of Chicago, the University of Utah, the University of Chicago and McGill University in Montreal.

The construction of VERITAS is part of a continuing effort to provide U.S. astronomers with first-rate observing facilities so that they can maintain their leadership in astronomical scientific research and provide our students with first-rate training facilities. VERITAS will attract the attention of the world scientific community and will be an intellectual highlight of the Santa Cruz Valley.

The total cost of the VERITAS project is estimated to be $20.7 million. The annual operating and maintenance costs are estimated to be $1.5 million. Support for VERITAS is expected to be shared between the U.S. Department of Energy, the National Science Foundation, the Smithsonian Institution and funding agencies of the United Kingdom and Ireland.

 

Because it is very difficult to produce gamma-rays, the objects that emit them are very interesting to astrophysicists. High-energy gamma rays are associated with exploding stars (supernovae), pulsars , quasars , and black holes rather than with ordinary stars or galaxies.

The emission of high-energy gamma-rays from cosmic objects always implies the presence of exotic and extreme physical conditions - high magnetic and electric fields, shock waves, cataclysmic explosions, etc. In fact, this emission offers the only direct probe of the extreme conditions in these exciting phenomena.

Electromagnetic radiation that does not penetrate the Earth's atmosphere, like gamma-rays and X rays, is usually studied by telescopes carried above the atmosphere in satellites. As a result, these detectors are limited in size and very costly. Moreover, the flux of very high energy (VHE) gamma-rays (energies above ~ 100 GeV) is so small that even the largest space-based gamma-ray telescopes cannot see enough photons to detect the actual sources of this radiation.

Fortunately, some 50 years ago, physicists in the United Kingdom (UK) discovered that very-high-energy gamma-rays (and cosmic rays) can be detected from the ground via the secondary radiation they produce when they strike the atmosphere. The secondary radiation is produced as a brief flash of blue light named after the Russian physicist, Pavel Cherenkov. The light is extremely faint and can only be detected at a dark site under clear skies. Although this flash only lasts for a few billionths of a second, it can be detected with large optical light collectors equipped with photomultiplier tubes.

The study of cosmic gamma-rays is now a major part of astronomical research. Like all astronomy, this is basic research that probes the Universe for our greater understanding. It has no military objectives and no military support. All results from these studies are published in the international scientific literature and shared with colleagues at home and abroad. None of this work is classified.

10m at Sunset
The 10m Telescope at Sunset
The 10-meter (34-foot) optical reflector at the Whipple Observatory was built in 1968 to pursue studies in gamma-ray astronomy; it has been in almost continuous nightly use since that time. The technique developed at the Whipple Observatory is the most sensitive method of detecting very-high-energy gamma-rays. It is an important complement to the studies from space using the CGRO.

The first galactic source of very-high-energy gamma-rays, the Crab Nebula supernova remnant, was detected by the Whipple group in 1989. The first extragalactic source, the active galaxy Markarian 421, was detected by the same group in 1992. There are now more than one dozen known cosmic sources of very-high-energy gamma-rays.

The Whipple Gamma-Ray Collaboration includes the Smithsonian Astrophysical Observatory, Iowa State University, Purdue University, Washington University, Leeds University (UK), and the National University of Ireland. Major funding support has come from the U.S. Department of Energy. More than 20 students have completed their doctoral dissertations on work done at this facility since 1982.

Although there are now more than ten major gamma-ray observatories around the globe, the Whipple telescope is still the largest and most sensitive gamma-ray telescope. However, major new observatories that will surpass the sensitivity of the Whipple telescope are now under construction in Spain , Australia, and Namibia (Africa) by international collaborations.

 

Almost all of our information about the universe beyond our planet comes from the study of electromagnetic radiation. Gamma radiation is part of the electromagnetic spectrum that includes the familiar visible light and radio waves.

The Gamma Ray Sky
The Gamma Ray Sky ( Credit: EGRET Team, Compton Observatory, NASA)
All electromagnetic radiation travels as packets of energy call "photons". Gamma-ray photons have many properties similar to photons of visible light and radio waves: they travel in straight lines; they move at the speed of light; and they are not affected by magnetic or electric fields in space.

However, there are also many differences between gamma-rays and other forms of energy. For example, a gamma-ray photon has one million to one trillion (one million million) times the energy of a photon of visible light. And, unlike photons of radio and visible light, gamma-ray photons cannot penetrate the earth's atmosphere, for they are absorbed by interactions with air molecules ten miles above the Earth's surface. Also, gamma-rays cannot be reflected by mirrors. Thus, normal telescope optics cannot be used to enhance or increase the collection area of a gamma-ray detector.

Because gamma-rays can traverse great distances in space without absorption by intergalactic dust and gas, they can serve as powerful probes of distant regions of the cosmos as well as otherwise obscured regions of our own Milky Way.

Gamma-rays are produced on Earth from the radioactive decay of naturally occurring elements, and oncologists may use such gamma-rays to treat cancer tumors. Particle physicists can produce gamma-rays at accelerators such as Fermilab in Illinois or the Stanford Linear Accelerator in California, where they are used to study the properties of elementary matter. But very-high-energy gamma-rays like those emitted by astronomical bodies do not occur naturally on Earth.

  1. The Science of VERITAS