Kenneth J. Ragan, McGill University
Physics
Professor
Montreal, Quebec
ken.ragan@mcgill.ca
Office:
(514) 398-6518
Bio/Research
My major research interests are centred on my work at the Fred Lawrence Whipple Observatory of the SAO (Smithsonian Astrophysical Observatory), where I'm involved with the VERITAS collaboration. Formerly, my major effort was in Albuquerque, New Mexico, on the STACEE collaboration.
Both S...
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Both S...
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Bio/Research
My major research interests are centred on my work at the Fred Lawrence Whipple Observatory of the SAO (Smithsonian Astrophysical Observatory), where I'm involved with the VERITAS collaboration. Formerly, my major effort was in Albuquerque, New Mexico, on the STACEE collaboration.
Both STACEE and VERITAS are air Cherenkov instruments, in which high energy gamma-rays impinging on the upper atmosphere create showers of charged secondary particles. These secondaries are energetic enough to be moving faster than the (local!) speed of light in the upper atmosphere and so they in turn emit Cherenkov light. Cherenkov light is the bluish emission that is the electromagnetic equivalent of a sonic boom from a supersonic aircraft. It is probably familar to you from the bluish glow visible in photographs of stored spent nuclear fuel rods, where the emitted radiation (electrons) emit the Cherenkov light in water.
In STACEE and VERITAS we detect the Cherenkov light at ground level even though, by that point, the shower of secondary particles has been absorbed high up in the atmosphere. Measuring the properties of the Cherenkov light (intensity and direction) allows us to infer the direction and energy of the original high energy gamma-ray, and thus to do gamma-ray astronomy.
STACEE was operated from 1996 to 2007 and that used the wavefront-sampling technique to observe astrophysical sources of high energy gamma-rays. In particular, the gamma-ray energy range between about 40 GeV and 200 GeV is an energy regime which is largely unexplored to date, and STACEE's goal was to be sensitive to part of this range. Both lower energy (space-based) and higher energy (ground-based) detectors have observed numerous sources, primarily Active Galactic Nuclei (AGNs) and Supernova Remnants (SNRs), and this energy regime is thought to be a crucial part of the effort to understand the mechanisms powering these sources.
VERITAS' goals are similar, although the technique is quite different; while STACEE was a wavefront sampling detector, VERITAS is an array of four multiple imaging telescopes, each 12 m in size. Individual imaging telescopes in the gamma-ray regime have operated very successfully for many years above an energy of about 250 GeV. With multiple imaging telescopes, the sensitivity of the technique increases (allowing us to see weaker gamma-ray sources) and the threshold energy decreases (again allowing us to explore the 50 GeV to few-hundred GeV regime). VERITAS is currently the world's most sensitive air Cherenkov instrument.
The McGill gamma-ray astrophysics research group currently consists of two faculty (Prof. David Hanna and myself), two post-doctoral researchers and five graduate students.
I have other interests in the more traditional field of accelerator-based particle physics, in non-accelerator (underground) particle physics and particle astrophysics, and in detector technology.
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Both STACEE and VERITAS are air Cherenkov instruments, in which high energy gamma-rays impinging on the upper atmosphere create showers of charged secondary particles. These secondaries are energetic enough to be moving faster than the (local!) speed of light in the upper atmosphere and so they in turn emit Cherenkov light. Cherenkov light is the bluish emission that is the electromagnetic equivalent of a sonic boom from a supersonic aircraft. It is probably familar to you from the bluish glow visible in photographs of stored spent nuclear fuel rods, where the emitted radiation (electrons) emit the Cherenkov light in water.
In STACEE and VERITAS we detect the Cherenkov light at ground level even though, by that point, the shower of secondary particles has been absorbed high up in the atmosphere. Measuring the properties of the Cherenkov light (intensity and direction) allows us to infer the direction and energy of the original high energy gamma-ray, and thus to do gamma-ray astronomy.
STACEE was operated from 1996 to 2007 and that used the wavefront-sampling technique to observe astrophysical sources of high energy gamma-rays. In particular, the gamma-ray energy range between about 40 GeV and 200 GeV is an energy regime which is largely unexplored to date, and STACEE's goal was to be sensitive to part of this range. Both lower energy (space-based) and higher energy (ground-based) detectors have observed numerous sources, primarily Active Galactic Nuclei (AGNs) and Supernova Remnants (SNRs), and this energy regime is thought to be a crucial part of the effort to understand the mechanisms powering these sources.
VERITAS' goals are similar, although the technique is quite different; while STACEE was a wavefront sampling detector, VERITAS is an array of four multiple imaging telescopes, each 12 m in size. Individual imaging telescopes in the gamma-ray regime have operated very successfully for many years above an energy of about 250 GeV. With multiple imaging telescopes, the sensitivity of the technique increases (allowing us to see weaker gamma-ray sources) and the threshold energy decreases (again allowing us to explore the 50 GeV to few-hundred GeV regime). VERITAS is currently the world's most sensitive air Cherenkov instrument.
The McGill gamma-ray astrophysics research group currently consists of two faculty (Prof. David Hanna and myself), two post-doctoral researchers and five graduate students.
I have other interests in the more traditional field of accelerator-based particle physics, in non-accelerator (underground) particle physics and particle astrophysics, and in detector technology.
Click to Shrink <<