Cosmic explosions at the highest energies

The Cherenkov Telescope Array (https://www.cta-observatory.org) will be the world’s first observatory in the 30 GeV to 300 TeV band. It will have at least ten times the sensitivity of any previous instrument, and will also have much better spatial and spectral resolution. All previous instruments of this type have been consortia experiments, with no data access. Ground-based VHE gamma-ray telescopes work by detecting the nanosecond flash of blue Cherenkov light from the atmospheric particle shower that results from the impact of a VHE gamma-ray with an atom in the atmosphere. CTA will be the first air-shower system to make use of large numbers of telecopes, giving it its great scientific advantages. CTA will make its initial observations in 2018.

Gamma-ray bursts are the most energetic explosions in the Universe. Their physics is an area of intense research since they were discovered. The US/UK/Italian satellite Swift discovers a new GRB every few days, thanks to the Leicester-provided camera on its X-ray Telescope. Swift has transformed the study of GRBs due to its very high observational efficiency, leading to large numbers of distance measurements and to many new discoveries. Both long and short GRBs are thought to be due the creation of a new black hole, and they are respectively expected to be sources of neutrinos and gravitational waves.

The VHE emission of GRBs has not been seen so far, no air-shower telescope has been able to point at a burst quickly enough. CTA has a rapid slew capability designed in from the start, and offers great promise in this new frontier area. Although CTA is not expected to detect large numbers of GRBs, those that it does detect will be measured with high statistical quality. These first VHE measurements will be key to setting the future of the field. They will have the capability to constrain the nature of the inter-galactic medium between us and the burst, the physics and energetics of the bursts themselves, and possibly the nature of the hypothesized ‘spacetime foam’ by providing measurements of the speed of light at the highest energies.

The Department has a very active and successful transient astrophysics group, and is providing cameras for many of the CTA telescopes. We will have access to the early data from CTA, and we will need to be ready for it when it comes.