I’m a researcher working in gamma-ray astronomy, a branch of the wider field of high energy astrophysics. The theme underlying my research interests is the quest to understand the nature and origin of the energetic cosmic rays permeating our universe and continuously bombarding Earth.
Cosmic rays are charged particles, deflected by magnetic fields as they travel – consequently, their arrival direction often does not correspond to their origin. However, cosmic ray interactions at their source location produce neutral gamma rays that are not deflected; by studying these gamma rays, we can learn a lot about the origins of cosmic rays.
Gamma-ray Astronomy and High Energy Astrophysics
Gamma-ray astronomy uses the observation of gamma-rays to study natural energetic particle accelerators in our universe. What kinds of systems accelerate particles and how? What energies do they reach? Which particle types are accelerated where?
Imaging Atmospheric Cherenkov Telescopes (IACTs) observe very-high-energy (~1011-1014 eV) gamma-rays indirectly, by detecting Cherenkov radiation from extensive air showers – cascades of energetic particles initiated by a gamma-ray interaction in the atmosphere.
Images of gamma-ray extensive air showers are elliptical. The orientation provides information about the gamma-ray direction; the image brightness corresponds to the gamma-ray energy. Using multiple telescopes to make stereoscopic observations improves the experimental performance.
Cherenkov Telescopes: H.E.S.S. and CTA
The High Energy Stereoscopic System (H.E.S.S.) is an array of five IACTs located in the Khomas Highlands of Namibia, currently the only IACT facility in the Southern hemisphere. Since 2013 I have been active within the H.E.S.S. collaboration, particularly in the analysis of pulsar wind nebulae and of calibration using muons.
The Cherenkov Telescope Array (CTA) is a next generation facility for the detection of the most energetic gamma-rays from space, signatures of astrophysical particle acceleration.
CTA will comprise more than 100 telescopes of three different sizes; large, medium and small; with mirror diameters of 23m, 12m and 4m respectively. Since 2014, I have been active within the CTA consortium, particularly in software development for calibration and data analysis.
Particle Detector Arrays: SWGO
Particle detector arrays such as HAWC, LHAASO or the future Southern Wide-field Gamma-ray Observatory (SWGO) also observe extensive air showers – but by measuring the particles in situ. They are hence located typically at higher altitudes than IACTs and can operate continuously day and night, making them ideal survey instruments.
Pulsar Wind Nebulae
Pulsar Wind Nebulae are a common source class of astrophysical very high energy (VHE) gamma-rays.
Copious amounts of leptons (electrons and positrons) are produced in the immediate environment of the pulsar. These leptons interact with the surrounding medium to produce gamma-rays, detectable at Earth.
The leptons lose energy as they travel away from the source, leading to signature energy-dependent morphology, such as seen in the pulsar wind nebulae HESS J1825-137. This can be used to derive the particle transport mechanism and speed.
Muons with Cherenkov Telescopes
Muons produce easily identifiable ring-shaped images in Cherenkov telescopes when hitting the mirror dish. However, as the distance of the muon from the mirror dish increases, less of the ring is seen, making muons harder to identify.
Muons form a constant brightness light source and are images of full rings used to calibrate the light collection efficiency of Imaging Atmospheric Cherenkov Telescopes.
Improving the identification of partial muon rings enables measurements of the muon production rate and distribution within extensive air showers, currently uncertain quantities.