Student : MATE Sujay
Advisor : BOUCHET Laurent, ATTEIA Jean-Luc
Start : 2017
Group : GAHEC
Gamma-Ray Bursts (GRBs) are the most luminous explosions in the universe. They are observed as bright flashes of gamma/X-rays (lasting few milliseconds to few tens of seconds) followed by an “afterglow” emission (usually at longer wavelengths). They are produced either due to the merger of two compact objects (a pair of neutron stars or a neutron star and a black hole) or due to the core collapse of a massive star (> 15M ). GRBs are excellent candidates to study physics at extreme energies and densities. They also constitute important astrophysical tools to probe the history of the universe as they are observed at all epochs.
The upcoming (June 2022) Sino-French mission SVOM (Space-based multi-band astronomical Variable Objects Monitor) aims to detect and study GRBs using dedicated space and ground based instruments to obtain multi-wavelength coverage. The primary instrument onboard SVOM spacecraft is ECLAIRs, a wide-field (∼ 2 sr) coded-mask imager sensitive in the 4 – 150 keV energy range. ECLAIRs will detect and localise GRBs (and other high energy transients) in near real time using an onboard trigger.
ECLAIRs will encounter a high and variable background due to the wide field-of-view (FoV) and the pointing strategy of SVOM which makes the Earth transit through the FoV. A new method (called Particle Interaction Recycling Approach or PIRA), based on Monte-Carlo simulations (GEANT4), was developed to estimate the variable background accurately and rapidly. The simulations of the background are complemented with simulations of X-ray sources and gamma-ray bursts to generate complete observation scenarios.
The variable background of ECLAIRs poses challenges to detect GRBs and affects the sensitivity of the instrument. We use the simulated data to evaluate the performance of the onboard trigger, in particular, the impact of the variable background and its sensitivity to the GRB characteristics (duration, temporal profile, spectral shape, position in the FoV).
ECLAIRs will send all detected photons to the ground. In addition, the availability of a larger computational power and the better knowledge of the context (e.g. background variations, sources in the FoV, etc.) on the ground motivates us to develop an “offline trigger” to overcome the challenges faced by the onboard trigger. An algorithm based on wavelet transforms is proposed to detect GRBs as part of the offline trigger.
The work in this thesis, i.e. the development of PIRA, instrument’s performance evaluation and development of a trigger method, provides a sound basis to build an effective offline trigger, that will complement the onboard trigger and improve the overall performance of the SVOM mission.