Study of the in-flight calibration of theSVOM/ECLAIRs instrument

University essay from Luleå tekniska universitet/Institutionen för system- och rymdteknik

Author: Jakob Östberg; [2020]

Keywords: Telescope; calibration; gamma-ray; burst; ECLAIRs; SVOM; IRAP;

Abstract: The Space based multi-band Variable astronomical Object Monitor (SVOM) is a x- andgamma-ray telescope with the primary objective of observing gamma-ray bursts. Themission is a cooperation between the French and Chinese space agencies and will be launchedin 2021. Gamma-ray bursts are highly variable and energetic electromagnetic radiation thatare generally created due to the collapse of a heavy star into a black hole or neutron star or amerger of two neutron stars. These extreme events appear as bright and short bursts of x- andgamma-rays followed by a longer-lived multi-wavelength afterglow emission. A gamma-rayburst can last from a few milliseconds up to a few thousands of seconds. Thanks to theirbrightness, they can be observed very far from Earth and therefore be used as cosmologicalprobes to study the content of the early Universe. The satellite got a wide-field instrument,ECLAIRs that is in charge of detecting gamma-ray bursts and communicate their locationsto the satellite and ground based telescopes which will repoint towards the gamma-ray burstto observe it. This will allow the gamma-ray bursts to be observed at multiple wavelengthssimultaneously. ECLAIRs is a coded mask, photon counting instrument with the spectralrange of 4 to 150 keV. The readout analog/digital electronics will measure the energy ofeach detected photon hitting the detection plane and encode it as a digital number (channel).To translate this digital number to a physical unit (keV) for scientific analysis purposes, thedetectors are calibrated before launch by irradiating them with radiation from radioactivesources. During the lifetime of the spacecraft, the detectors will age due to the radiationenvironment and the channel to keV relationship will change over time. Therefore, it isnecessary to periodically calibrate the detectors in flight. This is done by taking advantageof the fluorescence lines that always occur in the spectrum at the same energy regardless ofthe background spectrum. These lines are identified with spectral fitting techniques.The aim of my internship is to study the best way to perform such a in-flight calibration. Iinvestigate the need for implementing a data selection process to create the input data andthe minimum amount of data required to recalibrate the channel to keV ratio. I also estimatethe accuracy with which the reconstruction of the energy scale is done and I discuss if it iscompliant with the instrument scientific requirements.

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