INTEGRAL/SPI $\gamma$-ray line spectroscopy

Abstract

INTEGRAL/SPI is a space-based coded mask telescope featuring a 19-element Germanium detector array for high-resolution gamma-ray spectroscopy, encapsulated in a scintillation detector assembly that provide a veto for background from charged particles. In space, cosmic rays irradiate spacecraft and instrument, which results in a large instrumental background from activation of those materials, and leads to deterioration of the charge collection properties of the Ge detectors. We use 13.5 years of INTEGRAL/SPI spectra for each detector and for each pointing of the satellite. Spectral fits provide us with details about separated background components. From the strongest background lines, we first determine how the spectral response changes with time. We then determine how the instrumental background components change in intensities and other characteristics, most-importantly their relative distribution among detectors. Spectral resolution of Ge detectors in space degrades with time, up to 15% within half a year, consistently for all detectors, and across the SPI energy range. Semi-annual annealing operations recover these losses, yet there is a small long-term degradation. The intensity of instrumental background varies anti-correlated to solar activity, in general. There are significant differences among different lines and with respect to continuum. Background lines are found to have a characteristic, well-defined and long-term consistent intensity ratio among detectors. We use this to categorise lines in groups of similar behaviour. The dataset of spectral-response and background parameters as fitted across the INTEGRAL mission allows studies of SPI spectral response and background behaviour in a broad perspective, and efficiently supports precision modelling of instrumental background.

arXiv comment30 pages, including 18 figures and an extended table of gamma-ray lines. Accepted for publication in Astronomy and Astrophysics

References in corpus (8)

• SPI/INTEGRAL in-flight performance
• Gamma-ray spectroscopy of Positron Annihilation in the Milky Way
• SN2014J gamma-rays from the 56Ni decay chain
• Kinematics of massive star ejecta in the Milky Way as traced by 26Al
• Nuclear-Astrophysics Lessons from INTEGRAL
• INTEGRAL/SPI ground calibration
• Revisiting INTEGRAL/SPI observations of 44Ti from Cassiopeia A
• INTEGRAL: science highlights and future prospects

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• Cosmic nucleosynthesis: a multi-messenger challenge
• Constraints on positron annihilation kinematics in the inner Galaxy
• Imaging the 511 keV positron annihilation sky with COSI
• First observation of MeV gamma-ray universe with bijective imaging spectroscopy using the Electron-Tracking Compton Telescope aboard SMILE-2+
• Reticulum II: Particle Dark Matter and Primordial Black Holes Limits
• A Physical Background Model for the Fermi Gamma-ray Burst Monitor
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• Potential origin of the state-dependent high-energy tail in the black hole microquasar Cygnus X-1 as seen with INTEGRAL
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• Nucleosynthesis constraints through $\gamma$-ray line measurements from classical novae
• ${}^{26}$Al gamma rays from the Galaxy with INTEGRAL/SPI
• Sub-GeV Dark Matter Annihilation: Limits from Milky Way observations with INTEGRAL
• Galactic Population Synthesis of Radioactive Nucleosynthesis Ejecta
• Radioactive isotopes in the interstellar medium
• New Constraints on Decaying Dark Matter from INTEGRAL/SPI
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• Calibrating SPI-ACS/INTEGRAL for gamma-ray bursts and re-estimating energetics of GRB/GW 190425 in gamma-ray range
• Imaging the positron annihilation line with 20 years of INTEGRAL/SPI observations
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• Enhancing Compton telescope imaging with maximum a posteriori estimation: a modified Richardson-Lucy algorithm for the Compton Spectrometer and Imager
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• Search for Axion-Like Particles from Nearby Pre-Supernova Stars
• Updated Constraints on the Injection Energy of Positrons Generating the Galactic 511 keV $\gamma$-ray line
• Gamma-ray spectroscopy of galactic nucleosynthesis
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