${}^{26}$Al gamma rays from the Galaxy with INTEGRAL/SPI

Abstract

The presence of radioactive ${}^{26}$Al at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way. Diffuse emission from its decay can be measured with gamma-ray telescopes in space. The intensity, line shape, and spatial distribution of the ${}^{26}$Al emission allow a study of these nucleosynthesis sources. The line parameters trace massive-star feedback in the interstellar medium due to its 1~My lifetime. We aim to deepen previous studies of the ${}^{26}$Al emission in the Milky Way, using all gamma-ray data including single and double events as collected with SPI on INTEGRAL from 2003 until 2020. We apply improved spectral response and background as evaluated from tracing spectral details over the entire mission. The exposure for Galactic ${}^{26}$Al emission is enhanced using all event types measured within SPI. We re-determine the intensity of Galactic ${}^{26}$Al emission across the entire sky, through maximum likelihood fits of simulated and model-built sky distributions to SPI spectra for single and for double detector hits. We find an all-sky flux of (1.84$\pm$0.03$)\times$10${}^{-3}$~ph~cm${}^{-2}$s${}^{-1}$ in the 1.809~MeV line from ${}^{26}$Al, determined as fitted to sky distributions from previous observations with COMPTEL. Significant emission from higher latitudes indicate an origin from nearby massive-star groups and superbubbles, also supported by a bottom-up population synthesis model. The line centroid is found at (1809.83$\pm$0.04~keV, and line broadening from source kinematics integrated over the sky is (0.62$\pm 0.3$)~keV (FWHM).

7 pages, 9 figures. Accepted for publication in Astronomy & Astrophysics

References in corpus (10)

• Star formation near the Sun is driven by expansion of the Local Bubble
• Spectral and intensity variations of Galactic 26^Al emission
• The Galactic ${}^{26}$Al emission map as revealed by INTEGRAL/SPI
• 26Al kinematics: superbubbles following the spiral arms? Constraints from the statistics of star clusters and HI supershells
• Gamma-ray Emission of 60Fe and 26Al Radioactivities in our Galaxy
• Background modelling for $\gamma$-ray spectroscopy with INTEGRAL/SPI
• Comparing simulated ${}^{26}$Al maps to gamma-ray measurements
• Galactic 26Al traces metal loss through hot chimneys
• Measurement of Galactic ${}^{26}$Al with the Compton Spectrometer and Imager
• Galactic Population Synthesis of Radioactive Nucleosynthesis Ejecta

Cited by in corpus (5)

• Evolution of radioactive elements in the LMC: predictions for future gamma-ray surveys
• Imaging the positron annihilation line with 20 years of INTEGRAL/SPI observations
• Gamma-ray line emission from the Local Bubble
• Enhancing Compton telescope imaging with maximum a posteriori estimation: a modified Richardson-Lucy algorithm for the Compton Spectrometer and Imager
• Nuclear astrophysics