Measurement of Galactic \(^{26}\)Al with the Compton Spectrometer and Imager

The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope designed to survey the 0.2-5 MeV sky. COSI's energy resolution of \(\sim\)0.2% at 1.8 MeV, single-photon reconstruction, and wide field of view make it capable of studying astrophysical nuclear lines, partic...

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Bibliographic Details
Published in:arXiv.org 2022-02
Main Authors: Beechert, Jacqueline, Siegert, Thomas, Tomsick, John A, Zoglauer, Andreas, Boggs, Steven E, Brandt, Terri J, Gulick, Hannah, Pierre, Jean, Kierans, Carolyn, Lazar, Hadar, Alexander, Lowell, Roberts, Jarred M, Sleator, Clio, Peter von Ballmoos
Format: Article
Language:English
Subjects:
Astronomical models
Balloon flight
Energy resolution
Explorer satellites
Field of view
Galactic evolution
Galaxies
Gamma rays
Iterative methods
Massive stars
Nuclear fusion
Sky surveys (astronomy)
Stellar evolution
Superpressure balloons
Telescopes
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Summary:The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope designed to survey the 0.2-5 MeV sky. COSI's energy resolution of \(\sim\)0.2% at 1.8 MeV, single-photon reconstruction, and wide field of view make it capable of studying astrophysical nuclear lines, particularly the 1809 keV \(\gamma\)-ray line from decaying Galactic \(^{26}\)Al. Most \(^{26}\)Al originates in massive stars and core-collapse supernova nucleosynthesis, but the path from stellar evolution models to Galaxy-wide emission remains unconstrained. In 2016, COSI had a successful 46-day flight on a NASA superpressure balloon. Here, we detail the first search for the 1809 keV \(^{26}\)Al line in the COSI 2016 balloon flight using a maximum likelihood analysis. We find a Galactic \(^{26}\)Al flux of \((8.6 \pm 2.5) \times 10^{-4}\) ph cm\(^{-2}\) s\(^{-1}\) within the Inner Galaxy (\(|\ell| \leq 30^{\circ}\), \(|b| \leq 10^{\circ}\)) with 3.7\(\sigma\) significance above background. Within uncertainties, this flux is consistent with expectations from previous measurements by SPI and COMPTEL. This analysis demonstrates COSI's powerful capabilities for studies of \(\gamma\)-ray lines and underscores the scientific potential of future compact Compton telescopes. In particular, the next iteration of COSI as a NASA Small Explorer satellite has recently been approved for launch in 2025.
ISSN:2331-8422
DOI:10.48550/arxiv.2202.11713