Study of {^{26}Al}$ in the COSI 2016 Superpressure Balloon Flight

Abstract

The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope designed to survey the -ray sky from 0.2 to 5 MeV. COSI's wide field-of-view (FOV) and excellent energy resolution from high-purity germanium detectors make it uniquely capable of probing this under-explored energy regime. In particular, it can facilitate understanding of stellar nucleosynthesis through studies of diffuse emission from the radioisotope 26 Al at 1.809 MeV. In 2016, COSI was launched from Wanaka, New Zealand on a NASA superpressure balloon and flew for 46 days. The flight was a technologic and scientific success, boasting live detection and polarization studies of GRB160530A, spectral analysis of the Crab Nebula and the 511-keV positron annihilation emission at the Galactic Center, and detection of Cygnus X-1. This article details the first maximum-likelihood search for the 1.809 MeV signature of Galactic 26 Al in the 2016 data. The analysis reveals a promising excess around the expected energies of an 26 Al signature with 3.7 significance and a measured flux of (17.0 ± 4.9) × 10 −4 ph cm −2 s −1 . Further exploration is currently underway to solidify the measurement.

ICRC 2021: Gamma-ray Direct Rapporteur

“…Several analyses looking at the galactic center (GC) including first results from DAMPE of the Fermi Bubbles [30] and GC lines [31], the GC as a high-energy particle accelerator [32], modeling neutral atomic Hydrogen to improve the GC fit [33], Galactic CO maps [34], Al-26 spectroscopy in the Galaxy [35], Cosmic-ray acceleration sites in the galaxy [36,37], and adaptive template fitting to understand the Fermi GC excess [38].…”

Calibrations of the Compton Spectrometer and Imager

“…A complete overview of the flight is provided in [7]. COSI observed the 511 keV annihilation signature at the Galactic Center [8,9], set a constraining upper limit on the polarization of GRB160530A [10], detected the Crab pulsar [11], and measured Galactic 26 Al [12,13]. Studies of other MeV point sources, such as Centaurus A, Cygnus X-1, and the Vela pulsar, are currently underway.…”