Skip to main content
eScholarship
Open Access Publications from the University of California

UC Berkeley

UC Berkeley Electronic Theses and Dissertations bannerUC Berkeley

Detection of the 511 keV positron annihilation line with the Compton Spectrometer and Imager

  • Author(s): Kierans, Carolyn
  • Advisor(s): Boggs, Steven E
  • et al.
Abstract

The signature of positron annihilation, namely the 511~keV $\gamma$-ray line, was first detected coming from the direction of the Galactic center in the 1970's, but the source of Galactic positrons still remains a puzzle. The measured flux of the annihilation corresponds to an intense steady source of positron production, with an annihilation rate of $\sim$10$^{43}$~e$^+$/s. Spatially, the 511~keV intensity is strongest in the Galactic center region, with an additional component that is consistent with the Galactic disk; however, the unique morphology is not well constrained.

The Compton Spectrometer and Imager (COSI) is a balloon-borne soft $\gamma$-ray (0.2--5~MeV) telescope designed to perform wide-field imaging and high-resolution spectroscopy, with a goal of furthering our understanding of Galactic positrons. COSI employs a compact Compton telescope design, using 12 cross-strip germanium detectors to track the trajectory of incident photons, where position and energy deposits from Compton interactions allow for a reconstruction of the source sky position and significant background reduction.

COSI had a record-breaking 46-day balloon flight from Wanaka, New Zealand, in May--July 2016, and here we report on the detection and analyses of the 511~keV emission from those observations. To isolate the Galactic positron annihilation emission, we have developed a background subtraction technique utilizing the COMPTEL Data Space. With this new method, we find a 7.2~$\sigma$ detection of the 511~\keV line and a broader spatial distribution of the emission than has been previously reported.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View