Seminar by Maria Edvige Ravasio and Gor Oganesyan
Zoom - February 20, 2025 - 15.00
WEBINAR LINK
Title: Discovery of a bright MeV emission line in the brightest GRB ever detected.
Abstract: With its record-breaking fluence, GRB 221009A provided several unique opportunities to investigate the multi-wavelength emission of a gamma-ray burst with unprecedented detail. In this talk, we will present the discovery of a transient spectral line at MeV energies in the Fermi/GBM data of GRB 221009A, standing distinctively above the continuum of the prompt emission spectrum. This highly-significant (>6 sigma), luminous (~10^50 erg/s), and narrow (width~1 MeV) feature shows a consistent temporal evolution, becoming softer and dimmer over ~80 seconds. This represents the first detection of an emission line at MeV energies in the prompt emission spectrum of a gamma-ray burst.
We will discuss the various interpretations of this spectral feature, with the leading one being a blue-shifted annihilation line of electron-positron pairs. The detailed study of the physical conditions allowing for its presence offers key insights into the poorly understood jet composition and the dissipation processes powering the GRB emission. (https://ui.adsabs.harvard.edu/abs/2024Sci...385..452R/abstract)