Skip to Main content Skip to Navigation
Theses

Étude de l'annihilation électron-positon dans la région du centre Galactique avec le spectromètre INTEGRAL/SPI

Abstract : A spectral feature was detected in 1970 in the gamma-ray emission from the central regions of the Milky Way, during balloon flight observations. Located near 511 keV, this feature was soon attributed to the gamma-ray line tracing the annihilation of electrons with their anti-particules, positrons. However, none of the multiple astrophysical scenarii contemplated to explain the production of positrons in the Galactic bulge has been able to reproduce the high injection rate deduced from the flux of the 511 keV line, close to ten to the fourty-third positrons per second.
Launched in 2002, the European gamma-ray satellite INTEGRAL was provided with a spectrometer, SPI, whose unprecedented imaging and spectral capabilities in this energy range enable us to further study the source of the 511 keV line detected in the Galactic centre region.
Indeed, a better determination of the spatial extent of the source, the intrinsic width of the line and the fraction of positrons annihilating in-flight, directly or via the formation of ortho-Positronium atoms, would improve our knowledge of both the annihilation medium and the initial source of positrons, and could allow us to discriminate between the various explanatory scenarii.
The first part of this thesis deals with a key ingredient in the extraction of the annihilation spectrum : the optimization of the instrumental background model. New data screening and tracer selection procedures are presented. Classical multi-linear models are compared to neural and bayesian networks. Finally, three years of observation are used to constrain the width of the source and derive its spectrum.
The second part of the thesis focuses on one of the possible scenarii explaining the high positron injection rate deduced from the flux of the 511 keV line : the annihilation of light dark matter particles into electron-positron pairs. The various radiation mechanisms involved are modeled and confronted to observations in order to set an upper limit on the injection energy of positrons -- e.g. on the mass of the light dark matter particle -- found to vary between 3 and 7.5 MeV, depending on the degree of ionization of the interstellar medium.
Complete list of metadatas

https://tel.archives-ouvertes.fr/tel-00155586
Contributor : Patrick Sizun <>
Submitted on : Monday, June 18, 2007 - 3:58:50 PM
Last modification on : Monday, October 19, 2020 - 11:10:57 AM
Long-term archiving on: : Thursday, April 8, 2010 - 8:40:25 PM

Identifiers

  • HAL Id : tel-00155586, version 1

Collections

Citation

Patrick Sizun. Étude de l'annihilation électron-positon dans la région du centre Galactique avec le spectromètre INTEGRAL/SPI. Astrophysique [astro-ph]. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00155586⟩

Share

Metrics

Record views

643

Files downloads

2480