275 Observation and modeling of the galactic positron annihilation emissions

Job title:

275 Observation and modeling of the galactic positron annihilation emissions

Company:

Centre National d’Etudes Spatiales

Job description

25-275 Observation and modeling of the galactic positron annihilation emissionsPostuler25-275 Observation and modeling of the galactic positron annihilation emissions

• Doctorat, 36 mois
• Temps plein
• Indifférent
• Maitrise, IEP, IUP, Bac+4
• Astronomy, Astrophysics

PostulerMissionSince its discovery in the 1970s, a positron (the anti-particle of the electron) annihilation emission has been observed in the central regions of our Galaxy by various gamma-ray telescopes. The origin of these positrons remains a mystery; the sources considered to date (radioactive isotopes, jets from compact objects, cosmic rays, dark matter…) are unable to fully explain the properties of the annihilation emission. The latest observations made with the SPI spectrometer onboard the INTEGRAL space observatory in the middle 2010s show that the emission comes mainly from the galactic bulge, with a diffuse contribution from the disk. Even if the emission morphology is not well constrained so far, this spatial distribution, which has no equivalent at other wavelengths, is unlike any known source distribution. On the spectral side, the annihilation emissions is composed of a 511 keV line, an orthopositronium continuum at photon energy lower than 511 keV (due to annihilation of positron-electron bound states) and a continuum at high energy (
511 keV) due to the annihilation in-flight of relativistic positrons. While the two first components have been clearly observed, the annihilation in-flight has not yet been detected. Its detection would provide the maximum energy of positrons responsible of the annihilation emission. The shape of the line and the fraction of the emission in the orthopositronium continuum depend on the physical conditions (temperature, ionization fraction, abundances) in which low energy positrons annihilate.The aim of the PhD is to prepare the scientific analysis of positron annihilation signatures with COSI (COmpton Spectrometer & Imager), NASA’s future gamma-ray telescope, which will be launched into orbit in August 2027. This preparation consists on the one hand of the modelling of the spatial and spectral gamma-ray emission from positron annihilation on the basis of current knowledge of Galaxy properties and annihilation physics. The models that the PhD student will develop will be based on the simulation of the transport and the annihilation of positrons in the interstellar medium. It will require a detailed study of the various modes of transport (diffusion, advection, ballistic propagation, etc.), and their modeling, taking into account the physical conditions (turbulence, winds, magnetic fields, etc.) in the interstellar medium. Spectral model will be updated taking into account the latest cross sections. The aim of this effort is to have in hand a state-of-the-art positron annihilation model that will be fundamental for the interpretation of the data from the COSI mission.On the other hand, the PhD student will confront the model to data of INTEGRAL/SPI telescope in order to derive the best pre-COSI constraints on Galactic positron annihilation. One of the tasks will consists in searching for the signature of the annihilation in-flight emission and provide constraints on the maximum kinetic energy of the positrons. Based on over 20 years of data, the PhD student will obtain the most precise determination of the morphology of the annihilation emissions. He will furthermore perform spatially-resolved spectral analyses that will constrain the physical conditions of the medium in which positrons annihilate and its variations throughout the Galaxy.Both the modelling and the data analysis works are expected to lead to several innovative publications. Furthermore, the INTEGRAL observatory is going to be stopped at the end of 2024 and the PhD student will perform an analysis of the entire database that was collected throughout the mission, providing the most stringent characteristics of the Galactic positrons annihilation emission.References:Knödlseder et al., 2005, A&A, 441, 513Jean et al., 2006, A&A, 445, 579Jean et al., 2009, A&A, 508, 1099Prantzos et al., 2010, Review of Modern Physics, 83, 1001For more Information about the topics and the co-financial partner (found by the lab !);contact Directeur de thèse –Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 14th, 2025 Midnight Paris time !

Expected salary

Location

Toulouse

Job date

Wed, 05 Feb 2025 05:45:56 GMT

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