3 sujets IRFU

Dernière mise à jour : 19-01-2020


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• Astroparticles

 

STUDY OF THE MULTI-SCALE VARIABILITY OF THE VERY HIGH ENERGY GAMMA-RAY SKY

SL-DRF-20-0336

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe Astroparticules (GAP)

Saclay

Contact :

Francois BRUN

Jean-François Glicenstein

Starting date : 01-10-2020

Contact :

Francois BRUN
CEA - DRF/IRFU/DPHP/HESS 2


Thesis supervisor :

Jean-François Glicenstein
CEA - DRF/IRFU/DPHP/HESS 2

0169089814

Laboratory link : http://irfu.cea.fr/dphp/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3429

More : https://www.mpi-hd.mpg.de/hfm/HESS/

Very high energy gamma ray astronomy observes the sky above a few tens of GeV. This emerging field of astronomy has been in constant expansion since the early 1990s, in particular since the commissioning of the H.E.S.S. array in 2004 in Namibia. IRFU/CEA-Paris Saclay is a particularly active member of this collaboration from the start. It is also involved in the preparation of the future CTA observatory (Cherenkov Telescope Array), which should come into operations by 2024. The detection of gamma rays above a few tens of GeV makes it possible to study the processes of charged particles acceleration within objects as diverse as supernova remnants or active galactic nuclei. Through this, H.E.S.S. aims in particular at answering the century-old question of the origin of cosmic rays.



HESS allows measuring the direction, the energy and the arrival time of each detected photon. The time measurement makes it possible to highlight sources which present significant temporal or periodic flux variations. The study of these variable emissions (transient or periodic), either towards the Galactic Center or active nuclei of galaxies (AGN) at cosmological distance allows for a better understanding of the emission processes at work in these sources. It also helps characterizing the medium in which the photons propagate and testing the validity of some fundamental physical laws such as Lorentz invariance. It is possible to probe a wide range of time scales variations in the flux of astrophysical sources. These time scales range from a few seconds (gamma ray bursts, primordial black holes) to a few years (binary systems of high mass, active galaxy nuclei).

One of the major successes of the first decade of data collection of H.E.S.S. was to conduct the first Galactic Plan survey of sources in this energy range. This survey, comprising more than 10 years of data, combines observations dedicated to known sources, such as the Galactic Center or some supernova remnants, as well as blind observations for the discovery of new sources. The subject of the thesis proposed here deals with one aspect of the study of the Galactic plane that remains to be explored: research and study of the variability and periodicity of gamma-ray sources throughout this dataset.

High-energy multi-messenger astrophysics with H.E.S.S. and CTA

SL-DRF-20-0001

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe Astroparticules (GAP)

Saclay

Contact :

Fabian Schussler

Starting date : 01-09-2020

Contact :

Fabian Schussler
CEA - DRF/IRFU/DPHP/GCOSMO

+33169083020

Thesis supervisor :

Fabian Schussler
CEA - DRF/IRFU/DPHP/GCOSMO

+33169083020

Personal web page : http://irfu.cea.fr/Pisp/fabian.schussler/index.html

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3709

Very recently a fundamentally new domain of astronomy and astrophysics has shown its first results: multi-messenger and real-time astrophysics. The simultaneous detection of various new astrophysical messengers (gravitational waves, high-energy gamma rays and high-energy neutrinos) and the exchange and combination of data from very different observatories allows to open new windows and provides unprecedented insights into the most violent phenomena ever observed.

New and significant conclusions can be obtained by combining these new messengers. Joint analyses of archival observations in different wavelengths have brought enormous insights in the past and, as this technique provides an assured and certain scientific return, it will also be used in the proposed thesis project. At the same time it has becomes clear that another important step does greatly enhance the sensitivity of multi-messenger searches: the need to gain full access to the wealth of information provided by analyzing and combining the data in real-time. The proposed thesis project will allow opening this new window to the high-energy universe: real-time multi-messenger astronomy at very high energies. The combination of the various particles and radiations in a truly multi-messenger online alert system will resolve several challenges faced in high-energy astrophysics and especially allow detecting and studying violent transient phenomena that are supposed to be at the origin of high-energy cosmic rays. The project will introduce the time domain to high-energy astrophysics and has the potential to cause a paradigm shift in how observations and data analyses are performed.

The core of the proposed project will be H.E.S.S., currently the world’s most sensitive gamma-ray instrument, and CTA, the next generation, global high-energy gamma-ray observatory. We’ll combine their data with events recorded by IceCube, the world’s largest neutrino telescope and the advanced Virgo and Ligo gravitational wave interferometers. The detection of a transient high-energy gamma-ray source in coincidence with gravitational waves or high-energy neutrinos will provide the long sought evidence for their common origin and may resolve the century old quest for the origin of high-energy cosmic rays.

We’ll also collaborate with the world’s most sensitive radio observatories (e.g. the SKA precursors MeerKAT and ASKAP) to search for counterparts to Fast Radio Bursts and in general study a large variety of messengers like Gamma-Ray Bursts or flares from active galactic nuclei. By scanning the data acquired with high-energy gamma-ray observatories in real-time, it will also possible to send alerts to the wider astronomical community to ensure simultaneous observations at other wavelengths.

Dark energy and cosmological constraints with emission line galaxies in the spectroscopic survey DESI

SL-DRF-20-0972

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe Cosmologie (GCOSMO)

Saclay

Contact :

Vanina RUHLMANN-KLEIDER

Etienne Burtin

Starting date : 01-10-2020

Contact :

Vanina RUHLMANN-KLEIDER
CEA - DRF/IRFU/DPHP/GCOSMO

01 69 08 61 57

Thesis supervisor :

Etienne Burtin
CEA - DRF/IRFU/DPHP/GCOSMO

0169085358

The late acceleration of the Universe expansion, revealed at the end of the 1990s and confirmed since then with more precise cosmological data, remains unexplained. Modifications to General Relativity at large scales offer a promising explanation. Among the measures, that of the growth rate of structures is the most direct way to test the predictions of General Relativity, since gravity is the driving force behind this growth. This PhD proposes to use observations of the recently commissioned DESI spectrograph to measure the clustering of emission line galaxies, the main tracer of DESI. The aim is to derive a measurement of the growth rate of structures and to compare it with General Relativity predictions in order to search for possible deviations.

The thesis will take place at Irfu, the Institute for Research on the Fundamental laws of the Universe. The PhD student will join the cosmology group of Irfu/DPhP, composed of 9 physicists, 6 PhD students and 2 post-docs. Actively involved in the eBOSS and DESI experiments, the group also participates in Euclid and has in the past had a strong contribution in the SNLS, Planck and BOSS international collaborations. The future PhD student will be integrated into the DESI collaboration and will benefit from all the group’s expertise acquired on BOSS and eBOSS.

 

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