Data Centre for Astrophysics
Astronomy Department of the University of Geneva
ISDC Seminar

Thursday, 21 June 2018 at 14:00

Leanne Guy


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Thursday, 7 June 2018 at 14:00

Denis Bernard
Laboratoire Leprince-Ringuet ECOLE POLYTECHNIQUE Route de Saclay 91128 PALAISEAU CEDEX

High-performance gamma-ray astronomy and polarimetry with gamma -> e+e-

conversions in gas detectors.

Abstract. High-sensitivity observations of cosmic sources are scarce in the gap that lies between the domains in which Compton telescopes and pair telescopes are at their best, i.e. in the energy range ~ 0.1 -- 100 MeV. Also gamma-ray polarimetry, which would be such a powerful diagnostic of the process(es) at work in gamma-ray emitters, in particular related to the intensity and to the homogeneity/turbulence of the magnetic field, has never been achieved with e+e- pairs on cosmic sources. I will present how low-density active targets such as gas detectors can improve on the observation of MeV photons and enable (linear) polarimetry. We have characterized a gas time-projection chamber (TPC) prototype on beam and demonstrated for the first time the polarimetry of a MeV gamma-ray beam with a good dilution factor [Astroparticle Physics 97 (2018) 10].

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Wednesday, 28 March 2018 at 14:00

David Smith
CENBG Bordeaux

Gamma Phase-folding a Thousand Pulsars

Abstract. In its 10th year on orbit, the Fermi LAT continues to discover GeV gamma-rays from over 20 pulsars per year. The most sensitive way to find them is to use rotation ephemerides to "phase fold" the gamma photons, to then look whether the resulting phase histogram is flat or not. We are currently doing this for over a thousand radio pulsars, using ephemerides provided by the Parkes, Jodrell Bank, and Nancay radio telescopes. I will present a dozen gamma-ray pulsars found in 2017, and explain how they enhance the sample of over 200 pulsars we already had. I will discuss possible causes of the gamma-ray "deathline" near a spindown power of Edot ~ few 1E33 erg/s. Finally, I will say some words about extrapolating the observed gamma-ray pulsar population to estimate the contribution of unresolved pulsars to the diffuse background.

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