298 articles – 2332 Notices  [english version]
 HAL : in2p3-00530035, version 1
 arXiv : 1007.1142
 Astrophysical Journal 720 (2010) 272-283
 Fermi LAT observations of the Geminga pulsar
 Fermi-LAT Collaboration(s)
 (01/09/2010)
 We report on the \textit{Fermi}-LAT observations of the Geminga pulsar, the second brightest non-variable GeV source in the $\gamma$-ray sky and the first example of a radio-quiet $\gamma$-ray pulsar. The observations cover one year, from the launch of the $Fermi$ satellite through 2009 June 15. A data sample of over 60,000 photons enabled us to build a timing solution based solely on $\gamma$ rays. Timing analysis shows two prominent peaks, separated by $\Delta \phi$ = 0.497 $\pm$ 0.004 in phase, which narrow with increasing energy. Pulsed $\gamma$ rays are observed beyond 18 GeV, precluding emission below 2.7 stellar radii because of magnetic absorption. The phase-averaged spectrum was fitted with a power law with exponential cut-off of spectral index $\Gamma$ = (1.30 $\pm$ 0.01 $\pm$ 0.04), cut-off energy $E_{0}$ = (2.46 $\pm$ 0.04 $\pm$ 0.17) GeV and an integral photon flux above 0.1 GeV of (4.14 $\pm$ 0.02 $\pm$ 0.32) $\times$ 10$^{-6}$ cm$^{-2}$ s$^{-1}$. The first uncertainties are statistical and the second are systematic. The phase-resolved spectroscopy shows a clear evolution of the spectral parameters, with the spectral index reaching a minimum value just before the leading peak and the cut-off energy having maxima around the peaks. Phase-resolved spectroscopy reveals that pulsar emission is present at all rotational phases. The spectral shape, broad pulse profile, and maximum photon energy favor the outer magnetospheric emission scenarios.
 Thème(s) : Physique/Astrophysique/Phénomènes cosmiques de haute energiePlanète et Univers/Astrophysique/Phénomènes cosmiques de haute energie
 Mot(s)-clé(s) : gamma rays: stars – pulsars: general – pulsars: individual (PSR J0633+1746 – Geminga)
 Lien vers le texte intégral : http://fr.arXiv.org/abs/1007.1142
 in2p3-00530035, version 1 http://hal.in2p3.fr/in2p3-00530035 oai:hal.in2p3.fr:in2p3-00530035 Contributeur : Virginie Mas <> Déposé pour le compte de : David Smith <> Soumis le : Mercredi 27 Octobre 2010, 11:43:04 Dernière modification le : Jeudi 28 Octobre 2010, 09:50:00