298 articles – 2332 Notices  [english version]
 HAL : in2p3-00585161, version 1
 arXiv : 1003.3588
 Astronomy and Astrophysics 524 (2010) A75
 A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope
 Fermi-LAT Collaboration(s)
 (12/2010)
 Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular clusters. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices $(0.7 < \Gamma <1.4)$ and clear evidence for an exponential cut-off in the range 1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices $(1.0 < \Gamma < 1.7)$, however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters, commensurate with previous estimates. The observation of high-energy gamma-ray emission from a globular cluster thus provides a reliable independent method to assess their millisecond pulsar populations that can be used to make constraints on the original neutron star X-ray binary population, essential for understanding the importance of binary systems in slowing the inevitable core collapse of globular clusters.
 Thème(s) : Physique/Astrophysique/Phénomènes cosmiques de haute energiePlanète et Univers/Astrophysique/Phénomènes cosmiques de haute energie
 Mot(s)-clé(s) : pulsars: general / globular clusters: general / gamma rays: general
 Lien vers le texte intégral : http://fr.arXiv.org/abs/1003.3588
 in2p3-00585161, version 1 http://hal.in2p3.fr/in2p3-00585161 oai:hal.in2p3.fr:in2p3-00585161 Contributeur : Virginie Mas <> Déposé pour le compte de : David Smith <> Soumis le : Lundi 11 Avril 2011, 23:14:14 Dernière modification le : Mardi 12 Avril 2011, 11:32:26