Constraints on the Emission Geometries of Gamma-ray Millisecond Pulsars Observed with the Fermi Large Area Telescope

摘要

Millisecond pulsars (MSPs) have been established as a class of high-energy($\geq$0.1 GeV) emitters with the Large Area Telescope (LAT) aboard the\emph{Fermi Gamma-ray Space Telescope}. Most MSP gamma-ray light curves displaysharp peaks indicative of thin accelerating gaps, suggesting copiouspair-creation in the open volume. MSP gamma-ray and radio light curves havebeen simulated using geometric outer-gap (OG), slot-gap/two-pole caustic (TPC),and pair-starved polar cap gamma-ray models and either a hollow-cone beam oraltitude-limited, outer-magnetospheric gap radio model, all assuming a vacuumretarded dipolar magnetic field geometry. A Markov chain Monte Carlo maximumlikelihood technique has been developed to find the best-fit model parametersfor nineteen MSPs using data from the LAT and various radio observatories. Thebest-fit viewing angles follow a uniform, angular distribution. Thedistribution of magnetic inclination angles favors all angles equally, contraryto analyses of non-recycled pulsars, which supports the theory that MSPs havebeen spun-up via accretion. There are suggestions that the radio emissionshould occur nearer the light cylinder. These results have implications for MSPpopulation simulations and for addressing MSP contributions to diffusebackgrounds. An implied transition in the gamma-ray luminosity versus spin-downpower trend is observed but more statistics are necessary to describe it.