Population study for gamma-ray pulsars; II Millisecond pulsars

Abstract

The population of $\gamma$-ray emitting millisecond pulsars (MSPs) is studied by using Monte-Carlo techniques. We simulate the Galactic distributions of the MSPs, and apply the outer gap model for the $\gamma$-ray emission from each simulated MSP. We take into account the dependence of the observed $\gamma$-ray flux on the viewing angle and inclination angle, which is the angle between the rotation axis and the magnetic axis, respectively. Using the sensitivity of the six-month long observation of the $Fermi$ telescope and radio sensitivities of existing pulsar surveys, 9-13 radio-selected and 22-35 $\gamma$-ray-selected pulsars are detected within our simulation. The statistical properties of the simulated population are consistent with the $Fermi$ observations. Scaling the observed sensitivity $\propto \sqrt{T}$, where $T$ is the length of observation time, the present model predicts that over the 5-year mission $Fermi$ would detect 15-22 radio-selected $\gamma$-ray MSPs, and 95-152 $\gamma$-ray-selected MSPs. Our simulation also predicts that about 100 (or 200-300) $\gamma$-ray MSPs with a flux larger $F\ge 10^{-11}erg/c{\mathrm{m}}^2\mathrm{s}$ (or $5\times 10^{-12}erg/c{\mathrm{m}}^2\mathrm{s}$) irradiate the Earth. With the present sensitivities of the radio surveys, most of them are categorized as $\gamma$-ray-selected pulsars, indicating that most of the $\gamma$-ray MSPs have been missed by the present $Fermi$ observations. We argue that the Galactic $Fermi$ unidentified sources located at high latitudes should be dominated by MSPs, whereas the sources in the galactic plane are dominated by radio-quiet canonical pulsars.

30 pages, 10 figures, accepted for publication in MNRAS

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Cited by in corpus (5)

• Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar
• X-ray and Gamma-ray Emissions from Different Evolutionary Stage of Rotation Powered Millisecond Pulsars
• Probing gamma-ray emissions of Fermi-LAT pulsars with a non-stationary outer gap model
• Population study for gamma-ray pulsars: (III) Radiation characteristics and viewing geometry
• Constraints on the Emission Geometries of Gamma-ray Millisecond Pulsars Observed with the Fermi Large Area Telescope