Investigation of the Millisecond Pulsar Origins by their Spin Periods at the Wavebands of Radio, X-Ray, and γ-Ray

Abstract

To track the formation and evolution links of the millisecond pulsars (MSPs) powered by accretion and rotation in the Galactic field, we investigate the spin period (P) and spin-down power () distributions of the MSPs observed at the wavebands of radio, X-ray, and γ-ray. We find that all but one (119/120) of the γ-ray MSPs have been detected with the radio signals (radio+γ MSPs); on the contrary, nearly half of the radio MSPs (118/237) have not been detected with γ-rays (radio-only MSPs). In addition, the radio+γ MSPs are shown to be the relative faster and more energetic objects ( and ) compared with the radio-only MSPs ( and ), while the spin periods of these two MSP populations are compatible with the log-normal distributions by the statistical tests. Most rotation-powered MSPs (RMSPs) with the radio eclipsing (31/34) exhibit the radio+γ signals, which share the faster spin () and larger spin-down power () distributions than the non-eclipsing ones (, ), implying the radio+γ MSPs to be younger than the radio-only MSPs. It is noticed that the spin distribution of the accretion-powered X-ray MSPs shows a clustering phenomenon around ∼1.6–2.0 ms, which is not observed in RMSPs, hinting that the RMSPs may experience the multiple possible origins. Particularly, all the three super-fast spinning RMSPs with P ∼ 1.4–1.6 ms exhibit the non-eclipsing, and we argue that they may be the distinctive sources formed by the accretion induced collapse (AIC) of white dwarfs.