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

De-Hua Wang, Cheng-Min Zhang, Shuang-Qiang Wang

Published 2019-10-18Version 1

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 (Edot) distributions of the MSPs observed at the wavebands of radio, X-ray, and {\gamma}-ray. We find that all but one (119/120) of the {\gamma}-ray MSPs have been detected with the radio signals (radio+{\gamma} MSPs); on the contrary, nearly half of the radio MSPs (118/237) have not been detected with {\gamma}-rays (radio-only MSPs). In addition, the radio+{\gamma} MSPs are shown to be the relative faster and more energetic objects (<P> ~ 3.28 ms and <Edot> ~ 4.5 * 10^34 erg s^-1) compared with the radio-only MSPs (<P> ~ 4.70 ms and <Edot> ~ 1.0 * 10^34 erg s^-1), 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+{\gamma} signals, which share the faster spin (<P> ~ 2.78 ms) and larger spin-down power (<Edot> ~ 4.1 * 10^34 erg s^-1) distributions than the non-eclipsing ones (<P> ~ 4.19 ms, <Edot> ~ 2.4 * 10^34 erg s^-1), implying the radio+{\gamma} 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.