Investigation on the Binary Millisecond Pulsars at Radio and γ-Ray Wavelengths: Links with the Orbital Parameters

We analyze the properties of the binary millisecond pulsars (BMSPs), detected at radio and γ-ray wavelengths, and further probe their correlations with the binary orbital parameters and companion masses to trace the possible evolutionary histories. We find that the BMSPs with the lowest-mass companions, (0.006-0.06)M , have short orbital periods Porb < 1 day and in most cases (23 out of 25) have been detected in both radio and γ-rays. On the other hand, the BMSPs with companion masses Mc = (0.06-0.4)M have a much larger Porb range, from 0.1 to 200 days, and nearly half of them show radio+γ (53 out of 103), while the remaining ones emit only radio waves. We suggest that the two groups, with low-mass and more massive companions, respectively, experienced different evolutionary histories. Concerning the sources with the more massive companions, the radio+γ BMSPs have on average significantly shorter spin periods ( 〈 P 〉 = 3.37 ms) than the radio-only BMSPs ( 〈 P 〉 = 4.73 ms). We propose that the latter systems are a later evolutionary phase of the former ones.