Isolated Millisecond Pulsars Formed By The Coalescence Of A Neutron Star And A Massive White Dwarf

The isolated millisecond pulsars（IMSPs）lost their companions in millisecond pulsars（MSPs）whose pulse periods are～1.4 to 20 ms.About 1/3 of MSPs are isolated.The origin of these IMSPs is still on open problem.As we know,several possible formation scenarios have been proposed:（1）The merger of neutron star（NS）and massive white dwarf（WD）.（2）Relative winds come from NS evaporating its companion.（3）The MSP can form in high-mass X-ray binaries,and IMSPs can be produced when these binaries are disrupted by core-collapse supernova of the massive companions of these MSPs.（4）In triple star systems,it is possible to form an IMSP by dynamical mass transfer.However,the timescale used in the secondary channel is longer than Hubble time and the contribution of the last two channels to the total IMSP’s population is too small.We are mainly concern about the model of a NS and a WD.Disastrous process and the violent explosions must be resulted by the merger of NS and massive WD.Subluminous type I supernova or long Gamma-ray bursts without accompanying supernova are related to the merger in the forth channel.Understanding this reasonable model in theory plays the key factor for the development and improvement of the theory about stellar structure and evolution.In this thesis,we investigate the formation of IMSPs in close binaries,and discuss the properties of interaction in NS and WD systems,as well as,the phenomenon of long Gamma-ray bursts without accompanying supernova.We use Monte Carlo Simulation method and the rapid binary evolution code to simulate the evolutions of 1×10⁷binary systems.We estimate that the Galactic birth rate of merger for NS and WD is about 5.8×10^-5-2.0×10^-4yr^-1,which is consistent with the previous estimate.We also compare our results with observational date and simulation results.We have made a detailed estimate about the masses and spins for IMSP in our model.The predicted masses are between 1.5M_⊙-2.0M_⊙,which are higher than masses of normal pulsars,while mentioned the spin distributions for IMSPs,the peaks predicted in our models are slower than those of the observations.The main reason may be our overestimating magnetic fields.However,there is no available model to simulate it.