Search For Orbital Modulated ?-ray Emission From Black Widow And Redback Millisecond Pulsars

Both Black widow(BW)and Redback(RB)belong to a special class of millisecond pulsar binaries.Their companion stars are evaporated by the pulsar's radiation and the system can eventually form an isolated millisecond pulsar.They often have multi-band radiation(optical,UV,IR,X-ray,?-ray)and orbital modulation.However,the current research has two problems: one is the insufficient number of samples of orbital modulation,and the other is that the significance of the orbital modulation is low(about 3?).This limits the model constraining and discrimination as well as our understanding of such systems.On the other hand,in recent years,as a series of astronomical equipments has been put into operation,a lot of observational data has been accumulated.Therefore,there is an urgent theoretical need to search for orbital modulation of such sources.We hope that by adding RB/BW samples with orbital modulation,we can constrain and discriminate the existing models better.For the existing RB / BW systems,we assume that the modulation is mainly caused by the inverse Compton scattering emission(ICS).If the ICS flux is higher,the modulation is more likely to exist.By using the Fermi-LAT gamma-ray data,we searched for the modulation of three sources by investigating the spectral energy distribution and light curves.We found that there is no significant orbital modulation in the ? –ray emission of PSR J1810+1744.However,PSR J2256-1024 and PSR J2215+5135 both show significant orbital modulation(> 4?)at lower energy band.In addition,we analyzed and compared the data of both PSR J2256-1024 and PSR J2215+5135 in different pulse phases,time periods and energy bands,and found that the orbital modulation of the former is mainly related to the second peak of the pulse,while the latter's orbital modulation seems to be mainly related to the first peak of the pulse.Moreover,we found that there is a long-term change of the significance of orbital modulation of PSR J2256-1024 on the time scale of year from weak to strong,then to weak again(nearly disappeared).All these findings are reported for the first time.What's more,when performing light curve analysis on the surrounding bright sources of PSR J2256-1024 and PSR J2215+5135 to eliminate their contaminations,multiple flares were found.