The Study On The Profile-variability Of The Millisecond Pulsar

Pulsars are neutron stars with stable self-rotation and strong magnetic field. With its precise periodic, a stable integrated pulsar profiles is sum of many single pulses in cycle of the pulsar period at the same frequency. Pulsar’s profile is a direct observable parameter, which are divided into single, double, triple and multiple peaks as they appear. Many models of radio beam are established, which can explain simple symmetric single profile, double profile and triple profile. The research about the stability of integrated pulsar profiles of pulsars is a very important subject. it will help study radio emission mechanism and emission zone structure of pulsars, improve the pulsar timing precision. Previous studies found that a few pulsars show some profile variabilities. There are two important kinds of the pulse profile variabilities, which all affect the observational characteristics of the pulsar. One is the mode changing. The pulsar has two stable integrated pulse profiles of different forms, normal mode and abnormal mode respectively, the integrated profile switches between two different forms. Another is called nulling phenomenon, that the radio emission of pulsar will suddenly stop in continuous many periods, temporary undetectable pulsar signal, and then return to normal state of emission. After the end of nulling, significant changes of intensity and phase center in single pulse may be observed.The change of integrated pulse profile of pulsar is also reflected in their pulse width and the relative intensity between different components changes with different frequency. The profiles of both normal pulsar and millisecond pulsar varie by the different frequency, but the profile of millisecond pulsar change is relatively more complicated. The pulse component widths and component separations follow evolution with frequency. In some cases these parameters increase and in other cases they decrease with increasing frequency. The reason of variation of pulsar’s emission intensity may be due to the intrinsic of characteristics the pulsar, and also the propagation of radio emission of pulsar through the interstellar medium, which the turbulence of electron density causes the change of flux density at different frequency. This phenomenon is called scintillation.In this article, we researched the stability of the integrated pulse profile of PSR J1022+1001, which shows the double peak structure. At frequencies near 1400 MHz, it has two typical integrated pulse profiles with peak ratio less than 1 and greater than 1. We found that when the whole bandwidth is divided to eight sub-bandwidths, the pulse profile of each sub-bandwidth varies by frequency. The ratio of two peaks increases with increasing frequency. The flux density varies with frequency caused by the interstellar scintillation. When the total profiles are weighted sum of pulse profiles at all sub-bandwidths, it will show two situations, which the peak ratio less than 1 and greater than 1. The analysis suggests that the instability of the integrated pulse profile of the pulsar is mainly due to the variation of the pulse profile by frequency, and the flux density varies with frequency caused by the interstellar scintillation. We also found that in some special cases, the profile changes even at the same sub-frequency, therefore the instability of small part of pulse profile may be due to the intrinsic of characteristics the pulsar or the other reasons.