脉冲星VLBI观测软件相关处理进展

The Progress on Correlating Pulsar VLBI Observation Data with Software Correlator

VLBI是进行高分辨率脉冲星观测研究的重要手段。脉冲星信号是非常微弱的脉冲序列,其VLBI观测面临多种挑战。在数据相关过程中采用有效技术提取脉冲星信号可提高观测成功率和精度。DiFX(Distributed FX-style Software Correlator)是目前国际上流行的开源软件相关处理机,它采用非相干消色散技术和"脉冲星数据分箱技术"(Pulsar Binning),在脉冲星VLBI观测数据的相关处理方面具有优异的性能。介绍了DiFX的构架,安装、调试方法,并对利用DiFX处理脉冲星VLBI观测数据的进展情况进行论述。利用单机环境下的DiFX,在普通模式和Pulsar Binning模式下对中国VLBI网(CVN)第一次脉冲星观测数据进行相关处理;利用德国马普射电天文研究所集群计算环境下的Bonn-DiFX,在PulsarBinning模式下对流量仅有2.6 mJy的毫秒脉冲星PSRJ1022+1001的欧洲VLBI网(EVN)观测数据成功进行相关处理。最后,对使用DiFX处理脉冲星观测数据情况进行总结,并展望了今后CVN开展脉冲星观测研究的前景。

VLBI is an important tool to perform high angular resolution observation on pulsars. The signal of most of pulsars is a series of very weak radio pulses, which are affected by interstellar medium and ionosphere heavily. So, some challenges have to be faced and overcame when the pulsar observations with VLBI are carded out. As lots of progress have been made in the field of pulsar observation with VLBI and data reduction, more and more VLBI networks take part in pulsar research and many good results have been achieved. The possibility of successful VLBI observation can be enhanced by the technique taking pulsar signals out in the correlation process, which can boot the signal to noise ratio of the observation. There is a very popular open source Distributed FX-style Software Correlator-DiFX, which is turned out to be very efficient and flexible. It has an incoherent de-dispersion module and advanced Pulsar Binning module. So it behaves very well in the correlation of VLBI observation data of pulsars. DiFX have been successfully installed on our single desktop computer. The process of installing, debugging running DiFX and the recent progress of correlating the VLBI pulsar observation data are introduced in this paper. The first time observation data （the target is PSR B0329＋54） with Chinese VLBI networks （CVN） is correlated with DiFX installed on our desktop computer under the normal mode and the pulsar binning mode. By comparison, Pulsar Binning can boot the signal to noise ratio significantly. Furthermore, the correlation of our EVN observations of PSR J1022＋1001, whose flux is as weak as 2.6 mJy and the period is as short as 16 ms, is done with the Bonn-DiFX on the computer cluster at the Max-Planck Institute for Radio Astronomy （MPIfR）. Finally, the problems we are facing in the process of correlating pulsar VLBI observation data with DiFX are discussed. Prospects of the pulsar research with CVN are also given in the end of this paper.