Time evolution of X-ray jet’s velocity
An X-ray jet is a kind of flares in the Sun. The model of X-ray jets based on magnetic reconnection (Shibata et al. 1992) predicts that two flows with the different velocities are included in one X-ray jet. The velocity of one flow roughly equals to Alfven velocity (~1000 km/s), and the flow is accelerated by the magnetic force. The other one is
accelerated by the pressure gradient and its velocity is similar to the sound velocity (~200 km/s). However, the observational results (e.g. Shimojo et al. 2000) before the Hinode era show that the velocities of most X-ray jets are slower than the sound velocity.
Because the X-ray telescope (XRT) aboard the Hinode satellite has capability to observe the corona with the high temporal (< 1 min) and high spatial (~ 1 arcsec) resolutions, the XRT data revealed that an X-ray jet includes two components with the different velocities (Cirtain et al. 2007). The properties of the components have some differences from the model. For example, the components are not observed simultaneously. One component with sound velocity continues to appear until the peak time of the X-ray jet. The other one with Alfven velocity appear transiently. There is only one report using four X-ray jets by Cirtain et al. (2007) and their result does not show the time evolution of the velocity in X-ray jets, yet. In order to reveal the evolution of the X-ray jet's velocity, and investigate how the high velocity component occurs transiently in an X-ray jet, we detected 13 polar X-ray jets from the coronal data observed with XRT and investigated the time evolution of the velocity of the X-ray jets. The result shows that it is common that an X-ray jet includes the plural components with the different velocities. However, we could detect component with Alfven velocity in only three of the 13 events. In the talk, I introduce our data analysis and show the details of our result.