The pulse period (about 7.6 s) and change rate of the pulse period (about -2.6 x 10-11 s/s) of the X-ray Binary Pulsar 4U1626-67 are obtained with MAXI/GSC data.
The pulse period (red points in the figure, plotted in frequency) was obtained in each 60-day MAXI/GSC data from MJD 55110 up to 56249. The results were superposed with those with Fermi/GBM (black points). MAXI data are consistent with the Fermi/GBM data. Each red bar with the red point represents an average change-rate of the pulse period with MAXI in the 60 days. The pulse period is getting shorter and shorter (= spinning up) with alomost a constant change rate.
The next figure shows residuals from a linear fit to the Fermi/GBM data. Red points and black points represent MAXI and Fermi/GBM data, respectively. The vertical axis is in frequency. MAXI data points have an error bar, but it is small enough as is sometimes included in the size of the red points. The data is V-shaped, and there is a break in the middle. We found that the flux after this point was brighter than that before. We interprete that amount of gas accreting to the neutron star increased at this point to cause an increase in the spin-up rate.