One problem with psrtime is that although it can be used to fit up to three exponentials to the residuals there is no facility to apply the effects of many glitches progressively to the data. To overcome this problem, a program called vfit was written. This has a gui as other programs and is used to plot frequency against time for a pulsar. The starting point is that it can be given the normal slow down parameters of epoch, frequency and the next three time derivatives of frequency. There is also allowed any number of glitches where the glitch parameters are epoch, delta period and delta vdot, and delta vddot, together with three eponentials each comprising an amplitude and time constant. The quantities can be fitted to for each glitch. The frequency data can be in either frequency or period format, the necessary transmortion taking place within the program.
Start and stop times can be set for the range of the fit, together with the expected zoom and unzoom facilities. Hardcopies can be sent to postscript file, and the parameters can be saved as well as the residuals being written to a file.
Although the normal slow down parameters are always shown, the user
has to select which glitch parameters will be displayed.
