A Linear Decomposition Method to Analyze and Study Pulsar Mode Changes

In this paper, we present the linear decomposition method (LDM), which we developed to detect and analyze pulsar profile variations and mode-changing behavior. We developed LDM utilizing the likelihood function approach assuming the Gaussian noise. The LDM projects pulse profiles onto significance-ordered orthonormal vector bases. We show that the method is similar to the principal component analysis, but the LDM can handle more general situations. We use a simulated data set and data from the Kunming 40 m radio telescope to demonstrate the application of the LDM. We found that the LDM successfully identified mode changes for well-known mode-changing PSR B0329+54 and found a continuous pulse profile evolution for PSR B0355+54. We also show that the LDM can be used to improve the timing precision for mode-changing PSR B0329+54.