Getting Estimates for Pulsar Red Noise Using Allan Variance on NICER Data

Understanding the noise in pulsar timing arrays (PTAs) is an ever-growing research field. One of the best ways to understand frequency-dependent effects caused by the interstellar medium is to use high-energy photons, which are effectively impervious to path-dependent propagation effects as they travel to Earth. We can use X-ray data obtained by NICER to explore the possibility of mis-modeled chromatic noise across the MSP population. We can obtain the associated amplitude and spectral index values for the red noise (RN) using analysis techniques similar to radio data. Since X-ray data can be (effectively) evenly sampled across time, we can measure the Modified Allan Variance, a standard for atomic clock errors, by sampling different red noise and white noise combinations from the traditional techniques and creating different realizations of the NICER residuals. We determine the variance for each pulsar in our array. In this talk, I will compare the red noise spectral index and gamma results found with those of the traditional radio telescope and the Allan variance technique. I will also compare these results with the red noise seen by the various radio pulsar timing groups and discuss any chromatic effects we find to be evident in the analysis.