THE CORRELATION BETWEEN DISPERSION MEASURE AND X-RAY COLUMN DENSITY FROM RADIO PULSARS

Pulsars are remarkable objects that emit across the entire electromagnetic spectrum, providing a powerful probe of the interstellar medium. In this study, we investigate the relation between dispersion measure (DM) and X-ray absorption column density NH using 68 radio pulsars detected at X-ray energies with the Chandra X-Ray Observatory or XMM-Newton. We find a best-fit empirical linear relation of , which corresponds to an average ionization of %, confirming the ratio of one free electron per 10 neutral hydrogen atoms commonly assumed in the literature. We also compare different NH estimates and note that some NH values obtained from X-ray observations are higher than the total Galactic H i column density along the same line of sight, while the optical extinction generally gives the best NH predictions.

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