NE2001: A New Model for the Galactic Electron Density and its Fluctuations

摘要

A new model is presented for the Galactic distribution of free electrons based on work by J. Lazio and J. Cordes. It (a) describes the distribution of electrons responsible for pulsar dispersion measures and thus provides a distance scale for pulsars; (b) describes the distribution of electron density microstructure that underlies interstellar scattering; (c) can be used to interpret interstellar scattering and scintillation observations of Galactic objects and of extragalactic objects (compact AGNs and Gamma-ray burst afterglows); and (d) serves as a preliminary, smooth spatial model of the warm ionized component of the interstellar gas. This work builds upon and supersedes the Taylor & Cordes (1993) model by exploiting new observations and methods, including (1) a near doubling of the number of dispersion and scattering measurements; (2) better independent distance measurements; (3) improved measurements of scattering toward the Galactic center; (4) improved constraints on the (Galactocentric) radial distribution of free electrons; (5) redefinition of the Galaxy's spiral arms; (6) modeling of the local interstellar medium, including the local hot bubble identified by X-ray and NaI absorption measurements; and (7) an improved likelihood analysis for constraining the model parameters. Future observations and analysis techniques that will improve the Galactic model will be discussed, including deep pulsar surveys with Arecibo, VLBI on large samples of AGNs, and very deep surveys with the Square Kilometer Array. Constraints on the role of turbulence are expected through a combination of low-frequency radio astronomy with LOFAR and gamma-ray observations with GLAST.