A reexamination of the distribution of galactic free electrons.
GOMEZ G.C., BENJAMIN R.A. and COX D.P.
Abstract (from CDS):
We present a list of 109 pulsars with independent distance information compiled from the literature. Since the compilation of Frail & Weisberg, there are 35 pulsars with new distance estimates and 25 pulsars for which the distance or distance uncertainty have been revised. We used this data to fit a smooth, axisymmetric, two-disk model of the distribution of Galactic electrons. The two exponential model components have mean local midplane densities at the solar circle of 2.03x10–2 and 0.71x10–2 cm–3, and scale heights of 1.07 and 0.053 kpc. The thick component shows very little radial variation, while the second has a radial scale length of only a few kiloparsecs. We also examined a model that varies as sech2x, rather than exp(-x), in both the radial and vertical directions. We prefer this model with no midplane cusp but find that the fit parameters essentially describe the same electron distribution. The distances predicted by this distribution have a similar scatter to that produced by the more complex model of Taylor & Cordes. We examine the pulsars that deviate strongly from this model. There are two regions of enhanced dispersion measure, one of which correlates well with the Sagittarius-Carina spiral arm. We find that the scatter of the observed dispersion measure from the model is not fitted well by either a normal or a lognormal distribution of lump sizes but may be caused instead by the uncertainties in the distances.
Galaxies: ISM - Galaxy: Structure - ISM: H II Regions - ISM: General - Stars: Pulsars: General
Notes: 1740-53 = PSR J1740-5340, 1807-24 = PSR J1807-2459, 1910-59 = PSR J1910-59, 1701-30 = PSR J1701-3006