The YMW16 electron-density model
YMW16 is a model for the distribution of free electrons in the Galaxy (Gal), the Magellanic Clouds (MC) and the inter-galactic medium (IGM) that can be used to estimate distances for real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure.
The Galactic model is based on 189 pulsars which have independently determined distances as well as dispersion measures, whereas simpler models are used for the electron density in the MC and the IGM. It is estimated that the 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. Pulse broadening due to scattering in the Galactic interstellar medium, the Magellanic Clouds, the intergalactic medium and FRB host galaxies is estimated.
As well as the ymw16 dm-distance program, we also provide a program, ymw16_ne, which gives the electron density at any point in the Galaxy or the Magellanic Clouds.
A paper by Yao, Manchester and Wang giving a complete description of the model and comparing its predictions with those of earlier Galactic electron density models is published in Astrophysical Journal, vol. 835, eid 29 (2017) and is also available on arXiv (1610.09448v2). YMW16 is the first electron-density model to estimate extragalactic pulsar distances and FRB distances.
Electron Density Program
Entries marked with a * are required.
(x, y, z): Galactocentric coordinate system with x-axis parallel to gl=90 deg., y-axis parallel to gl=180 deg., and z-axis towards the NGP.(gl, gb, dist): Galactic longtitude (0 to 360), Galactic latitude (-90 to 90), and distance (in pc).ncrd: For ncrd=1, the input is (x, y, z). For ncrd=2, the input is (gl, gb, dist).The output electron density has units of cm^-3.Distance-Dispersion Measure Program
Entries marked with a * are required.
DM or Dist: One of DM (cm^−3 pc) or distance, depending on ndir. Distance has units of pc for modes Gal and MC and Mpc for mode IGM.DM Host: Optional dispersion measure of host galaxy (default 100 cm^−3 pc). (Note: if present, DM Host is ignored for Gal and MC modes.)ndir: ndir=1 converts from DM to Dist and ndir=2 converts from distance to DM. The output tau_sc has units of seconds.