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Python/C++ version of YMW16 electron density model

Project description

Build Status License: LGPL v3 Coverage Status


Python bindings for the YMW16, NE2001 and YT2020 electron density models

This package is a Python interface to the YMW16 and NE2001 electron density models, and YT2020 halo model. The Yao, Manchester and Wang (2017, Astrophys. J., 835, 29; arXiv:1610.09448) YMW16 electron density model, is written in C++, and the Cordes and Lazio (2001, arXiv:0207156) NE2001 model is written in FORTRAN. This package, PyGEDM, wraps these two codes using pybind11 and f2py.


Some usage examples can be found in the examples directory.

import pygedm

# calculate DM at a given distance
DM, tau_sc = pygedm.dist_to_dm(204.0, -6.5, 200, method='ne2001')
DM, tau_sc = pygedm.dist_to_dm(204.0, -6.5, 200, method='ymw16')

# calculate distance for a given sky position and DM
dist, tau_sc = pygedm.dm_to_dist(123.4, 4.0, 200)

# calculate N_e density at xyz galactocentric coordinates
ne = pygedm.calculate_electron_density_xyz(1.0, 2.0, 3.0)

# calculate N_e density at Galactic lat/long/distance coords
ne = pygedm.calculate_electron_density_lbr(204.0, -6.5, 3000.0)

# Calculate halo DM contribution
dm_halo = pygedm.calculate_halo_dm(gl=0, gb=30)

The methods return astropy Quantities, which have units attached, and can accept astropy Angles and Quantities as arguments:

import pygedm
import astropy.units as u
import astropy.coordinates as c
DM = u.Quantity(10.0, unit='pc cm^-3')
ra, dec = c.Angle(23.0, unit='hourangle'), c.Angle('-43:00:02', unit='degree')
sky_coords = c.SkyCoord(ra, dec, frame='icrs')
dist, tau_sc = pygedm.dm_to_dist(sky_coords.galactic.l, sky_coords.galactic.b, DM)

>> 3362.16343117 lyr
>> 7.758686138 ns


Requires pybind11, astropy, and a newish C compiler with C++11 support (Ubuntu 16.04+ default gcc will work), plus a fortran compiler (generally gfortran).

You should be able to install with:

pip install git+

Or, download this repository and install via

python install

To run unit tests, run python test. Note that these tests only check the Python bindings, not the underlying C/FORTRAN source code (which is not supplied with unit tests).


If using PyGEDM in a journal article, please remember to cite the underlying electron density models:

Cordes, J. M., & Lazio, T. J. W. (2002),
NE2001.I. A New Model for the Galactic Distribution of Free Electrons and its Fluctuations, arXiv e-prints, astro-ph/0207156.

Cordes, J. M., & Lazio, T. J. W. (2003),
NE2001. II. Using Radio Propagation Data to Construct a Model for the Galactic Distribution of Free Electrons, arXiv e-prints, astro-ph/0301598.

Yao, J. M., Manchester, R. N., & Wang, N. (2017),
A New Electron-density Model for Estimation of Pulsar and FRB Distances, ApJ, 835, 29.

Yamasaki, S., & Totani, T. (2019),
The Galactic Halo Contribution to the Dispersion Measure of Extragalactic Fast Radio Bursts, arXiv e-prints, arXiv:1909.00849.

These are available in bibtex format in references.bib, and also as an ADS library.


YMW16 is a model for the distribution of free electrons in the Galaxy, the Magellanic Clouds and the inter-galactic medium, that can be used to estimate distances for real or simulated pulsars and fast radio bursts (FRBs) based on their position and dispersion measure.

The Galactic model is based on 189 pulsars that 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 Magellanic Clouds.

A paper (Yao, Manchester and Wang, 2017, Astrophys. J., 835, 29; arXiv:1610.09448) describes the model and compares its predictions with those of earlier Galactic electron density models. YMW16 is the first electron-density model to estimate extragalactic pulsar distances and FRB distances.

To make a command-line executable version of the program, download and unpack the latest version of the program. Then run "make_ymw16" to create the executable. The environment variable YMW16_DIR may be set up to point at a directory containing ymw16par.txt and spiral.txt. Access to these files is needed at runtime.

Websites allowing interactive access to the YMW16 distance model and download of the latest program version are available at:

Please report any issues or bugs at or directly to the authors. Please provide an example illustrating the problem.


Copyright (C) 2016, 2017  J. M. Yao, R. N. Manchester, N. Wang.

YMW16 is free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at your
option) any later version.

YMW16 is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
available at, for more details.

Jumei Yao (yaojumei _@_, Richard N Manchester
(dick.manchester _@_, Na Wang ( _@_


07 July 2002 To compile and execute the code, see code.pdf.

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