pygedm.ne2001_wrapper

Python wrapper for NE2001 model code.

References

[1] 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.

[2] 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.

pygedm.ne2001_wrapper.TAUISS(d, sm, nu)

Convert a scattering measure (SM) to scattering timescale at given frequency.

Direct port from FORTRAN code scattering98.f

Parameters:

• d (float) – Distance in kpc

• sm (float) – Scattering measure (kpc m^{-20/3})

• nu (float) – Radio frequency in GHz

Returns:

pulse broadening time (ms)

Return type:

tauiss (float)

Fortran equiv:

      REAL FUNCTION TAUISS(d, sm, nu)
c
c calculates the pulse broadening time in ms
c from distance, scattering measure, and radio frequency
c
c input:      d = pulsar distance       (kpc)
c            sm = scattering measure    (kpc m^{-20/3})
c            nu = radio frequency       (GHz)
c output: tausis = pulse broadening time (ms)
c
      implicit none
      real d, sm,  nu
      tauiss = 1000. * (sm / 292.)**1.2 * d * nu**(-4.4)
      end

pygedm.ne2001_wrapper.TRANSITION_FREQUENCY(d_eff: float, sm: float, xi: float = None) → float

The transition frequency between weak and strong scattering

Python implementation of Equation 17 in C&L 2002 [1].

Computes nu = (318 GHz) * xi^(10/17) * sm^(6/17) * d_eff^(5/17)

Parameters:

• d_eff (float) – effective distance to the scattering medium (kpc)

• sm (float) – Scattering measure (kpc m^{-20/3})

• xi (float) – Fresnel scale scaling factor (~1). If not supplied, sqrt(2 pi) is used as preferred definition.

Returns:

Transition frequency in GHz

Return type:

nu (float)

pygedm.ne2001_wrapper.calculate_electron_density_xyz(x, y, z)

Compute electron density at Galactocentric X, Y, Z coordinates

x,y,z are Galactocentric Cartesian coordinates, measured in kpc (NOT pc!) with the axes parallel to (l, b) = (90, 0), (180, 0), and (0, 90) degrees

Parameters:

• x (float) – Galactocentric coordinates in kpc

• y (float) – Galactocentric coordinates in kpc

• z (float) – Galactocentric coordinates in kpc

Returns:

Electron density in cm-3

Return type:

ne_out (astropy.Quantity)

pygedm.ne2001_wrapper.dist_to_dm(l, b, dist, nu=1.0, full_output=False)

Convert distance to DM and compute scattering timescale

Parameters:

• l (float) – galactic longitude in degrees

• b (float) – galactic latitude in degrees

• dist (float) – Distance in kpc

• nu (float in GHz or astropy.Quantity) – observing frequency (GHz)

• full_output (bool) – Return full raw output (dict) from NE2001 if set to True

Returns:

Dispersion measure (pc / cm3), scattering timescale at 1 GHz (s)

Return type:

dm (astropy.Quantity), tau_sc (astropy.Quantity)

pygedm.ne2001_wrapper.dm_to_dist(l, b, dm, nu=1.0, full_output=False)

Convert DM to distance and compute scattering timescale

Parameters:

• l (float) – galactic longitude in degrees

• b (float) – galactic latitude in degrees

• dm (floa) – Dispersion measure

• nu (float in GHz or astropy.Quantity) – observing frequency (GHz)

• full_output (bool) – Return full raw output (dict) from NE2001 if set to True

Returns:

Distance (pc), scattering timescale at 1 GHz (s)

Return type:

dist (astropy.Quantity), tau_sc (astropy.Quantity)

pygedm.ne2001_wrapper.run_from_pkgdir(f)

Decorator function to chdir() into package directory when running

NE2001 code doesn’t know the relative path to its data files. This wraps the function call, changing into the right directory first, calling it, then changing back to original directory.