# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""Simple models for cosmic ray spectra at Earth.
For measurements, the "Database of Charged Cosmic Rays (CRDB)" is a great resource:
http://lpsc.in2p3.fr/cosmic-rays-db/
"""
import numpy as np
from astropy import units as u
from gammapy.modeling import Parameter
from .spectral import PowerLawSpectralModel, SpectralModel
__all__ = [
"create_cosmic_ray_spectral_model",
]
class _LogGaussianSpectralModel(SpectralModel):
r"""Log Gaussian spectral model with a weird parametrisation.
This should not be exposed to end-users as a Gammapy spectral model!
See Table 3 in https://ui.adsabs.harvard.edu/abs/2013APh....43..171B
"""
L = Parameter("L", 1e-12 * u.Unit("cm-2 s-1"))
Ep = Parameter("Ep", 0.107 * u.TeV)
w = Parameter("w", 0.776)
@staticmethod
def evaluate(energy, L, Ep, w):
return (
L
/ (energy * w * np.sqrt(2 * np.pi))
* np.exp(-((np.log(energy / Ep)) ** 2) / (2 * w**2))
)
[docs]def create_cosmic_ray_spectral_model(particle="proton"):
"""Cosmic a cosmic ray spectral model at Earth.
These are the spectra assumed in this CTA study:
Table 3 in https://ui.adsabs.harvard.edu/abs/2013APh....43..171B
The spectrum given is a differential flux ``dnde`` in units of
``cm-2 s-1 TeV-1``, as the value integrated over the whole sky.
To get a surface brightness you need to compute
``dnde / (4 * np.pi * u.sr)``.
To get the ``dnde`` in a region of solid angle ``omega``, you need
to compute ``dnde * omega / (4 * np.pi * u.sr)``.
The hadronic spectra are simple power-laws, the electron spectrum
is the sum of a power law and a log-normal component to model the
"Fermi shoulder".
Parameters
----------
particle : {'electron', 'proton', 'He', 'N', 'Si', 'Fe'}
Particle type
Returns
-------
`~gammapy.modeling.models.SpectralModel`
Spectral model (for all-sky cosmic ray flux)
"""
omega = 4 * np.pi * u.sr
if particle == "proton":
return PowerLawSpectralModel(
amplitude=0.096 * u.Unit("1 / (m2 s TeV sr)") * omega,
index=2.70,
reference=1 * u.TeV,
)
elif particle == "N":
return PowerLawSpectralModel(
amplitude=0.0719 * u.Unit("1 / (m2 s TeV sr)") * omega,
index=2.64,
reference=1 * u.TeV,
)
elif particle == "Si":
return PowerLawSpectralModel(
amplitude=0.0284 * u.Unit("1 / (m2 s TeV sr)") * omega,
index=2.66,
reference=1 * u.TeV,
)
elif particle == "Fe":
return PowerLawSpectralModel(
amplitude=0.0134 * u.Unit("1 / (m2 s TeV sr)") * omega,
index=2.63,
reference=1 * u.TeV,
)
elif particle == "electron":
return PowerLawSpectralModel(
amplitude=6.85e-5 * u.Unit("1 / (m2 s TeV sr)") * omega,
index=3.21,
reference=1 * u.TeV,
) + _LogGaussianSpectralModel(L=3.19e-3 * u.Unit("1 / (m2 s sr)") * omega)
else:
raise ValueError(f"Invalid particle: {particle!r}")