Multi-component sources

A multi-component source is a point source (or extended source) which has different spectral components. For example, in a Gamma-Ray Bursts you can have a Synchrotron component and an Inverse Compton component, which come from different zones and are described by different spectra. Depending on the needs of your analysis, you might model this situation using a single component constituted by the sum of the two spectra, or you might want to model them independently. Each component has its own polarization, which can be useful when studying polarized sources (to be implemented). The latter choice allows you to measure for instance the fluxes from the two components independently. See below for an example of how to create a source with two named spectral components (of course, the spectral shapes can be arbitrary).

Sources with multiple *spatial* components are not currently supported. As a workaround, you can create two functions with the same spectral shape and link any relevant parameters. There is no restriction against overlapping extended sources.

from astromodels import *
component1 = SpectralComponent('synchrotron',shape=Powerlaw())
component2 = SpectralComponent('IC',shape=Powerlaw())
multicomp_source = PointSource('multicomp_source', ra=123.2, dec=-13.2, components=[component1,component2])

multicomp_source.display()

[WARNING ] The naima package is not available. Models that depend on it will not be available
[WARNING ] The GSL library or the pygsl wrapper cannot be loaded. Models that depend on it will not be available.
_setup
_setup
index
piv
K
index
piv
K
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• multicomp_source (point source):
  • position:
    • ra:
      • value: 123.2
      • desc: Right Ascension
      • min_value: 0.0
      • max_value: 360.0
      • unit: deg
      • is_normalization: False
    • dec:
      • value: -13.2
      • desc: Declination
      • min_value: -90.0
      • max_value: 90.0
      • unit: deg
      • is_normalization: False
    • equinox: J2000
  • spectrum:
    • synchrotron:
      • Powerlaw:
        • K:
          • value: 1.0
          • desc: Normalization (differential flux at the pivot value)
          • min_value: 1e-30
          • max_value: 1000.0
          • unit: keV-1 s-1 cm-2
          • is_normalization: True
        • piv:
          • value: 1.0
          • desc: Pivot value
          • min_value: None
          • max_value: None
          • unit: keV
          • is_normalization: False
        • index:
          • value: -2.01
          • desc: Photon index
          • min_value: -10.0
          • max_value: 10.0
          • unit:
          • is_normalization: False
    • IC:
      • Powerlaw:
        • K:
          • value: 1.0
          • desc: Normalization (differential flux at the pivot value)
          • min_value: 1e-30
          • max_value: 1000.0
          • unit: keV-1 s-1 cm-2
          • is_normalization: True
        • piv:
          • value: 1.0
          • desc: Pivot value
          • min_value: None
          • max_value: None
          • unit: keV
          • is_normalization: False
        • index:
          • value: -2.01
          • desc: Photon index
          • min_value: -10.0
          • max_value: 10.0
          • unit:
          • is_normalization: False

Modifying features of the source and modify parameters of its spectrum

Starting from the source instance you can modify any of its components, or its position, in a straightforward way.

Changing position:

multicomp_source.position.ra = 124.5
multicomp_source.position.dec = -11.5

position
position

Change values for the parameters:

multicomp_source.spectrum.synchrotron.shape.K = 1e-2
multicomp_source.spectrum.IC.shape.index = -1.0
multicomp_source.display()

spectrum
synchrotron
spectrum
IC
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• multicomp_source (point source):
  • position:
    • ra:
      • value: 124.5
      • desc: Right Ascension
      • min_value: 0.0
      • max_value: 360.0
      • unit: deg
      • is_normalization: False
    • dec:
      • value: -11.5
      • desc: Declination
      • min_value: -90.0
      • max_value: 90.0
      • unit: deg
      • is_normalization: False
    • equinox: J2000
  • spectrum:
    • synchrotron:
      • Powerlaw:
        • K:
          • value: 0.01
          • desc: Normalization (differential flux at the pivot value)
          • min_value: 1e-30
          • max_value: 1000.0
          • unit: keV-1 s-1 cm-2
          • is_normalization: True
        • piv:
          • value: 1.0
          • desc: Pivot value
          • min_value: None
          • max_value: None
          • unit: keV
          • is_normalization: False
        • index:
          • value: -2.01
          • desc: Photon index
          • min_value: -10.0
          • max_value: 10.0
          • unit:
          • is_normalization: False
    • IC:
      • Powerlaw:
        • K:
          • value: 1.0
          • desc: Normalization (differential flux at the pivot value)
          • min_value: 1e-30
          • max_value: 1000.0
          • unit: keV-1 s-1 cm-2
          • is_normalization: True
        • piv:
          • value: 1.0
          • desc: Pivot value
          • min_value: None
          • max_value: None
          • unit: keV
          • is_normalization: False
        • index:
          • value: -1.0
          • desc: Photon index
          • min_value: -10.0
          • max_value: 10.0
          • unit:
          • is_normalization: False

Spectral components can be assigned to python variables to modify several parameters without too much repetition:

po = multicomp_source.spectrum.synchrotron.shape
po.K = 0.1/u.keV/u.cm**2/u.s
po.K.min_value = 1e-10/u.keV/u.cm**2/u.s
multicomp_source.display()

spectrum
synchrotron
K
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• multicomp_source (point source):
  • position:
    • ra:
      • value: 124.5
      • desc: Right Ascension
      • min_value: 0.0
      • max_value: 360.0
      • unit: deg
      • is_normalization: False
    • dec:
      • value: -11.5
      • desc: Declination
      • min_value: -90.0
      • max_value: 90.0
      • unit: deg
      • is_normalization: False
    • equinox: J2000
  • spectrum:
    • synchrotron:
      • Powerlaw:
        • K:
          • value: 0.1
          • desc: Normalization (differential flux at the pivot value)
          • min_value: 1e-10
          • max_value: 1000.0
          • unit: keV-1 s-1 cm-2
          • is_normalization: True
        • piv:
          • value: 1.0
          • desc: Pivot value
          • min_value: None
          • max_value: None
          • unit: keV
          • is_normalization: False
        • index:
          • value: -2.01
          • desc: Photon index
          • min_value: -10.0
          • max_value: 10.0
          • unit:
          • is_normalization: False
    • IC:
      • Powerlaw:
        • K:
          • value: 1.0
          • desc: Normalization (differential flux at the pivot value)
          • min_value: 1e-30
          • max_value: 1000.0
          • unit: keV-1 s-1 cm-2
          • is_normalization: True
        • piv:
          • value: 1.0
          • desc: Pivot value
          • min_value: None
          • max_value: None
          • unit: keV
          • is_normalization: False
        • index:
          • value: -1.0
          • desc: Photon index
          • min_value: -10.0
          • max_value: 10.0
          • unit:
          • is_normalization: False

Be careful when creating a shortcut directly to a parameter.

p1 = multicomp_source.spectrum.synchrotron.shape.K
print (type(p1), p1)
p1 = 0.3
print (type(p1), p1)

spectrum
synchrotron
K
<class 'astromodels.core.parameter.Parameter'> Parameter K = 0.1 [1 / (cm2 keV s)]
(min_value = 1e-10, max_value = 1000.0, delta = 0.1, free = True)
<class 'float'> 0.3

This did not change the value of K, but instead assigned the float 0.3 to p1 (i.e., destroy the shortcut).

However you can change the value of p1 like this:

p1 = multicomp_source.spectrum.synchrotron.shape.K
p1.value = 0.5
multicomp_source.display()

spectrum
synchrotron
K
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• multicomp_source (point source):
  • position:
    • ra:
      • value: 124.5
      • desc: Right Ascension
      • min_value: 0.0
      • max_value: 360.0
      • unit: deg
      • is_normalization: False
    • dec:
      • value: -11.5
      • desc: Declination
      • min_value: -90.0
      • max_value: 90.0
      • unit: deg
      • is_normalization: False
    • equinox: J2000
  • spectrum:
    • synchrotron:
      • Powerlaw:
        • K:
          • value: 0.5
          • desc: Normalization (differential flux at the pivot value)
          • min_value: 1e-10
          • max_value: 1000.0
          • unit: keV-1 s-1 cm-2
          • is_normalization: True
        • piv:
          • value: 1.0
          • desc: Pivot value
          • min_value: None
          • max_value: None
          • unit: keV
          • is_normalization: False
        • index:
          • value: -2.01
          • desc: Photon index
          • min_value: -10.0
          • max_value: 10.0
          • unit:
          • is_normalization: False
    • IC:
      • Powerlaw:
        • K:
          • value: 1.0
          • desc: Normalization (differential flux at the pivot value)
          • min_value: 1e-30
          • max_value: 1000.0
          • unit: keV-1 s-1 cm-2
          • is_normalization: True
        • piv:
          • value: 1.0
          • desc: Pivot value
          • min_value: None
          • max_value: None
          • unit: keV
          • is_normalization: False
        • index:
          • value: -1.0
          • desc: Photon index
          • min_value: -10.0
          • max_value: 10.0
          • unit:
          • is_normalization: False