1.5 The Observational Features
37
In general, the polarization is divided into linear polarization and circular polarization. The former is that all electric vectors are parallel one other and their direction
constant. The latter is that the directions of all electric vectors will be rotated with the
radiation frequencies. The radiations of many radio pulsars have very strong linear
polarizations, whose strengths are far higher than the circular polarizations. In some
cases, the linear polarization rates even get to 100 percent for the radio pulsars. It
is a key feature for the synchrotron and curvature radiation mechanisms of pulsars.
By utilizing the polarizations of the radiations from pulsars, the interstellar magnetic
field strengths can be determined.
The signals radiated from pulsars have traveled through a very long distance before
they arrive at the observers, and carry the interstellar medium with weak magnetic
fields. And thus, the polarization plane will bring up the Faraday rotation, which
is that when the electromagnetic waves of the linear polarization cross through the
electromagnetic fields, a rotation of the polarization planes relative to the incident
waves will be produced under the action of the electromagnetic fields. The Faraday
rotation is a magneto-optical phenomenon, discovered by a British physicist Michael
Faraday (1791−1867) in 1845, and also called Faraday effects.
The rotational angle of the polarization plane is associated with the wavelength of
electromagnetic wave, electron density, length of the propagation path and interstellar
magnetic field strength, and can approximately be expressed as
α = 0.81λ
2 n e L B p ,
(1.13)
where α is the rotation angle of polarization plane (at a unit of radians), λ is the
wavelength of electromagnetic wave (at a unit of meter), n e is the electron density
(at a unit of the electron counts per cubic centimeter), L is the distance of pulsar (at
a unit of parsec), and B p is the component of the interstellar magnetic field strength
parallel to the line-of-sight (at a unit of micro Gauss).
Supposed that L and n e are known, B p can be calculated by using formula
(1.13), comparing two rotational angles (α) obtained from different wavelengths.
And thereby, the interstellar magnetic field strengths with an order of micro Gauss
can be obtained by using the method to process the observational data from pulsars.
Of course, it is also so far the most effective method to measure the interstellar
magnetic field strength. Therefore, an important approach to studying the interstellar
medium characteristics is provided by observing pulsars.
1.5.6 Spatial Motion
For the observers on the Earth, all observed pulsars are moving relative to the Earth.
By correcting the revolution of the Earth around the Sun and its self rotation, the
movements of the pulsars relative to the Solar System’s Barycenter (SSB) can be
37
In general, the polarization is divided into linear polarization and circular polarization. The former is that all electric vectors are parallel one other and their direction
constant. The latter is that the directions of all electric vectors will be rotated with the
radiation frequencies. The radiations of many radio pulsars have very strong linear
polarizations, whose strengths are far higher than the circular polarizations. In some
cases, the linear polarization rates even get to 100 percent for the radio pulsars. It
is a key feature for the synchrotron and curvature radiation mechanisms of pulsars.
By utilizing the polarizations of the radiations from pulsars, the interstellar magnetic
field strengths can be determined.
The signals radiated from pulsars have traveled through a very long distance before
they arrive at the observers, and carry the interstellar medium with weak magnetic
fields. And thus, the polarization plane will bring up the Faraday rotation, which
is that when the electromagnetic waves of the linear polarization cross through the
electromagnetic fields, a rotation of the polarization planes relative to the incident
waves will be produced under the action of the electromagnetic fields. The Faraday
rotation is a magneto-optical phenomenon, discovered by a British physicist Michael
Faraday (1791−1867) in 1845, and also called Faraday effects.
The rotational angle of the polarization plane is associated with the wavelength of
electromagnetic wave, electron density, length of the propagation path and interstellar
magnetic field strength, and can approximately be expressed as
α = 0.81λ
2 n e L B p ,
(1.13)
where α is the rotation angle of polarization plane (at a unit of radians), λ is the
wavelength of electromagnetic wave (at a unit of meter), n e is the electron density
(at a unit of the electron counts per cubic centimeter), L is the distance of pulsar (at
a unit of parsec), and B p is the component of the interstellar magnetic field strength
parallel to the line-of-sight (at a unit of micro Gauss).
Supposed that L and n e are known, B p can be calculated by using formula
(1.13), comparing two rotational angles (α) obtained from different wavelengths.
And thereby, the interstellar magnetic field strengths with an order of micro Gauss
can be obtained by using the method to process the observational data from pulsars.
Of course, it is also so far the most effective method to measure the interstellar
magnetic field strength. Therefore, an important approach to studying the interstellar
medium characteristics is provided by observing pulsars.
1.5.6 Spatial Motion
For the observers on the Earth, all observed pulsars are moving relative to the Earth.
By correcting the revolution of the Earth around the Sun and its self rotation, the
movements of the pulsars relative to the Solar System’s Barycenter (SSB) can be