1.5 The Observational Features
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or the spacecrafts carrying X-ray detection devices, X-ray pulsars can be observed in
outer space for a long time. Apparently, cost of observing the X-ray pulsars relative
to the radio ones is high. With X-ray pulsar-based navigation (XPNAV) technology
developing, more and more dedicated X-ray pulsar observation satellites will be
launched, and a large amount of X-ray data from the pulsars obtained and used to
build the database for the XPNAV.
The pulse profiles of the pulsars in the radio, visible, X-ray and gamma-ray bands
are different from one another and some pulsars have periodic pulse radiations only
in individual spectral bands. For example, The pulse profiles of the Crab Pulsar (PSR
B0531+21) and Vela Pulsar (PSR B0833–45) have been observed in the radio, visible,
X-ray and gamma-ray bands, but the shapes of pulse profiles have discrepancies in
the deferent frequency bands for each pulsar. In addition, the pulse profiles of PSR
B1909–58 and PSR B1055–52 have been observed in the radio, X-ray and gammaray bands, those of PSR B0633+17 (the Geminga Pulsar) in the visible, X-ray and
gamma-ray bands, and those of PSR B1706–44 and PSR B1951+32 in the radio and
gamma-ray bands. The X-ray and gamma-ray signals emitted from the Geminga are
first observed respectively by the High Energy Astrophysics Observatory-2 (HEAO2, also referred to as Einstein Observatory) and German X-ray astronomy satellite
ROSAT (short for Röntgensatellit). And then, the optical counterpart of the Geminga
is also discovered, and the Geminga is a blue spectrum star with the luminosity of
25.5 magnitudes.
Because there are discrepancies of the spatial dispersions of electromagnetic wave
signals from different frequency bands, their radiation mechanisms are also different.
For the pulse radiation with different energies, it is also possible that there is a
special radiation cone on the surface of pulsar, and thus there are discrepancies of
the pulse profiles among different frequency bands. Although the pulse profiles in
different frequency bands have discrepancies, their pulse periods are same for a
pulsar. It has been well known that the signals from pulsars are produced with their
rotations. The radiation cones in whatever shapes or with different locations, all will
sweep through detection devices with the pulsars rotating. So, the pulse periods from
different frequency bands should be same. Moreover, there is the phase difference
between the pulse profiles in the radio and X-ray bands. If the phase difference
between both can be determined accurately, the relation between the pulse profiles
in the two frequency bands is established definitely, and the timing models from the
X-ray pulsars will be made more accurately by using the radio observation data. And
thus, a pulsar-time reference system based on space-ground integration will be built.
1.5.2 Periodic Features
Pulsars are highly rapid rotation neutron stars, and their periodic ranges are typically
1.4 ms−8.5 s, while the periods of a few of pulsars get to tens of seconds. Generally,
the periodic change rates of most pulsars are positive, and thus it is shown that the
rotating velocities of the pulsars have been slowing down gradually. The periodic
31
or the spacecrafts carrying X-ray detection devices, X-ray pulsars can be observed in
outer space for a long time. Apparently, cost of observing the X-ray pulsars relative
to the radio ones is high. With X-ray pulsar-based navigation (XPNAV) technology
developing, more and more dedicated X-ray pulsar observation satellites will be
launched, and a large amount of X-ray data from the pulsars obtained and used to
build the database for the XPNAV.
The pulse profiles of the pulsars in the radio, visible, X-ray and gamma-ray bands
are different from one another and some pulsars have periodic pulse radiations only
in individual spectral bands. For example, The pulse profiles of the Crab Pulsar (PSR
B0531+21) and Vela Pulsar (PSR B0833–45) have been observed in the radio, visible,
X-ray and gamma-ray bands, but the shapes of pulse profiles have discrepancies in
the deferent frequency bands for each pulsar. In addition, the pulse profiles of PSR
B1909–58 and PSR B1055–52 have been observed in the radio, X-ray and gammaray bands, those of PSR B0633+17 (the Geminga Pulsar) in the visible, X-ray and
gamma-ray bands, and those of PSR B1706–44 and PSR B1951+32 in the radio and
gamma-ray bands. The X-ray and gamma-ray signals emitted from the Geminga are
first observed respectively by the High Energy Astrophysics Observatory-2 (HEAO2, also referred to as Einstein Observatory) and German X-ray astronomy satellite
ROSAT (short for Röntgensatellit). And then, the optical counterpart of the Geminga
is also discovered, and the Geminga is a blue spectrum star with the luminosity of
25.5 magnitudes.
Because there are discrepancies of the spatial dispersions of electromagnetic wave
signals from different frequency bands, their radiation mechanisms are also different.
For the pulse radiation with different energies, it is also possible that there is a
special radiation cone on the surface of pulsar, and thus there are discrepancies of
the pulse profiles among different frequency bands. Although the pulse profiles in
different frequency bands have discrepancies, their pulse periods are same for a
pulsar. It has been well known that the signals from pulsars are produced with their
rotations. The radiation cones in whatever shapes or with different locations, all will
sweep through detection devices with the pulsars rotating. So, the pulse periods from
different frequency bands should be same. Moreover, there is the phase difference
between the pulse profiles in the radio and X-ray bands. If the phase difference
between both can be determined accurately, the relation between the pulse profiles
in the two frequency bands is established definitely, and the timing models from the
X-ray pulsars will be made more accurately by using the radio observation data. And
thus, a pulsar-time reference system based on space-ground integration will be built.
1.5.2 Periodic Features
Pulsars are highly rapid rotation neutron stars, and their periodic ranges are typically
1.4 ms−8.5 s, while the periods of a few of pulsars get to tens of seconds. Generally,
the periodic change rates of most pulsars are positive, and thus it is shown that the
rotating velocities of the pulsars have been slowing down gradually. The periodic