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5 X-ray Pulsar-Based Navigation: Theories and Experiments
5.8.2 Observations of Typical Pulsars and X-Ray Binary
Stars
According to the mission design requirements for the XPNAV-1 satellite, up to now,
we have carried out the observations for many celestial objects, such as the four
typical pulsars, the four X-ray binary stars, the center of the Galactic System and
the supernova remnants, as well as conducted the relevant scientific experiments.
Considering that the Crab pulsar has the highest X-ray photon radiation flux in the
RP pulsars and the effective detection area of the TSXS is only 30 cm
2 , hence the Crab
pulsar becomes the core observation target in the entire XPNAV-1 mission. When the
satellite passes through the South Atlantic Anomaly (SAA) area, the TSXS is always
shut down in order to avoid damage to detector performance caused by high flux and
high-energy particle radiation. When the satellite enters into the orbital arc-segment
of the Earth’s occlusion, no observation plan is arranged. In addition, when the angle
between the observation target and the Sun is less than 45°, or the angle between
the observation target and the Moon is less than 5°, the observation will be stopped
to avoid a large amount of high-energy particles entering the detector. As a result,
within an orbital period, there is only an observational arc-segment arranged, usually
with the duration of 30−50 min.
In order to process the observed data from the XPNAV-1, a dedicated data
processing software package has been developed under the actual X-ray data
processing mode of the ground test system. The software package contains eleven
software modules, which are responsible for original data unpacking, effective photon
identifying, photon counting, energy-spectrum analysis, orbit propagation, photon
arrival-time correction, pulsar database construction, pulse period searching, pulse
profile extraction, pulsar timing parameter estimation, and orbit and time parameter
determination, respectively [37]. By analyzing and processing the observation data,
the observation results have been obtained for the candidate objects, such as the Xray photon flux, energy-spectrum curve, photon arrival-time interval, pulse-period
feature, pulse profile, pulsar timing model and navigation parameter estimation.
On November 20, 2016, the first batch of observation data from the XPNAV-1
was obtained by detecting the X-ray photons from the Crab pulsar with the detector
TSXS, and composed of six observation arc-segments, with a total of 273 min. The
results of photon counting per second for the six observation arc-segments are shown
in Fig. 5.32. According to the effective detection area and detection efficiency of the
TSXS, the average X-ray photon flux of the Crab pulsar, statistically calculated by
using the first batch of observation data from the XPNAV-1, is 1.51 ph/cm
2 /s, while
the nominal value of X-ray photon flux of the Crab pulsar is 1.54 ph/cm
2 /s generally.
Apparently, both are almost same. Meanwhile, the energy-spectrum analysis results
of the Crab pulsar within the energy band of 0.5−10 keV are shown in Fig. 5.33,
where the horizontal axis is expressed with the common logarithm of energy. From
Fig. 5.33, it can be seen that the highest X-ray photon flux radiated by the Crab
pulsar occurs near the energy of 1 keV, and there is a peak value at energy of 10 keV,
resulting from cumulatively counting the high-energy particles with the energy of
5 X-ray Pulsar-Based Navigation: Theories and Experiments
5.8.2 Observations of Typical Pulsars and X-Ray Binary
Stars
According to the mission design requirements for the XPNAV-1 satellite, up to now,
we have carried out the observations for many celestial objects, such as the four
typical pulsars, the four X-ray binary stars, the center of the Galactic System and
the supernova remnants, as well as conducted the relevant scientific experiments.
Considering that the Crab pulsar has the highest X-ray photon radiation flux in the
RP pulsars and the effective detection area of the TSXS is only 30 cm
2 , hence the Crab
pulsar becomes the core observation target in the entire XPNAV-1 mission. When the
satellite passes through the South Atlantic Anomaly (SAA) area, the TSXS is always
shut down in order to avoid damage to detector performance caused by high flux and
high-energy particle radiation. When the satellite enters into the orbital arc-segment
of the Earth’s occlusion, no observation plan is arranged. In addition, when the angle
between the observation target and the Sun is less than 45°, or the angle between
the observation target and the Moon is less than 5°, the observation will be stopped
to avoid a large amount of high-energy particles entering the detector. As a result,
within an orbital period, there is only an observational arc-segment arranged, usually
with the duration of 30−50 min.
In order to process the observed data from the XPNAV-1, a dedicated data
processing software package has been developed under the actual X-ray data
processing mode of the ground test system. The software package contains eleven
software modules, which are responsible for original data unpacking, effective photon
identifying, photon counting, energy-spectrum analysis, orbit propagation, photon
arrival-time correction, pulsar database construction, pulse period searching, pulse
profile extraction, pulsar timing parameter estimation, and orbit and time parameter
determination, respectively [37]. By analyzing and processing the observation data,
the observation results have been obtained for the candidate objects, such as the Xray photon flux, energy-spectrum curve, photon arrival-time interval, pulse-period
feature, pulse profile, pulsar timing model and navigation parameter estimation.
On November 20, 2016, the first batch of observation data from the XPNAV-1
was obtained by detecting the X-ray photons from the Crab pulsar with the detector
TSXS, and composed of six observation arc-segments, with a total of 273 min. The
results of photon counting per second for the six observation arc-segments are shown
in Fig. 5.32. According to the effective detection area and detection efficiency of the
TSXS, the average X-ray photon flux of the Crab pulsar, statistically calculated by
using the first batch of observation data from the XPNAV-1, is 1.51 ph/cm
2 /s, while
the nominal value of X-ray photon flux of the Crab pulsar is 1.54 ph/cm
2 /s generally.
Apparently, both are almost same. Meanwhile, the energy-spectrum analysis results
of the Crab pulsar within the energy band of 0.5−10 keV are shown in Fig. 5.33,
where the horizontal axis is expressed with the common logarithm of energy. From
Fig. 5.33, it can be seen that the highest X-ray photon flux radiated by the Crab
pulsar occurs near the energy of 1 keV, and there is a peak value at energy of 10 keV,
resulting from cumulatively counting the high-energy particles with the energy of