56
2 Observations of Radio and X-ray Pulsars
2.4.2 Discovery of the First Millisecond Pulsar
In 1970s, there was radio source 4C21.53 in the Cambridge catalogue of radio
sources, and it has basic properties of pulsars, such as strong polarization, reducing
power spectrum and high compact, but its periodic pulse signals had never been
detected. Since at that time it was not considered that the rotating periods of pulsars
might get to millisecond order, most of radio telescopes were not sensitive to pulse
signals with periods of less than 10 ms. In 1982, an American astrophysicist, Donald
C. Backer (1943−2010), initiated a search in the region of 4C21.53, which would be
sensitive to a wide range of pulse periods and dispersion measures, including very
short periods. The initial search plan was to sample at a rate of 500 Hz, which would
have been insufficiently fast to detect a pulsar spinning at 642 Hz. To simplify the
search apparatus, Backer’s research team sampled as quickly as possible, and time
averaged the signal over a period of 0.4 ms, thus effectively sampling at 2500 Hz. As a
result, they eventually determined that the radio source was a pulsar, PSR B1937+21,
rotating every 1.558 milliseconds [1], a rate far beyond anything that astronomers
studying pulsars had expected. The PSR B1937+21 is the first discovered millisecond
pulsar, and its rotation along with other millisecond pulsars discovered later is very
stable in their rotations. These millisecond pulsars are capable of keeping time as
well as atomic clocks. In 1994, a Polish astronomer Aleksander Wolszczan (1946−)
pointed out that the PSR B1937+21 has a dwarf planetary companion within a range
of 2 AU, whose mass is about one-thousandth of the mass of Earth. Moreover, Xray signals emitted from PSR B1937+21 were also detected by the BeppoSAX [2],
an Italian–Dutch satellite for X-ray astronomy, successfully launched by an AtlasCentaur rocket into a 4-degree inclination low Earth orbit on April 30, 1996 and
ended its life falling into the Pacific Ocean on April 29, 2003. And thus, the PSR
B1937+21 is also a X-ray binary system.
2.4.3 Acceleration Mechanism and Application
of Millisecond Pulsars
Generally, it is shown from studies that all short periodic pulsars are young neutron
stars with strong magnetic fields, and their periodic change rates are also larger. There
is no longer thermonuclear reaction for an ordinary pulsar, and its radiations can be
kept only by consuming the rotating energy. As a result, the pulsar’s rotation speed
will be slower and slower, and its pulse period gradually increases. In other words,
with the pulsar’s age increasing, its period will be longer and longer. However, the
periods of millisecond pulsars are very short and stable, their characteristic ages
even get to 1000 million years, higher 5 orders than other pulsars with short periodic
periods. In the X-ray binary systems, the radiant energy of pulsars does not come
from consuming the rotating energy, but from accreting matter from the companions.
The accreted matter falls highly rapidly into neutron stars, and not only provides the
2 Observations of Radio and X-ray Pulsars
2.4.2 Discovery of the First Millisecond Pulsar
In 1970s, there was radio source 4C21.53 in the Cambridge catalogue of radio
sources, and it has basic properties of pulsars, such as strong polarization, reducing
power spectrum and high compact, but its periodic pulse signals had never been
detected. Since at that time it was not considered that the rotating periods of pulsars
might get to millisecond order, most of radio telescopes were not sensitive to pulse
signals with periods of less than 10 ms. In 1982, an American astrophysicist, Donald
C. Backer (1943−2010), initiated a search in the region of 4C21.53, which would be
sensitive to a wide range of pulse periods and dispersion measures, including very
short periods. The initial search plan was to sample at a rate of 500 Hz, which would
have been insufficiently fast to detect a pulsar spinning at 642 Hz. To simplify the
search apparatus, Backer’s research team sampled as quickly as possible, and time
averaged the signal over a period of 0.4 ms, thus effectively sampling at 2500 Hz. As a
result, they eventually determined that the radio source was a pulsar, PSR B1937+21,
rotating every 1.558 milliseconds [1], a rate far beyond anything that astronomers
studying pulsars had expected. The PSR B1937+21 is the first discovered millisecond
pulsar, and its rotation along with other millisecond pulsars discovered later is very
stable in their rotations. These millisecond pulsars are capable of keeping time as
well as atomic clocks. In 1994, a Polish astronomer Aleksander Wolszczan (1946−)
pointed out that the PSR B1937+21 has a dwarf planetary companion within a range
of 2 AU, whose mass is about one-thousandth of the mass of Earth. Moreover, Xray signals emitted from PSR B1937+21 were also detected by the BeppoSAX [2],
an Italian–Dutch satellite for X-ray astronomy, successfully launched by an AtlasCentaur rocket into a 4-degree inclination low Earth orbit on April 30, 1996 and
ended its life falling into the Pacific Ocean on April 29, 2003. And thus, the PSR
B1937+21 is also a X-ray binary system.
2.4.3 Acceleration Mechanism and Application
of Millisecond Pulsars
Generally, it is shown from studies that all short periodic pulsars are young neutron
stars with strong magnetic fields, and their periodic change rates are also larger. There
is no longer thermonuclear reaction for an ordinary pulsar, and its radiations can be
kept only by consuming the rotating energy. As a result, the pulsar’s rotation speed
will be slower and slower, and its pulse period gradually increases. In other words,
with the pulsar’s age increasing, its period will be longer and longer. However, the
periods of millisecond pulsars are very short and stable, their characteristic ages
even get to 1000 million years, higher 5 orders than other pulsars with short periodic
periods. In the X-ray binary systems, the radiant energy of pulsars does not come
from consuming the rotating energy, but from accreting matter from the companions.
The accreted matter falls highly rapidly into neutron stars, and not only provides the