54
2 Observations of Radio and X-ray Pulsars
antennas in Beijing Municipality, Delingha MM wave telescope with a diameter of
13.7 min Qinghai Province, Sheshan 25-m and 65-m radio telescopes in Shanghai
Municipality, Ulumuqi 25-m radio telescope in Xinjiang Uygur Autonomous Region
and Kunming 40-m radio telescope in Yunnan Province. Particularly, the world’s
largest fill-aperture radio telescope, FAST, located at the Dawodang depression in
Pingtang County, Guizhou Province, southwest China, was completed in September
2016. The FAST has a fixed primary reflector put in a natural sinkhole in the karst
topographical regions, focusing radio waves on a receiving antenna in a lightweight
feed cabin suspended 140-m above it. The reflector is composed of 4450 perforated
aluminum triangular panels, supported by a mesh of steel cables hanging from the
rims. 2225 winches make the reflector an active surface, pulling on joints between
the panels, deforming the flexible steel cable support into a parabolic antenna aligned
with the desired sky direction. The feed cabin can be moved by a cable robot using
winch servomechanism on six support towers. The receiving antennas are installed at
the Stewart platform below the feed cabin, which provides fine position control and
compensates for disturbances like wind. The working frequency range of the FAST
is 70 MHz−3 GHz and its observable sky area is a 40° cone at the local zenith. The
advantages of the FAST are large aperture, wide frequency band and high sensitivity.
The FAST is mainly applied to surveying the large-scale neutral hydrogen extending
to the edge of the universe, discovering the fainter radio pulsars, detecting the gravitational waves, searching the extra terrestrial intelligence and creating the pulsar
timing array. On the one hand, the characteristics of high sensitivity and large sky
coverage are very advantageous to the discovery of faint radio pulsars, millisecond
pulsars, binary systems, planetary systems with pulsars, extra-galactic strong pulsars
and non-globular cluster millisecond pulsars. On the other hand, the characteristics of
non-integral high sensitivity are specially applied to studying polarization and single
pulse of pulsars, accurately detecting interstellar medium and revealing radiation
mechanism and genesis of pulsars.
2.4 Investigations into Radio Pulsars
2.4.1 Discovery of the First Binary Pulsar System
During several years since discovering the first pulsar, there had been more than 100
pulsars found successively. In 1974, Russell Alan Hulse (1950−), a research student
from the University of Massachusetts Amherst, was working with his supervisor
Joseph Hooton Taylor (1941−) on a large-scale survey for pulsars using the Arecibo
305-m antenna. They found out 40 new pulsars in 140 square degrees sky area. These
pulsars had stable periodicity and their periodic change rates were mostly from 10
–12
to 10
–20 s/s. For the pulsars with so small periodic change rates, it is generally very
difficult to find out their periodic changes during several days.
2 Observations of Radio and X-ray Pulsars
antennas in Beijing Municipality, Delingha MM wave telescope with a diameter of
13.7 min Qinghai Province, Sheshan 25-m and 65-m radio telescopes in Shanghai
Municipality, Ulumuqi 25-m radio telescope in Xinjiang Uygur Autonomous Region
and Kunming 40-m radio telescope in Yunnan Province. Particularly, the world’s
largest fill-aperture radio telescope, FAST, located at the Dawodang depression in
Pingtang County, Guizhou Province, southwest China, was completed in September
2016. The FAST has a fixed primary reflector put in a natural sinkhole in the karst
topographical regions, focusing radio waves on a receiving antenna in a lightweight
feed cabin suspended 140-m above it. The reflector is composed of 4450 perforated
aluminum triangular panels, supported by a mesh of steel cables hanging from the
rims. 2225 winches make the reflector an active surface, pulling on joints between
the panels, deforming the flexible steel cable support into a parabolic antenna aligned
with the desired sky direction. The feed cabin can be moved by a cable robot using
winch servomechanism on six support towers. The receiving antennas are installed at
the Stewart platform below the feed cabin, which provides fine position control and
compensates for disturbances like wind. The working frequency range of the FAST
is 70 MHz−3 GHz and its observable sky area is a 40° cone at the local zenith. The
advantages of the FAST are large aperture, wide frequency band and high sensitivity.
The FAST is mainly applied to surveying the large-scale neutral hydrogen extending
to the edge of the universe, discovering the fainter radio pulsars, detecting the gravitational waves, searching the extra terrestrial intelligence and creating the pulsar
timing array. On the one hand, the characteristics of high sensitivity and large sky
coverage are very advantageous to the discovery of faint radio pulsars, millisecond
pulsars, binary systems, planetary systems with pulsars, extra-galactic strong pulsars
and non-globular cluster millisecond pulsars. On the other hand, the characteristics of
non-integral high sensitivity are specially applied to studying polarization and single
pulse of pulsars, accurately detecting interstellar medium and revealing radiation
mechanism and genesis of pulsars.
2.4 Investigations into Radio Pulsars
2.4.1 Discovery of the First Binary Pulsar System
During several years since discovering the first pulsar, there had been more than 100
pulsars found successively. In 1974, Russell Alan Hulse (1950−), a research student
from the University of Massachusetts Amherst, was working with his supervisor
Joseph Hooton Taylor (1941−) on a large-scale survey for pulsars using the Arecibo
305-m antenna. They found out 40 new pulsars in 140 square degrees sky area. These
pulsars had stable periodicity and their periodic change rates were mostly from 10
–12
to 10
–20 s/s. For the pulsars with so small periodic change rates, it is generally very
difficult to find out their periodic changes during several days.