68
M. Burgay et al.
itself. Following this simple definition, the total number of published binaries with
measured PK parameters to date is 72 (see Table 2.1).
Among these, 12 have a neutron star companion: J0453+1559 [40], a DNS
system with a large mass asymmetry, J0737−3039A [41] and J0737−3039B [42],
composing the first (and so far the only) double pulsar system (see Sect. 2.5.2.2);
J1518+4904 [43]; B1534+12 [44, 45] and J1756−2251 [46], the only other DNSs
besides the double pulsar for which all 5 post-Keplerian parameters have been
measured; J1811−1736 [47, 48]; J1829+2456 [49]; J1906+0746 [50], whose
undetected companion is likely the recycled pulsar in the system; B1913+16, the
first known binary pulsar, whose discoverers were awarded the Nobel prize for
physics in 1993 [51, 52]; J1930−1852 [53], belonging to the widest DNS system
known, and J2129+1210C in the globular cluster M15 [54, 55].
The rest of the sample is mostly composed of NS–WD systems, with the
remarkable case of J0348−0432 [56], for which timing measurements, coupled
with time-resolved optical spectroscopy, allowed astronomers to derive that the
neutron star has a mass very close to 2 solar masses (2.01 ± 0.04 M ) [57],
which is the highest neutron star mass yet measured with such accuracy. This
constrains the equation of state for nuclear matter, effectively ruling out the softest
equations of state. As for the masses of the companion star in NS–WD systems, they
range from ∼1 M (typically Carbon-Oxygen WDs) to 0.02 M (typically Helium
WDs). Among the pulsars with a heavy WD companion, two, J1141−6545 [58]
and J2305+4707 [59] (believed for a long time to be part of a DNS system) have
relatively long spin periods, suggestive of the fact that they have not been recycled
by accretion from the companion star. The NS–WD binary J1738+0333 is so far
the best pulsar for constraining tensor-scalar theories because of a very precise
determination of its orbital decay PK parameter, as will be seen in Sect. 2.5.2.3
[60, 61]. The evolutionary path for these peculiar systems starts from two almost
equal mass stars, the more massive of which evolves first and transfers matter onto
the companion. The mass of the latter becomes higher than that of the primary, and
the subsequent evolution leads to a supernova explosion and to the formation of a
NS, which will emit as an ordinary pulsar. The initially more massive star, on the
other hand, after losing mass to the companion, has not enough mass anymore to
become a second NS and evolves into a heavy WD.
In the sample of Table 2.1, there are also a few binary systems with massive
main sequence companions, (e.g. J0045−7319 [62] and J1740−3052 [63]). The
post-Keplerian parameters measured for these pulsars, however, are not (or not
Fig. 2.10 (continued) bottom: main sequence—main sequence; first Roche lobe overflow (followed by a supernova explosion that leads to the formation of a NS, possibly shining as an ordinary
pulsar); second Roche lobe overflow (the NS shines as an X-ray pulsar and is spun up by the
accreted mass and angular momentum); end of the mass transfer: the NS shines as a fully recycled
millisecond pulsar and the secondary star is a white dwarf
M. Burgay et al.
itself. Following this simple definition, the total number of published binaries with
measured PK parameters to date is 72 (see Table 2.1).
Among these, 12 have a neutron star companion: J0453+1559 [40], a DNS
system with a large mass asymmetry, J0737−3039A [41] and J0737−3039B [42],
composing the first (and so far the only) double pulsar system (see Sect. 2.5.2.2);
J1518+4904 [43]; B1534+12 [44, 45] and J1756−2251 [46], the only other DNSs
besides the double pulsar for which all 5 post-Keplerian parameters have been
measured; J1811−1736 [47, 48]; J1829+2456 [49]; J1906+0746 [50], whose
undetected companion is likely the recycled pulsar in the system; B1913+16, the
first known binary pulsar, whose discoverers were awarded the Nobel prize for
physics in 1993 [51, 52]; J1930−1852 [53], belonging to the widest DNS system
known, and J2129+1210C in the globular cluster M15 [54, 55].
The rest of the sample is mostly composed of NS–WD systems, with the
remarkable case of J0348−0432 [56], for which timing measurements, coupled
with time-resolved optical spectroscopy, allowed astronomers to derive that the
neutron star has a mass very close to 2 solar masses (2.01 ± 0.04 M ) [57],
which is the highest neutron star mass yet measured with such accuracy. This
constrains the equation of state for nuclear matter, effectively ruling out the softest
equations of state. As for the masses of the companion star in NS–WD systems, they
range from ∼1 M (typically Carbon-Oxygen WDs) to 0.02 M (typically Helium
WDs). Among the pulsars with a heavy WD companion, two, J1141−6545 [58]
and J2305+4707 [59] (believed for a long time to be part of a DNS system) have
relatively long spin periods, suggestive of the fact that they have not been recycled
by accretion from the companion star. The NS–WD binary J1738+0333 is so far
the best pulsar for constraining tensor-scalar theories because of a very precise
determination of its orbital decay PK parameter, as will be seen in Sect. 2.5.2.3
[60, 61]. The evolutionary path for these peculiar systems starts from two almost
equal mass stars, the more massive of which evolves first and transfers matter onto
the companion. The mass of the latter becomes higher than that of the primary, and
the subsequent evolution leads to a supernova explosion and to the formation of a
NS, which will emit as an ordinary pulsar. The initially more massive star, on the
other hand, after losing mass to the companion, has not enough mass anymore to
become a second NS and evolves into a heavy WD.
In the sample of Table 2.1, there are also a few binary systems with massive
main sequence companions, (e.g. J0045−7319 [62] and J1740−3052 [63]). The
post-Keplerian parameters measured for these pulsars, however, are not (or not
Fig. 2.10 (continued) bottom: main sequence—main sequence; first Roche lobe overflow (followed by a supernova explosion that leads to the formation of a NS, possibly shining as an ordinary
pulsar); second Roche lobe overflow (the NS shines as an X-ray pulsar and is spun up by the
accreted mass and angular momentum); end of the mass transfer: the NS shines as a fully recycled
millisecond pulsar and the secondary star is a white dwarf