72
M. Burgay et al.
exclusively) related to relativistic gravity, hence, strictly speaking, they are not
relativistic binaries: the measured ˙
ω of J1740−3052, for instance, is likely due to a
mixture of relativistic orbital precession and precession due to spin quadrupole of
the massive companion [64], while the orbital decay measured in J0045−7319 is
likely caused by tidal effects of a retrograde rotation of the companion [65].
For the pulsars for which the measured ˙
P b is positive, marked with b in Table 2.1,
the variation of the orbital period is certainly not relativistic (loss of energy in
the form of gravitational waves would lead to a shrinkage of the orbit). For PSR
J1023+0038, for instance, [30], the positive value is due to mass loss in the system,
while in other cases it is given by kinematic effects (acceleration in the Galactic
potential and/or proper motion of the pulsar; e.g. [66]).
2.4 Pulsar Timing Basics
At the time of the discovery of a new pulsar, only the spin period P , dispersion
measure DM and position are approximately measured. The latter, for instance, is
initially determined with an uncertainty of the order of the size of the beam of the
radio telescope used for the discovery. Combining the approximate value of DM
and celestial position with a model for the electron distribution in the Galaxy (e.g.
[4, 5, 67]), one can also get a rough estimate of the pulsar’s distance.
To get a precise measurement of all the rotational, astrometric and, in case of
a binary system, orbital parameters of any newly-discovered pulsar, it is necessary
to start a follow-up procedure called timing, which will be briefly described in this
section. The best results of pulsar timing are obtained for the most stable rotators, in
general the fastest spinning pulsars. A high flux density, allowing a more precise
determination of the “Times of Arrival” (ToAs) of the radio pulses, is also an
advantage for accurate timing. As we will see, long-term timing studies of rapidlyrotating recycled pulsars are hence a powerful observational tool for performing a
variety of experiments in fundamental physics, in particular for the investigation of
relativistic gravity and for gravitational wave detection.
Chapters 7 and 8 of [68], and Chapters 4 and 5 of [69] can be used as references
for a full description of pulsar timing procedures. In this chapter, we focus on the
basic concepts and main operational steps.
2.4.1 Timing Procedure: Measurement of the ToAs
Experimentally, timing a pulsar means observing it semi-regularly to measure,
for each observing epoch, one or more Times of Arrival (ToAs) of a specific
recognisable feature—usually the peak—in the pulse phase-averaged radio light
curve (the pulse profile). For different pulsars, depending on the specific aim of
the experiment, a timing campaign can last from a year—the minimum time-
M. Burgay et al.
exclusively) related to relativistic gravity, hence, strictly speaking, they are not
relativistic binaries: the measured ˙
ω of J1740−3052, for instance, is likely due to a
mixture of relativistic orbital precession and precession due to spin quadrupole of
the massive companion [64], while the orbital decay measured in J0045−7319 is
likely caused by tidal effects of a retrograde rotation of the companion [65].
For the pulsars for which the measured ˙
P b is positive, marked with b in Table 2.1,
the variation of the orbital period is certainly not relativistic (loss of energy in
the form of gravitational waves would lead to a shrinkage of the orbit). For PSR
J1023+0038, for instance, [30], the positive value is due to mass loss in the system,
while in other cases it is given by kinematic effects (acceleration in the Galactic
potential and/or proper motion of the pulsar; e.g. [66]).
2.4 Pulsar Timing Basics
At the time of the discovery of a new pulsar, only the spin period P , dispersion
measure DM and position are approximately measured. The latter, for instance, is
initially determined with an uncertainty of the order of the size of the beam of the
radio telescope used for the discovery. Combining the approximate value of DM
and celestial position with a model for the electron distribution in the Galaxy (e.g.
[4, 5, 67]), one can also get a rough estimate of the pulsar’s distance.
To get a precise measurement of all the rotational, astrometric and, in case of
a binary system, orbital parameters of any newly-discovered pulsar, it is necessary
to start a follow-up procedure called timing, which will be briefly described in this
section. The best results of pulsar timing are obtained for the most stable rotators, in
general the fastest spinning pulsars. A high flux density, allowing a more precise
determination of the “Times of Arrival” (ToAs) of the radio pulses, is also an
advantage for accurate timing. As we will see, long-term timing studies of rapidlyrotating recycled pulsars are hence a powerful observational tool for performing a
variety of experiments in fundamental physics, in particular for the investigation of
relativistic gravity and for gravitational wave detection.
Chapters 7 and 8 of [68], and Chapters 4 and 5 of [69] can be used as references
for a full description of pulsar timing procedures. In this chapter, we focus on the
basic concepts and main operational steps.
2.4.1 Timing Procedure: Measurement of the ToAs
Experimentally, timing a pulsar means observing it semi-regularly to measure,
for each observing epoch, one or more Times of Arrival (ToAs) of a specific
recognisable feature—usually the peak—in the pulse phase-averaged radio light
curve (the pulse profile). For different pulsars, depending on the specific aim of
the experiment, a timing campaign can last from a year—the minimum time-