Chapter 2
General Relativity Measurements
from Pulsars
Marta Burgay, Delphine Perrodin, and Andrea Possenti
Contents
2.1 Why Radio Pulsars . .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 54
2.2 The Many Faces of the Radio Pulsar Zoo .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 55
2.2.1 Radio Pulsars. . .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 55
2.2.2 Intermittent Pulsars . .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 59
2.2.3 Rotating RAdio Transients . .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 61
2.3 Relativistic Binary Pulsars . .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 62
2.3.1 Basic Evolution . .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 62
2.3.2 The Current Sample .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 66
2.4 Pulsar Timing Basics . .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 72
2.4.1 Timing Procedure: Measurement of the ToAs. . .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 72
2.4.2 Timing Procedure: Modelling the ToAs .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 74
2.5 Probing Relativistic Gravity with Pulsars .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 78
2.5.1 Tests Using PPN Parameters . ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 80
2.5.2 Tests Using PK Parameters . .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 82
2.5.3 Future Prospects .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 88
References . .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 90
Abstract In this chapter, after a brief description of radio pulsars and their different
manifestations, we illustrate the case of the so-called relativistic binary pulsars,
which are fast-spinning neutron stars in orbit with a compact companion star, either
a white dwarf or a second neutron star. Thanks to the clock-like nature of their radio
signals, some of these binary pulsars can be used as test beds for General Relativity
and other theories of gravity. We describe the methodology used to exploit these
sources as laboratories for relativistic gravity and review some of the most important
recent results in this field of research.
M. Burgay () · D. Perrodin · A. Possenti
INAF-Osservatorio Astronomico di Cagliari, Selargius, CA, Italy
e-mail: burgay@oa-cagliari.inaf.it; delphine@oa-cagliari.inaf.it; possenti@oa-cagliari.inaf.it
© Springer-Verlag GmbH Germany, part of Springer Nature 2021
T. M. Belloni et al. (eds.), Timing Neutron Stars: Pulsations, Oscillations
and Explosions, Astrophysics and Space Science Library 461,
https://doi.org/10.1007/978-3-662-62110-3_2
53
General Relativity Measurements
from Pulsars
Marta Burgay, Delphine Perrodin, and Andrea Possenti
Contents
2.1 Why Radio Pulsars . .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 54
2.2 The Many Faces of the Radio Pulsar Zoo .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 55
2.2.1 Radio Pulsars. . .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 55
2.2.2 Intermittent Pulsars . .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 59
2.2.3 Rotating RAdio Transients . .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 61
2.3 Relativistic Binary Pulsars . .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 62
2.3.1 Basic Evolution . .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 62
2.3.2 The Current Sample .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 66
2.4 Pulsar Timing Basics . .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 72
2.4.1 Timing Procedure: Measurement of the ToAs. . .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 72
2.4.2 Timing Procedure: Modelling the ToAs .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 74
2.5 Probing Relativistic Gravity with Pulsars .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 78
2.5.1 Tests Using PPN Parameters . ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 80
2.5.2 Tests Using PK Parameters . .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 82
2.5.3 Future Prospects .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 88
References . .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 90
Abstract In this chapter, after a brief description of radio pulsars and their different
manifestations, we illustrate the case of the so-called relativistic binary pulsars,
which are fast-spinning neutron stars in orbit with a compact companion star, either
a white dwarf or a second neutron star. Thanks to the clock-like nature of their radio
signals, some of these binary pulsars can be used as test beds for General Relativity
and other theories of gravity. We describe the methodology used to exploit these
sources as laboratories for relativistic gravity and review some of the most important
recent results in this field of research.
M. Burgay () · D. Perrodin · A. Possenti
INAF-Osservatorio Astronomico di Cagliari, Selargius, CA, Italy
e-mail: burgay@oa-cagliari.inaf.it; delphine@oa-cagliari.inaf.it; possenti@oa-cagliari.inaf.it
© Springer-Verlag GmbH Germany, part of Springer Nature 2021
T. M. Belloni et al. (eds.), Timing Neutron Stars: Pulsations, Oscillations
and Explosions, Astrophysics and Space Science Library 461,
https://doi.org/10.1007/978-3-662-62110-3_2
53