Preface
The study of neutron stars is important in several aspects. On the astrophysical
side, from their birth from supernova events to their evolution when isolated or
in binary systems, they constitute an important end point of stellar evolution. In
accreting binaries, they provide an important class of objects for our understanding
of accretion onto compact objects, together with black-hole binaries. We now know
transitional objects between accreting neutron stars and radio pulsars that can help
us understand better both classes of sources. On the physical side, they constitute
formidable and unique laboratories to study fundamental processes. First, they are
the only objects in the Universe where matter is at extremely high density and
we still do not know the associated equation of state. Second, they offer us the
possibility to study their internal structure, affected by high angular momentum
and large magnetic field. Third, but not least, they are being used as test objects
for experimental measurements of the effects of general relativity (GR). Binary
pulsars provide very precise clocks to monitor the orbit of the object and detect
modifications due to GR, while in accreting neutron stars the strength of the
gravitational field close to the compact object modifies the properties of accretion
giving us the possibility to study GR in the strong-field regime.
All these studies are based on the time variability of the flux, from the radio band
to X-rays. This book is focused on timing aspects. As the title says, this variability
is in three forms. Pulsations, observed historically from radio pulsars, but now
detected also in accreting low-mass X-ray binaries, the progenitors of millisecond
pulsars. Oscillations, from the noisy variability of accreting systems, where strong
quasi-periodicities are observed at a period of a few milliseconds, comparable to
the dynamical time close to the surface of the neutron star. Explosions, powerful
nuclear-powered X-ray bursts that take place on the surface of accreting neutron
stars when the accretion level is in the favorable range.
Merate, Italy
Tomaso M. Belloni
Groningen, The Netherlands
Mariano Méndez
Beijing, China
Chengmin Zhang
June 2020
v
The study of neutron stars is important in several aspects. On the astrophysical
side, from their birth from supernova events to their evolution when isolated or
in binary systems, they constitute an important end point of stellar evolution. In
accreting binaries, they provide an important class of objects for our understanding
of accretion onto compact objects, together with black-hole binaries. We now know
transitional objects between accreting neutron stars and radio pulsars that can help
us understand better both classes of sources. On the physical side, they constitute
formidable and unique laboratories to study fundamental processes. First, they are
the only objects in the Universe where matter is at extremely high density and
we still do not know the associated equation of state. Second, they offer us the
possibility to study their internal structure, affected by high angular momentum
and large magnetic field. Third, but not least, they are being used as test objects
for experimental measurements of the effects of general relativity (GR). Binary
pulsars provide very precise clocks to monitor the orbit of the object and detect
modifications due to GR, while in accreting neutron stars the strength of the
gravitational field close to the compact object modifies the properties of accretion
giving us the possibility to study GR in the strong-field regime.
All these studies are based on the time variability of the flux, from the radio band
to X-rays. This book is focused on timing aspects. As the title says, this variability
is in three forms. Pulsations, observed historically from radio pulsars, but now
detected also in accreting low-mass X-ray binaries, the progenitors of millisecond
pulsars. Oscillations, from the noisy variability of accreting systems, where strong
quasi-periodicities are observed at a period of a few milliseconds, comparable to
the dynamical time close to the surface of the neutron star. Explosions, powerful
nuclear-powered X-ray bursts that take place on the surface of accreting neutron
stars when the accretion level is in the favorable range.
Merate, Italy
Tomaso M. Belloni
Groningen, The Netherlands
Mariano Méndez
Beijing, China
Chengmin Zhang
June 2020
v