Bibcode
Goicoechea, L. J.; Buitrago, J.; Oscoz, A.; Mediavilla, E.
Referencia bibliográfica
Astronomy and Astrophysics, v.303, p.502
Fecha de publicación:
11
1995
Revista
Número de citas
2
Número de citas referidas
2
Descripción
We study the delay induced by gravitational light bending in the arrival
times of signals emitted by an anisotropic source in rotation (pulsar).
The shift of the direction of the allowed pulsar beam (a vector defined
by the null geodesic connecting the pulsar to the observer) with orbital
phase induces a delay arising from the movement of the pulsar in its
orbit (orbital aberration) and another of gravitational origin
(gravitational shift delay). The delay due to the orbital aberration has
the same dependence on orbital phase as the purely geometric orbital
delay and is therefore unobservable. We derive a pulse-timing model for
pulsars in massive binaries with high inclination (i=π/2) and
negligible eccentricity, adding to the well-known contributions
(orbital, Shapiro and non-observable orbital aberration) an extra delay
produced by the gravitational shift of the allowed pulsar beam and by an
additional (and measurable) term of aberration which appears when the
number of pulses is used to define the coordinate time of emission in
the pulse-timing model. From the ratio of the pulsar period P to the
orbital length L (in c=1 units), the extra and the Shapiro delays are
compared. If P/L>=1, the extra delay is the dominant one. Some
high-mass X-ray binaries (e.g. Vela X-1) may be ideal scenarios for
measuring the extra delay and testing whether pulsars are indeed
rotating beacons. However, for X-ray binaries with long pulsar periods,
the arrival times are poorly determined and this effect cannot be
observed. For high-mass radio binaries, the uncertainties in the
determination of the pulse arrival time are small, but the amplitude of
the extra delay is also small. The possible discovery of binary pulsars
with short periods and significant values of P/L (or the improvement in
the measure of arrival times) should allow the observation of this
interesting effect involving gravitation and aberration.