4.5 Going further 

For further details on the technical details and prospects of pulsar timing, the interested reader is referred to a number of excellent review articles [19, 148, 103, 25, 26]. An up-to-date list summarising the various timing programmes is kept by Don Backer [11]. Two freely available software packages which are routinely used for such analyses amongst the pulsar community are also available viz:  TEMPO [152, 4] and TIMAPR [57, 12]. These packages are based on more detailed versions of the timing model outlined in § 4.2 .

The remarkable precision of these measurements, particularly for millisecond pulsars, allows the detection of radial accelerations on the pulsar induced by orbiting bodies smaller than the Earth. Alex Wolszczan detected one such ``pulsar planetary system'' in 1990 following the discovery of a 6.2 ms pulsar B1257+12. In this case, the pulsar is orbited by at least two Earth-mass bodies [168, 2]. Subsequent measurements of B1257+12 were even able to measure resonance interactions between two of the planets [167], confirming the nature of the system beyond all doubt. Long-term timing measurements of the 11 ms pulsar B1620-26 in the globular cluster M4 indicate that it may also have a planetary companion [155, 18]. For detailed reviews of these systems, and their implications for planetary formation scenarios, the interested reader is referred to [124].

Binary and Millisecond Pulsars D. R. Lorimer (dunc@mpifr-bonn.mpg.de) http://www.livingreviews.org/lrr-1998-10 © Max-Planck-Gesellschaft. ISSN 1433-8351 Problems/Comments to livrev@aei-potsdam.mpg.de