An approach by Fruchter and Goss [51] uses deep
multifrequency imaging to estimate the population of pulsars in
globular clusters. In this approach, the expected number of pulsars
beaming toward the earth,
, is determined by the total
radio luminosity observed when the radio beam width is comparable
in diameter to the core of the cluster. If the minimum pulsar
luminosity is
and the total luminosity observed is
, then, with simple assumptions on the neutron star
luminosity function,
Chandra imaging of 47 Tuc has also recovered
those 15 MSPs with precise radio positions [64]. One of these has
now been identified with an optical counterpart that is almost
certainly a He white dwarf [40]. The X-ray
spectral and temporal characteristics of these suggest that over 50
of the 108 X-ray sources identified in 47 Tuc are millisecond
pulsars [64].
To obtain a full understanding of the nature of
millisecond pulsars, it is necessary to develop full timing
solutions so that the orbits can be determined. Work has begun on
the MSPs in 47 Tuc, and Freire et
al. [48] have obtained
timing solutions for 15 of the known pulsars, including 8 binary
systems. The properties of all the globular cluster MSPs with
orbital periods less than 1 day are given in Table 2, which is a subset of
Table 5 in Lorimer [98
].
Table 2: | Short orbital period binary millisecond pulsars in globular clusters. Host clusters and orbital properties. |
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Pulsar
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Cluster |
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Ref. | |||||
(ms)
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(days)
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J0024 | -7204I | 3. | 485 | 47 Tuc | 0. | 23 | ![]() |
001 | 0. | 01 | [20![]() ![]() |
J0023 | -7203J | 2. | 101 | 47 Tuc | 0. | 12 | ![]() |
0002 | 0. | 02 | [20![]() ![]() |
J0024 | -7204O | 2. | 643 | 47 Tuc | 0. | 14 | ![]() |
004 | 0. | 02 | [20![]() ![]() |
J0024 | -72R | 3. | 480 | 47 Tuc | 0. | 066 | ![]() |
0 | 0. | 03 | [20![]() |
J0024 | -7203U | 4. | 343 | 47 Tuc | 0. | 43 | 0. | 0002 | .. | . | [20![]() |
J0024 | -72W | 2. | 352 | 47 Tuc | 0. | 11 | ![]() |
0 | 0. | 15 | [20] |
B1718 | -19 | 1004. | 037 | NGC 6342 | 0. | 26 | ![]() |
0 | 0. | 1 | [100] |
B1744 | -24A | 11. | 563 | Terzan 5 | 0. | 08 | ![]() |
0 | 0. | 1 | [101, 114] |
J1807 | -24 | 3. | 059 | NGC 6544 | 0. | 071 | ![]() |
0 | 0. | 009 | [29![]() |
J1910 | -59 | 3. | 266 | NGC 6752 | 0. | 865 | ![]() |
0 | 0. | 19 | [29] |
J1910 | +0004 | 3. | 619 | NGC 6760 | 0. | 14 | ![]() |
0 | 0. | 02 | [35] |
B2127 | +11C | 30. | 529 | M 15 | 0. | 34 | 0. | 68 | 0. | 9 | [6] |
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With the ongoing Parkes multi-beam surveys of
globular clusters and the use of the acceleration
technique [98, 108], the
population of known MSPs will be expected to grow dramatically in
the next few years. This will help improve the understanding of
these objects and their progenitors as well as the dynamics of
globular clusters.