Millisecond pulsars

3.3 Millisecond pulsars

The population of known millisecond pulsars (MSPs) is one of the fastest growing populations of relativistic binaries in globular clusters. Several ongoing searches are continuing to reveal millisecond pulsars in a number of globular clusters. Previous searches have used deep multifrequency imaging to estimate the population of pulsars in globular clusters [71

]. In this approach, the expected number of pulsars beaming toward the earth, $Npuls$ , 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 $Lmin$ and the total luminosity observed is $L tot$ , then, with simple assumptions on the neutron star luminosity function,

In their observations of 7 globular clusters, Fruchter and Goss have recovered previously known pulsars in NGC 6440, NGC 6539, NGC 6624, and 47 Tuc [71

]. Their estimates based on Equation (12

) give evidence of a population of between 60 and 200 previously unknown pulsars in Terzan 5, and about 15 each in Liller 1 and NGC 6544 [71 ].

Current searches include the following: Arecibo, which is searching over 22 globular clusters [104 ]; Green Bank Telescope (GBT), which is working alone and in conjunction with Arecibo [123 , 104 ]; the Giant Metrewave Radio Telescope (GMRT), which is searching over about 10 globular clusters [66 ]; and Parkes, which is searching over 60 globular clusters [40 ]. Although these searches have been quite successful, they are still subject to certain selection effects such as distance, dispersion measure, and acceleration in compact binaries [28 ]. For an excellent review of the properties of all pulsars in globular clusters, see the review by Camilo and Rasio [28 ] and references therein. The properties of known pulsars in binary systems with orbital period less than one day are listed in Table 2, which has been extracted from the online catalog maintained by Freire [64 ].Update

With the ongoing searches, it can be reasonably expected that the number of millisecond pulsars in binary systems in globular clusters will continue to grow in the coming years.

Table 2:

Short orbital period binary millisecond pulsars in globular clusters. Host clusters and orbital properties. See

http://www.naic.edu/~pfreire/GCpsr.html for references to each pulsar.Update



Pulsar	$Pspin$	Cluster	$Porb$	$e$	$M2$
	(ms)		(days)		( $M ⊙$ )

J0024–7204I	3.485	47 Tuc	0.229	$<$ 0.0004	0.015
J0023–7203J	2.101	47 Tuc	0.121	$<$ 0.00004	0.024
J0024–7204O	2.643	47 Tuc	0.136	$<$ 0.00016	0.025
J0024–7204P	3.643	47 Tuc	0.147	—	0.02
J0024–7204R	3.480	47 Tuc	0.066	—	0.030
J0024–7203U	4.343	47 Tuc	0.429	0.000015	0.14
J0024–7204V	4.810	47 Tuc	0.227	—	0.34(?)
J0024–7204W	2.352	47 Tuc	0.133	—	0.14
J0024–7204Y	2.196	47 Tuc	0.522	—	0.16
J1518+0204C	2.484	M5	0.087	—	0.038
J1641+3627D	3.118	M13	0.591	—	0.18
J1641+3627E	2.487	M13	0.118	—	0.02
J1701–3006B	3.594	M62	0.145	$<$ 0.00007	0.14
J1701–3006C	3.806	M62	0.215	$<$ 0.00006	0.08
J1701–3006E	3.234	M62	0.16	—	0.035
J1701–3006F	2.295	M62	0.20	—	0.02
B1718–19	1004.03	NGC 6342	0.258	$<$ 0.005	0.13
J1748–2446A	11.563	Terzan 5	0.076	—	0.10
J1748–2446M	3.569	Terzan 5	0.443	—	0.16
J1748–2446N	8.667	Terzan 5	0.386	0.000045	0.56
J1748–2446O	1.677	Terzan 5	0.259	—	0.04
J1748–2446P	1.729	Terzan 5	0.363	—	0.44
J1748–2446V	2.073	Terzan 5	0.504	—	0.14
J1748–2446ae	3.659	Terzan 5	0.171	—	0.019
J1748–2021D	13.496	NGC6440	0.286	—	0.14
J1807–2459A	3.059	NGC 6544	0.071	—	0.010
J1824–2452G	5.909	M28	0.105	—	0.011
J1824–2452H	4.629	M28	0.435	—	0.2
J1824–2452J	4.039	M28	0.097	—	0.015
J1905+0154A	3.193	NGC6749	0.813	—	0.09
J1911–5958A	3.266	NGC 6752	0.837	$<$ 0.00001	0.22
J1911+0102A	3.619	NGC 6760	0.141	$<$ 0.00013	0.02
J1953+1846A	4.888	M71	0.177	—	0.032
B2127+11C	30.529	M 15	0.335	0.681	1.13
J2140–2310A	11.019	M30	0.174	$<$ 0.00012	0.11