Discovery and study of exotic radio pulsars
Abstract
We have conducted both targeted and wide-field surveys for exotic radio pulsars using the Arecibo, Green Bank, and Parkes telescopes. A survey of 22 globular clusters with Arecibo has discovered 11 millisecond pulsars, almost doubling the number known in these clusters. Ten of the new pulsars are in binaries,
and 3 show eclipses. This survey has discovered significantly more very fast-spinning pulsars ( P spin [Special characters omitted.] 4 ms) and short orbital period systems ( P orb [Special characters omitted.] 6 hr) than previous surveys of the same clusters. We discuss some characteristics of the globular cluster pulsar population in general, particularly the luminosity function. In observations of the rich, massive cluster Terzan 5 with the Green Bank Telescope we have discovered the 1.396-ms pulsar J1748-2446ad, which is now the fastest-spinning neutron star known. The difficulty in detecting this pulsar, due to its very low flux density and high eclipse fraction (~40% of the orbit), suggests that even faster-spinning neutron stars exist. If the pulsar has a mass less than 2 M[Special characters omitted.] , then its non-rotating radius is constrained by the spin period to be < 16 km. The short period of this pulsar also constrains models that suggest gravitational radiation, through an r-mode instability, limits the maximum spin frequency of neutron stars. Arecibo and Parkes searches of 5 potential ASCA X-ray counterparts to unidentified EGRET g-ray sources have revealed the young, energetic pulsar J2021+3651. PSR J2021+3651 is associated with the X-ray source AX J2021.1+3651, which in turn is likely associated with the COS B g-ray source 2CG 075+00, also known as GeV J2020+3658 and 3EG J2021+3716. This solves the long-standing mystery of this source's nature. Subsequent X-ray imaging and timing of PSR J2021+3651 with the Chandra observatory revealed a pulsar wind nebula whose morphology is reminiscent of the equatorial tori seen around some young pulsars, along with thermal emission from an embedded point source ( kT oo = 0.15±0.02keV). An observation in continuousclocking mode reveals a possible pulse detection from the point source. Finally, we discuss two on-going, untargeted surveys of the Galactic Plane. These surveys hope to find exotic pulsars whose properties will elucidate the physics of pulsars, or which can potentially be used to study ultra-dense matter and strong gravity. The PALFA survey at Arecibo is using a 7-beam receiver at 1.4 GHz to cover the Arecibo-visible Galactic Plane. 28 pulsars have been discovered so far, including a few young, energetic pulsars and the youngest pulsar binary system known, PSR J1906+0746. The GBT350 survey at Green Bank is covering the Galactic Plane north of d ∼ 40°. Despite the 350-MHz observing frequency, the high resolution of these data allows us to maintain sensitivity to fast pulsars. Thus far, 14 pulsars have been discovered, 3 of which were found in time-domain searches for bright, dispersed bursts.- Publication:
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Ph.D. Thesis
- Pub Date:
- 2007
- Bibcode:
- 2007PhDT........28H
- Keywords:
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- Exotic radio pulsars;
- Pulsar discovery;
- Globular clusters;
- Pulsar physics;
- Ultradense matter;
- Strong gravity