Globular clusters are highly efficient radio pulsar factories. These pulsars can be used as precision probes of the clusters structure, gas content, magnetic field, and formation history; some of them are also highly interesting in their own right be
cause they probe exotic stellar evolution scenarios as well as the physics of dense matter, accretion, and gravity. Deep searches with SKA1-MID and SKA1-LOW will plausibly double to triple the known population. Such searches will only require one to a few tied-array beams, and can be done during early commissioning of the telescope - before an all-sky pulsar survey using hundreds to thousands of tied-array beams is feasible. With SKA2 it will be possible to observe most of the active radio pulsars within a large fraction of the Galactic globular clusters, an estimated population of 600 - 3700 observable pulsars (those beamed towards us). This rivals the total population of millisecond pulsars that can be found in the Galactic field; fully characterizing it will provide the best-possible physical laboratories as well as a rich dynamical history of the Galactic globular cluster system.
Pulsars emit low-frequency radio waves through to high-energy gamma-rays that are generated anywhere from the surface out to the edges of the magnetosphere. Detecting correlated mode changes in the multi-wavelength emission is therefore key to unders
tanding the physical relationship between these emission sites. Through simultaneous observations, we have detected synchronous switching in the radio and X-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio bright mode, the X-rays show only an un-pulsed, non-thermal component. Conversely, when the pulsar is in a radio quiet mode, the X-ray luminosity more than doubles and a 100%-pulsed thermal component is observed along with the non-thermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories.
The ROSAT X-ray source 1RXS J141256.0+792204 has recently been identified as a likely compact object whose properties suggest it could be a very nearby radio millisecond pulsar at d = 80 - 260pc. We investigated this hypothesis by searching for radio
pulsations using the Westerbork Synthesis Radio Telescope. We observed 1RXS J141256.0+792204 at 385 and 1380MHz, recording at high time and frequency resolution in order to maintain sensitivity to millisecond pulsations. These data were searched both for dispersed single pulses and using Fourier techniques sensitive to constant and orbitally modulated periodicities. No radio pulsations were detected in these observations, resulting in pulsed radio luminosity limits of L_400 ~ 0.3 (d/250pc)^2 mJy kpc^2 and L_1400 ~ 0.03 (d/250pc)^2 mJy kpc^2 at 400 and 1400MHz respectively. The lack of detectable radio pulsations from 1RXS J141256.0+792204 brings into question its identification as a nearby radio pulsar, though, because the pulsar could be beamed away from us, this hypothesis cannot be strictly ruled out.
We have surveyed all 22 known Galactic globular clusters observable with the Arecibo radio telescope and within 70kpc of the Sun for radio pulsations at ~1.4GHz. Data were taken with the Wideband Arecibo Pulsar Processor, which provided the large ban
dwidth and high time and frequency resolution needed to detect fast-spinning, faint pulsars. We have also employed advanced search techniques to maintain sensitivity to short orbital period binaries. These searches have discovered 11 new millisecond pulsars and 2 promising candidates in 5 clusters, almost doubling the population of pulsars in the Arecibo-visible globular clusters. Ten of these new pulsars are in binary systems, and 3 are eclipsing. This survey has discovered significantly more very fast-spinning pulsars (P_spin <~ 4ms) and short orbital period systems (P_orb <~ 6hr) than previous surveys of the same clusters. We discuss some properties of these systems, as well as some characteristics of the globular cluster pulsar population in general, particularly its luminosity distribution.
