Variability of 19 Millisecond Pulsars in 47 Tucanae withChandraHRC‐S

We present results from our 830 ksec observation of the globular cluster 47Tucanae with the Chandra X-ray Observatory's High Resolution Camera-S. We limitour analysis here to the 19 previously known, localized millisecond pulsars(MSPs) in the cluster. This work more than doubles the sample of X-ray-detectedMSPs observed with sensitivity to rotational variability; it is also the firstsurvey of a large group of radio-discovered MSPs for which no previous X-raypulsations have been detected and is therefore an unbiased survey of the X-rayproperties of radio-discovered MSPs. We find that only 47 Tuc D, O and R showsignificant pulsations at the >~ 4-sigma level, but there is statisticalevidence for rotational variability in five additional MSPs. Furthermore, weconstrain the pulsed magnetospheric emission of 7 more MSPs using Monte Carlosimulations. The result is that the majority of the 47 Tuc MSPs arecharacterized by low pulsed fractions, <~ 50%. In cases where larger pulsedfractions are measured the folded pulse profiles show relatively large dutycycles. When considered with previous spectroscopic studies, this suggests thatthe X-ray emission arises from the neutron star's heated polar caps, and insome cases, from intra-binary shocks, but generally not directly from thestar's magnetosphere. We discuss the impact of these results on ourunderstanding of high energy emission from MSPs.Comment: 21 pages, accepted for publication in Ap