Variability of Nineteen Millisecond Pulsars in 47 Tucanae with CHANDRA/HRC-S

Abstract

We present results from our 830 ksec observation of the globular cluster 47 Tucanae with the Chandra X-ray Observatory's High Resolution Camera-S. We limit our analysis here to the 19 previously known, localized millisecond pulsars (MSPs) in the cluster. This work more than doubles the sample of X-ray-detected MSPs observed with sensitivity to rotational variability; it is also the first survey of a large group of radio-discovered MSPs for which no previous X-ray pulsations have been detected and is therefore an unbiased survey of the X-ray properties of radio-discovered MSPs. We find that only 47 Tuc D, O and R show significant pulsations at the >~ 4-sigma level, but there is statistical evidence for rotational variability in five additional MSPs. Furthermore, we constrain the pulsed magnetospheric emission of 7 more MSPs using Monte Carlo simulations. The result is that the majority of the 47 Tuc MSPs are characterized by low pulsed fractions, <~ 50%. In cases where larger pulsed fractions are measured the folded pulse profiles show relatively large duty cycles. When considered with previous spectroscopic studies, this suggests that the X-ray emission arises from the neutron star's heated polar caps, and in some cases, from intra-binary shocks, but generally not directly from the star's magnetosphere. We discuss the impact of these results on our understanding of high energy emission from MSPs.

21 pages, accepted for publication in ApJ

References in corpus (2)

• Chandra X-Ray Observations of Nineteen Millisecond Pulsars in the Globular Cluster 47 Tucanae
• GBT Discovery of Two Binary Millisecond Pulsars in the Globular Cluster M30

Cited by in corpus (14)

• The long-term evolution of the spin, pulse shape, and orbit of the accretion-powered millisecond pulsar SAX J1808.4-3658
• Constraints on Neutron Star Properties from X-ray Observations of Millisecond Pulsars
• The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9
• Thermal X-rays from Millisecond Pulsars: Constraining the Fundamental Properties of Neutron Stars
• NICER X-ray Observations of Seven Nearby Rotation-Powered Millisecond Pulsars
• Chandra X-ray Observations of 12 Millisecond Pulsars in the Globular Cluster M28
• Discovery of an Isolated Compact Object at High Galactic Latitude
• Chandra and Swift Follow-up Observations of the Intermediate Mass Black Hole in ESO243-49
• The Discovery of a Very Faint X-ray Transient in the Globular Cluster M15
• X-ray and $\gamma$-ray Studies of the Millisecond Pulsar and Possible X-ray Binary/Radio Pulsar Transition Object PSR J1723-2837
• H.E.S.S. upper limit on the very high energy gamma-ray emission from the globular cluster 47 Tucanae
• The impact of surface temperature inhomogeneities on quiescent neutron star radius measurements
• On the vanishing orbital X-ray variability of the eclipsing binary millisecond pulsar 47 Tuc W
• Spectral analysis of the quiescent low-mass X-ray binary in the globular cluster M30