Chandra X-ray Observations of 12 Millisecond Pulsars in the Globular Cluster M28

We present a Chandra X-ray Observatory investigation of the millisecond pulsars in the globular cluster M28 (NGC 6626). In what is one of the deepest X-ray observations of a globular cluster, we firmly detect seven and possibly detect two of the 12 known M28 pulsars. With the exception of PSRs B1821...

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Bibliographic Details
Published in:The Astrophysical journal 2011-04, Vol.730 (2), p.81
Main Authors: Bogdanov, Slavko, van den Berg, Maureen, Servillat, Mathieu, Heinke, Craig O, Grindlay, Jonathan E, Stairs, Ingrid H, Ransom, Scott M, Freire, Paulo C. C, Bégin, Steve, Becker, Werner
Format: Article
Language:English
Subjects:
Astronomy
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
COSMIC RADIO SOURCES
Earth, ocean, space
EMISSION
Exact sciences and technology
High Energy Astrophysical Phenomena
Physics
PULSARS
SPECTRA
STAR CLUSTERS
X-RAY SPECTRA
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Summary:We present a Chandra X-ray Observatory investigation of the millisecond pulsars in the globular cluster M28 (NGC 6626). In what is one of the deepest X-ray observations of a globular cluster, we firmly detect seven and possibly detect two of the 12 known M28 pulsars. With the exception of PSRs B1821-24 and J1824-2452H, the detected pulsars have relatively soft spectra, with X-ray luminosities 10{sup 30}-10{sup 31} erg s{sup -1} (0.3-8 keV), similar to most 'recycled' pulsars in 47 Tucanae and the field of the Galaxy, implying thermal emission from the pulsar magnetic polar caps. We present the most detailed X-ray spectrum to date of the energetic PSR B1821-24. It is well described by a purely non-thermal spectrum with spectral photon index {Gamma} = 1.23 and luminosity 1.4 x 10{sup 33}{Theta}(D/5.5 kpc){sup 2} erg s{sup -1} (0.3-8 keV), where {Theta} is the fraction of the sky covered by the X-ray emission beam(s). We find no evidence for the previously reported line emission feature around 3.3 keV, most likely as a consequence of improvements in instrument calibration. The X-ray spectrum and pulse profile of PSR B1821-24 suggest that the bulk of unpulsed emission from this pulsar is not of thermal origin, and is likely due to low-level non-thermal magnetospheric radiation, an unresolved pulsar wind nebula, and/or small-angle scattering of the pulsed X-rays by interstellar dust grains. The peculiar binary PSR J1824-2452H shows a relatively hard X-ray spectrum and possible variability at the binary period, indicative of an intrabinary shock formed by interaction between the relativistic pulsar wind and matter from its non-degenerate companion star.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/730/2/81