CHANDRA X-RAY OBSERVATIONS OF 12 MILLISECOND PULSARS IN THE GLOBULAR CLUSTER M28
- Department of Physics, McGill University, 3600 University Street, Montreal, QC H3A 2T8 (Canada)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Physics, University of Alberta, 11322 89 Avenue, Edmonton, AB T6G 2G7 (Canada)
- Department of Physics, University of British Columbia, 6224 Agricultural Road Vancouver, BC V6T 1Z1 (Canada)
- National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22901 (United States)
- Max-Planck-Institut fuer Radio Astronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)
- Max-Planck-Institut fuer Extraterrestrische Physik, D-85740 Garching bei Muenchen (Germany)
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.
- OSTI ID:
- 21574871
- Journal Information:
- Astrophysical Journal, Vol. 730, Issue 2; Other Information: DOI: 10.1088/0004-637X/730/2/81; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Broadband pulsations from PSR B1821-24: Implications for emission models and the pulsar population of M28
Broadband pulsations from PSR B1821–24: Implications for emission models and the pulsar population of M28