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Title: CHANDRA X-RAY OBSERVATIONS OF 12 MILLISECOND PULSARS IN THE GLOBULAR CLUSTER M28

Abstract

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, andmore » 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.« less

Authors:
 [1]; ; ;  [2];  [3]; ;  [4];  [5];  [6];  [7]
  1. Department of Physics, McGill University, 3600 University Street, Montreal, QC H3A 2T8 (Canada)
  2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  3. Department of Physics, University of Alberta, 11322 89 Avenue, Edmonton, AB T6G 2G7 (Canada)
  4. Department of Physics, University of British Columbia, 6224 Agricultural Road Vancouver, BC V6T 1Z1 (Canada)
  5. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22901 (United States)
  6. Max-Planck-Institut fuer Radio Astronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)
  7. Max-Planck-Institut fuer Extraterrestrische Physik, D-85740 Garching bei Muenchen (Germany)
Publication Date:
OSTI Identifier:
21574871
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 730; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/730/2/81; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EMISSION; PULSARS; STAR CLUSTERS; X-RAY SPECTRA; COSMIC RADIO SOURCES; SPECTRA

Citation Formats

Bogdanov, Slavko, Van den Berg, Maureen, Servillat, Mathieu, Grindlay, Jonathan E, Heinke, Craig O, Stairs, Ingrid H, Begin, Steve, Ransom, Scott M, Freire, Paulo C. C., and Becker, Werner. CHANDRA X-RAY OBSERVATIONS OF 12 MILLISECOND PULSARS IN THE GLOBULAR CLUSTER M28. United States: N. p., 2011. Web. doi:10.1088/0004-637X/730/2/81.
Bogdanov, Slavko, Van den Berg, Maureen, Servillat, Mathieu, Grindlay, Jonathan E, Heinke, Craig O, Stairs, Ingrid H, Begin, Steve, Ransom, Scott M, Freire, Paulo C. C., & Becker, Werner. CHANDRA X-RAY OBSERVATIONS OF 12 MILLISECOND PULSARS IN THE GLOBULAR CLUSTER M28. United States. doi:10.1088/0004-637X/730/2/81.
Bogdanov, Slavko, Van den Berg, Maureen, Servillat, Mathieu, Grindlay, Jonathan E, Heinke, Craig O, Stairs, Ingrid H, Begin, Steve, Ransom, Scott M, Freire, Paulo C. C., and Becker, Werner. Fri . "CHANDRA X-RAY OBSERVATIONS OF 12 MILLISECOND PULSARS IN THE GLOBULAR CLUSTER M28". United States. doi:10.1088/0004-637X/730/2/81.
@article{osti_21574871,
title = {CHANDRA X-RAY OBSERVATIONS OF 12 MILLISECOND PULSARS IN THE GLOBULAR CLUSTER M28},
author = {Bogdanov, Slavko and Van den Berg, Maureen and Servillat, Mathieu and Grindlay, Jonathan E and Heinke, Craig O and Stairs, Ingrid H and Begin, Steve and Ransom, Scott M and Freire, Paulo C. C. and Becker, Werner},
abstractNote = {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.},
doi = {10.1088/0004-637X/730/2/81},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 730,
place = {United States},
year = {2011},
month = {4}
}