Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar PSR B1821-24

Werner Becker, Douglas A. Swartz, George G. Pavlov, Ronald F. Elsner, Jonathan Grindlay, Roberto Mignani, Allyn F. Tennant, Don Backer, Luigi Pulone, Vincenzo Testa, Martin C. Weisskopf

Research output: Contribution to journalArticle

78 Citations (Scopus)

Abstract

We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources, of which 12 lie within 1 core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources, for which we determine the X-ray luminosity function down to a limit of about 6 × 1030 ergs s-1. We measure the radial distribution of the X-ray sources and fit it to a King profile finding a core radius of rc,X ≈ 11″ We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05 ms pulsar B1821-24 and find that it is best described by a power law with photon index Γ ≃ 1.2. We find marginal evidence of an emission line centered at 3.3 keV in the pulsar spectrum, which could be interpreted as cyclotron emission from a corona above the pulsar's polar cap if the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.5-8.0 keV band is ≈ 3.5 × 10-13 ergs s -1 cm-2. We present spectral analyses of the five brightest unidentified sources. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature Teff = 90-10+30 eV and the radius RNS = 14.5-3.8+6.9 km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core. Using the Chandra-derived positions, we also report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.

Original languageEnglish (US)
Pages (from-to)798-811
Number of pages14
JournalAstrophysical Journal
Volume594
Issue number2 I
DOIs
StatePublished - Sep 10 2003

Fingerprint

globular clusters
pulsars
observatories
observatory
x rays
erg
neutron stars
radii
polar caps
Hubble Space Telescope
radial distribution
coronas
corona
cyclotrons
power law
luminosity
hydrogen
dipoles
magnetic field
atmospheres

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Becker, W., Swartz, D. A., Pavlov, G. G., Elsner, R. F., Grindlay, J., Mignani, R., ... Weisskopf, M. C. (2003). Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar PSR B1821-24. Astrophysical Journal, 594(2 I), 798-811. https://doi.org/10.1086/376967
Becker, Werner ; Swartz, Douglas A. ; Pavlov, George G. ; Elsner, Ronald F. ; Grindlay, Jonathan ; Mignani, Roberto ; Tennant, Allyn F. ; Backer, Don ; Pulone, Luigi ; Testa, Vincenzo ; Weisskopf, Martin C. / Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar PSR B1821-24. In: Astrophysical Journal. 2003 ; Vol. 594, No. 2 I. pp. 798-811.
@article{ffce8a85c099464c836e96d3a71cc430,
title = "Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar PSR B1821-24",
abstract = "We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources, of which 12 lie within 1 core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources, for which we determine the X-ray luminosity function down to a limit of about 6 × 1030 ergs s-1. We measure the radial distribution of the X-ray sources and fit it to a King profile finding a core radius of rc,X ≈ 11″ We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05 ms pulsar B1821-24 and find that it is best described by a power law with photon index Γ ≃ 1.2. We find marginal evidence of an emission line centered at 3.3 keV in the pulsar spectrum, which could be interpreted as cyclotron emission from a corona above the pulsar's polar cap if the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.5-8.0 keV band is ≈ 3.5 × 10-13 ergs s -1 cm-2. We present spectral analyses of the five brightest unidentified sources. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature Teff∞ = 90-10+30 eV and the radius RNS∞ = 14.5-3.8+6.9 km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core. Using the Chandra-derived positions, we also report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.",
author = "Werner Becker and Swartz, {Douglas A.} and Pavlov, {George G.} and Elsner, {Ronald F.} and Jonathan Grindlay and Roberto Mignani and Tennant, {Allyn F.} and Don Backer and Luigi Pulone and Vincenzo Testa and Weisskopf, {Martin C.}",
year = "2003",
month = "9",
day = "10",
doi = "10.1086/376967",
language = "English (US)",
volume = "594",
pages = "798--811",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2 I",

}

Becker, W, Swartz, DA, Pavlov, GG, Elsner, RF, Grindlay, J, Mignani, R, Tennant, AF, Backer, D, Pulone, L, Testa, V & Weisskopf, MC 2003, 'Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar PSR B1821-24', Astrophysical Journal, vol. 594, no. 2 I, pp. 798-811. https://doi.org/10.1086/376967

Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar PSR B1821-24. / Becker, Werner; Swartz, Douglas A.; Pavlov, George G.; Elsner, Ronald F.; Grindlay, Jonathan; Mignani, Roberto; Tennant, Allyn F.; Backer, Don; Pulone, Luigi; Testa, Vincenzo; Weisskopf, Martin C.

In: Astrophysical Journal, Vol. 594, No. 2 I, 10.09.2003, p. 798-811.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar PSR B1821-24

AU - Becker, Werner

AU - Swartz, Douglas A.

AU - Pavlov, George G.

AU - Elsner, Ronald F.

AU - Grindlay, Jonathan

AU - Mignani, Roberto

AU - Tennant, Allyn F.

AU - Backer, Don

AU - Pulone, Luigi

AU - Testa, Vincenzo

AU - Weisskopf, Martin C.

PY - 2003/9/10

Y1 - 2003/9/10

N2 - We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources, of which 12 lie within 1 core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources, for which we determine the X-ray luminosity function down to a limit of about 6 × 1030 ergs s-1. We measure the radial distribution of the X-ray sources and fit it to a King profile finding a core radius of rc,X ≈ 11″ We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05 ms pulsar B1821-24 and find that it is best described by a power law with photon index Γ ≃ 1.2. We find marginal evidence of an emission line centered at 3.3 keV in the pulsar spectrum, which could be interpreted as cyclotron emission from a corona above the pulsar's polar cap if the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.5-8.0 keV band is ≈ 3.5 × 10-13 ergs s -1 cm-2. We present spectral analyses of the five brightest unidentified sources. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature Teff∞ = 90-10+30 eV and the radius RNS∞ = 14.5-3.8+6.9 km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core. Using the Chandra-derived positions, we also report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.

AB - We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources, of which 12 lie within 1 core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources, for which we determine the X-ray luminosity function down to a limit of about 6 × 1030 ergs s-1. We measure the radial distribution of the X-ray sources and fit it to a King profile finding a core radius of rc,X ≈ 11″ We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05 ms pulsar B1821-24 and find that it is best described by a power law with photon index Γ ≃ 1.2. We find marginal evidence of an emission line centered at 3.3 keV in the pulsar spectrum, which could be interpreted as cyclotron emission from a corona above the pulsar's polar cap if the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.5-8.0 keV band is ≈ 3.5 × 10-13 ergs s -1 cm-2. We present spectral analyses of the five brightest unidentified sources. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature Teff∞ = 90-10+30 eV and the radius RNS∞ = 14.5-3.8+6.9 km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core. Using the Chandra-derived positions, we also report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.

UR - http://www.scopus.com/inward/record.url?scp=0242508389&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0242508389&partnerID=8YFLogxK

U2 - 10.1086/376967

DO - 10.1086/376967

M3 - Article

AN - SCOPUS:0242508389

VL - 594

SP - 798

EP - 811

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 I

ER -