TY - JOUR
T1 - Discovery of kilohertz quasi-periodic oscillations in GX 17 + 2
AU - Wijnands, Rudy
AU - Homan, Jeroen
AU - Van Der Klis, Michiel
AU - Méndez, Mariano
AU - Kuulkers, Erik
AU - Van Paradijs, Jan
AU - Lewin, Walter H.G.
AU - Lamb, Frederick K.
AU - Psaltis, Dimitrios
AU - Vaughan, Brian
N1 - Funding Information:
This work was supported in part by the Netherlands Foundation for Research in Astronomy (ASTRON) grant 781-76-017 and by NSF grant AST 93-15133. B. V. (NAG 5-3340), F. K. L. (NAG 5-2925), J. v. P. (NAG 5-3269, NAG 5-3271), and W. H. G. L. acknowledge support from NASA grants. M. M. is a fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.
Publisher Copyright:
© 1997 The American Astronomical Society. All rights reserved.
PY - 1997/12/1
Y1 - 1997/12/1
N2 - We observed the low-mass X-ray binary and Z source GX 17 + 2 with the Rossi X-Ray Timing Explorer during 1997 February 6-8, April 1-4, and July 26-27. The X-ray color-color diagram shows a clear Z track. Two simultaneous kHz quasi-periodic oscillations (QPOs) are present in each observation, whose frequencies are well correlated with the position of the source on the Z track. At the left end of the horizontal branch (HB), only the higher frequency peak is observed, at 645 ± 9 Hz, with an rms amplitude of 5.7% ± 0.5% and an FWHM of 183 ± 35 Hz. When the source moves down the Z track to the upper normal branch, the frequency of the kHz QPO increases to 1087 ± 12 Hz, and the rms amplitude and FWHM decrease by a factor of 2. Farther down the Z track, the QPO becomes undetectable, with rms upper limits typically of 2.0%. Halfway down the HB, a second QPO appears in the power spectra with a frequency of 480 ± 23 Hz. The frequency of this QPO also increases when the source moves along the Z track, up to 781 ± 11 Hz halfway down the normal branch, while the rms amplitude and FWHM stay approximately constant at 2.5% and 70 Hz. The QPO frequency difference is constant at 293.5 ± 7.5 Hz. Simultaneously with the kHz QPOs, we detect HB QPOs (HBOs). The simultaneous presence of HBOs and kHz QPOs excludes the magnetospheric beat-frequency model as the explanation for at least one of these two phenomena.
AB - We observed the low-mass X-ray binary and Z source GX 17 + 2 with the Rossi X-Ray Timing Explorer during 1997 February 6-8, April 1-4, and July 26-27. The X-ray color-color diagram shows a clear Z track. Two simultaneous kHz quasi-periodic oscillations (QPOs) are present in each observation, whose frequencies are well correlated with the position of the source on the Z track. At the left end of the horizontal branch (HB), only the higher frequency peak is observed, at 645 ± 9 Hz, with an rms amplitude of 5.7% ± 0.5% and an FWHM of 183 ± 35 Hz. When the source moves down the Z track to the upper normal branch, the frequency of the kHz QPO increases to 1087 ± 12 Hz, and the rms amplitude and FWHM decrease by a factor of 2. Farther down the Z track, the QPO becomes undetectable, with rms upper limits typically of 2.0%. Halfway down the HB, a second QPO appears in the power spectra with a frequency of 480 ± 23 Hz. The frequency of this QPO also increases when the source moves along the Z track, up to 781 ± 11 Hz halfway down the normal branch, while the rms amplitude and FWHM stay approximately constant at 2.5% and 70 Hz. The QPO frequency difference is constant at 293.5 ± 7.5 Hz. Simultaneously with the kHz QPOs, we detect HB QPOs (HBOs). The simultaneous presence of HBOs and kHz QPOs excludes the magnetospheric beat-frequency model as the explanation for at least one of these two phenomena.
KW - Accretion, accretion disks
KW - Stars: individual (GX 1712)
KW - Stars: neutron
KW - X-rays: stars
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U2 - 10.1086/311039
DO - 10.1086/311039
M3 - Article
AN - SCOPUS:85033497402
SN - 2041-8205
VL - 490
SP - 1157
EP - 1160
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 2
ER -