Central Bureau for Astronomical Telegrams
IAUC 6319: Sco X-1
The following International Astronomical Union Circular may be linked-to from your own Web pages, but must not otherwise be redistributed (see these notes on the conditions under which circulars are made available on our WWW site).
Read IAUC 6320
.dvi or
.ps format.
Circular No. 6319
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
SCORPIUS X-1
M. van der Klis, Astronomical Institute 'Anton Pannekoek',
University of Amsterdam; J. Swank, W. Zhang, and K. Jahoda, Goddard
Space Flight Center, NASA; E. Morgan and W. Lewin, Massachusetts
Institute of Technology; B. Vaughan, California Institute of
Technology; and J. van Paradijs, University of Alabama at
Huntsville and University of Amsterdam, report: "We have observed
quasiperiodic oscillations (QPOs) with frequencies between 1060 and
1130 Hz in two different 2- to 60-keV observations of Sco X-1 with
the X-ray Timing Explorer satellite. In the first observation, on
Feb. 14.470-14.492 UT, Sco X-1 was mostly in the lower normal
branch of the Z track in the x-ray color-color diagram, with clear
6- to 7-Hz, normal-branch QPOs. Power spectra of two simultaneous,
statistically-independent time series (resolution 16 and 62.5
microseconds, respectively) show a narrow QPO peak at 1062 +/- 7
and 1077 +/- 8 Hz, respectively, with a FWHM of about 60 Hz and a
deadtime-corrected, fractional, rms amplitude, r, of 0.74 +/- 0.10
percent. In the second observation, on Feb. 18.203-18.234, Sco X-1
changed state several times, moving along the Z track between the
lower normal and flaring branches, showing 7- and 16-Hz QPOs,
respectively. Using 250-microsecond data, a very narrow QPO peak
is seen in the normal branch at 1089.1 +/- 0.5 Hz with FWHM 15 +/-
3 Hz and r = 0.72 +/- 0.06 percent. In the flaring branch, the
peak is at 1133 +/- 7 Hz, FWHM is roughly 40 Hz, and r = 0.49 +/-
0.09 percent. In another segment of the same observation, 16- and
62-microsecond data taken in the normal branch again show similar
high-frequency, comparatively-narrow peaks. All peak significances
are between 3.5 and 4.5 sigma (single trial). In both observations,
there is evidence that the QPOs increase in frequency along the
normal branch and into the flaring branch (i.e., with mass-transfer
rate), and that part of the observed peak widths is due to this
motion. In a third observation, when Sco X-1 was in the flaring
branch, no significant kHz peak was seen. This is the fastest QPO
yet seen in an accreting compact object. The high-QPO frequency,
and its increase with mass-transfer rate, suggest that we may be
seeing the keplerian frequency at the inner edge of the disk near
the magnetospheric boundary, or its beat frequency with a slower
(about 100 Hz) pulsar. The fact that the high-frequency QPOs have
a similar dependence of strength and frequency on mass-transfer
rate as the well-known 6- to 20-Hz QPOs in Sco X-1 indicates that
the two phenomena might be related."
(C) Copyright 1996 CBAT
1996 February 20 (6319) Daniel W. E. Green
Read IAUC 6320
.dvi or
.ps format.
Our Web policy. Index to the CBAT/MPC/ICQ pages.
