Central Bureau for Astronomical Telegrams
IAUC 7025: XTE J1550-564; V1333 Aql
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Circular No. 7025
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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XTE J1550-564
J. McClintock and G. Sobczak, Harvard-Smithsonian Center for
Astrophysics; R. Remillard, E. Morgan, and A. Levine, Massachusetts
Institute of Technology; C. Bailyn, Yale University; and J. Orosz,
Pennsylvania State University, communicate: "XTE J1550-564 was
observed with the RXTE PCA during the Sept. 19-20 x-ray flare
reported on IAUC 7019. The source intensity during the 3000-s
exposure was above 6 Crab. Fourier analysis of the lightcurve from
the full energy range of the PCA (effectively 2-30 keV in this
case) reveals a high-frequency quasiperiodic oscillation (QPO) at
183.6 Hz, with a width (FWHM) of 46 Hz and an rms amplitude of 0.45
percent of the mean x-ray flux. The statistical significance of
the feature is above 8 sigma. The QPO is not seen during other PCA
observations at lower flux. This is the third blackhole candidate
known to exhibit x-ray QPOs above 50 Hz, following the 67-Hz QPO in
GRS 1915+105 (Morgan et al. 1997, Ap.J. 482, 993) and the 298-Hz
QPO in GRO J1655-40 (Remillard et al. 1998,
http://xxx.lanl.gov/abs/astro-ph/?9806049). The QPO is likely to
be an effect of general relativity, with the QPO frequency
dependent on both the mass and spin of the accreting black hole,
but there are competing models for such oscillations. Meanwhile,
recent ASM and PCA observations made between Sept. 25 and Oct. 5
indicate intensities (2-12 keV) in the range of 1.2 to 1.4 Crab."
V1333 AQUILAE
S. A. Ilovaisky and C. Chevalier, Observatoire de Haute-
Provence (OHP), write: "The brightening of the optical counterpart
of the Aquila X-1 recurrent transient reported on IAUC 7017 did not
develop into an full-blown outburst. CCD photometry obtained with
the 1.2-m OHP telescope up until Oct. 3 shows that the source
remained at a low intensity level for about 10 days, and some time
after Sept. 24 it faded into quiescence, where it now remains.
During this brightening, the 18.95-hr modulation (IAUC 6806) was
detected with the expected phase and amplitude. We have observed
precursor events in 1995, 1996, and 1997 that preceded the main
outburst by about 2 months. If this latest event is such a
precursor, a normal outburst would be expected by early November."
(C) Copyright 1998 CBAT
1998 October 6 (7025) Daniel W. E. Green
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