Central Bureau for Astronomical Telegrams
IAUC 6320: 4U 1728-34; 29P
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Circular No. 6320
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)
4U 1728-34
T. Strohmayer and W. Zhang, Universities Space Research
Association (USRA) and the Laboratory for High Energy Astrophysics,
Goddard Space Flight Center (LHEA/GSFC); and J. Swank, LHEA/GSFC,
report the detection with the proportional counter array (PCA)
onboard the X-ray Timing Explorer (XTE) of very-high-frequency
variability in the quiescent x-ray intensity from the low-mass x-
ray binary 4U 1728-34: "Two features, perhaps distinct, are seen
in the power spectrum and appear to be correlated with the source
intensity. When the PCA source countrate is 1500-1800 counts/s, a
quasiperiodic oscillation (QPO) is seen with a centroid frequency
of 800 Hz, FWHM about 94 Hz, and fractional rms variation in the x-
ray intensity of 8.4 percent. This feature is accompanied by
strong, high-frequency noise extending up to 200 Hz. When the PCA
source countrate > 2100 counts/s, a much narrower power spectral
feature is seen at 740-800 Hz, with a FWHM of only 8 Hz. The
strength of this feature corresponds to a fractional rms variation
of about 5 percent. The high-frequency noise seen in the low-
countrate state is not present in the high-countrate state.
Preliminary searches with data sampled at 16 microseconds do not
reveal any additional significant features in the power spectrum
above 1 kHz. Analysis of data segments separated in time suggests
that the center frequencies of the features can vary by as much as
5-6 percent over several hours. To our knowledge, this represents
the highest-frequency time variability yet seen from a neutron-star
system. Explanations in terms of either keplerian frequencies or a
beat-frequency model cannot yet be ruled out, although no evidence
has yet been seen for a coherent pulsar frequency in the same data.
In addition, we note that oscillation modes associated with the
crust of a neutron star have frequencies in the range observed."
COMET 29P/SCHWASSMANN-WACHMANN 1
This comet appears to be in outburst, as indicated by the
following total magnitude estimates (visual unless otherwise noted):
Jan. 4.83 UT, 13.8 (Kojima, Chiyoda, Japan, 0.25-m reflector + CCD);
21.34, 13.2 (A. Hale, Cloudcroft, NM, 0.41-m reflector); Feb. 2.64,
14.2 (Kojima); 13.25, 12.6 (R. Keen, Mt. Thorodin, CO, 0.32-m
reflector; 2'.5 coma); 15.66, 13.3 (Kojima); 18.06, 13.8 (J.
Carvajal, Teruel, Spain, 0.44-m reflector); 19.54, 11.6 (Kojima;
strong, nearly stellar condensation with a faint coma extended
toward the northwest); 20.27, 11.8 (Hale; 0'.2 coma).
(C) Copyright 1996 CBAT
1996 February 20 (6320) Daniel W. E. Green
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