IAUC 4170: GX 3+1; Notice

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                                                  Circular No. 4170
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM    Telephone 617-495-7244/7440/7444

GX 3+1
     W. H. G. Lewin, Massachusetts Institute of Technology (MIT)
and Max-Planck-Institut fur Extraterrestrische Physik (MPIEP); J.
van Paradijs, University of Amsterdam; G. Hasinger, MPIEP; W. H.
Penninx, MIT; M. van der Klis, European Space Agency; F. Jansen,
Laboratory for Space Research, Leiden; and A. Langmeier, M. Sztajno
and J. Trumper, MPIEP, telex: "We observed the bright bulge source
GX 3+1 = 4U 1744-26 with EXOSAT during 1985 Sept. 4.159-4.900 UT
at a countrate between 700 and 870 cts s**-1 (0.14 m**2)-1 (this
corresponds to a flux level of ~ 1.2 x 10**-11 J m**-2 s**-1 in the energy
range 1-16 keV) and detected quasiperiodic oscillations (QPO), as
well as low-frequency noise (LFN, power-law slope 1.01 +/- 0.03).
The average power spectrum during Sept. 4.338-4.474 shows a peak
QPO with a centroid frequency of 8.6 +/- 0.9 Hz and a width (FWHM)
of 4.4 +/- 1.6 Hz.  The QPO peak is significant at a 4-sigma level of
confidence, which takes into account a number of five-trials (the
period during which we saw QPO is ~ one-fifth of the whole
observation). The integrated excess power in the peak corresponds to
an rms variation of 2.7 +/- 0.5 percent.  The excess power in the
LFN (integrated from 0.01 to 2 Hz) is strongly energy-dependent;
its rms variation corresponds to 1.5 +/- 0.2, 2.4 +/- 0.2 and 4.2 +/-
0.3 percent in the energy bands 0.9-3.1, 3.1-6.8 and 6.8-15.8 keV,
respectively (deadtime corrected, and assuming that the shape does
not depend on energy).  Small flux changes (10 percent) at low
energies (0.9-3.1 keV) were correlated with large (35 percent)
variations in hardness ratio (6.8-15.8 keV to 0.9-3.1 keV).  However,
there is no obvious relation between the presence of QPO and
spectral hardness.  This is the eighth bright, low-mass, x-ray
binary that shows the QPO/LFN phenomenon."

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1986 January 31                (4170)              Brian G. Marsden

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