Circular No. 4170 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION 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." NOTICE TO CONTRIBUTORS Starting Feb. 1, line charges are to be increased to $12.50 per line plus $35.00 per title ($25.00 for shared titles). Line charges are levied on all items relating to non-optical observations, and also to optical observations other than discovery announcements of comets, unusual minor planets, satellites, novae and supernovae and essential follow-up information: promptly- reported astrometric and--for novae and supernovae--spectroscopic (but not photometric) observations. Contributions by amateur astronomers, accepted as space permits, are exempt from charges. 1986 January 31 (4170) Brian G. Marsden
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