Circular No. 4068 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 V818 SCORPII M. van der Klis, Space Science Department, European Space Agency, Noordwijk; F. Jansen, Space Research Laboratory, Leiden; N. White and L. Stella, EXOSAT Observatory, Darmstadt; and A. Peacock, Space Science Department, ESA, Noordwijk, communicate: "EXOSAT 5- to-35-keV data on V818 Sco = Sco X-1 with 8-ms time resolution between 1983 Aug. 29.96 and 30.48 UT show intensity-dependent quasiperiodic oscillations similar to GX 5-1 (cf. van der Klis et al., IAUC 4043). Like Middleditch and Priedhorsky (IAUC 4060), we observe a broad peak in the power spectrum when the source is not flaring. In our case, the peak is variable in width (2-10 Hz FWHM), strength (excess power equivalent to 1-3 percent sinusoidal modulation), and centroid frequency, f (7-17 Hz, all values from fitting a Lorentzian to the peak). The red noise which is present in the data is strongest when the source is bright and the quasi- oscillations are absent. Initially, when the source is only quiescent during 10- to 20-min intervals between flaring episodes, f is strongly correlated to source flux, increasing from 10-17 Hz for a 13 percent rise in flux. If the beat-frequency model proposed for GX 5-1 by Alpar and Shaham (IAUC 4046; also Alpar and Shaham, and Alpar et al., to appear in Nature) applies to this part of our data, then we derive a neutron-star spin frequency of about 100 Hz and a magnetospheric radius of about 70 km -- values remarkably similar to GX 5-1 (van der Klis et al., submitted to Nature). However, during the transition to an extended low state, starting at about Aug. 30.42 (White et al., Ap. J., in press), when the peak is seen continuously, f varies apparently erratically between 7-11 Hz for flux variations over the same range as before. This behavior (and that of the red noise) is in apparent contradiction with the proposed model." NGC 6212 G. Kriss, Department of Astronomy, University of Michigan, writes: "Optical spectroscopy of the active nucleus of the elliptical galaxy NGC 6212 (IAUC 4060) obtained with the photon-counting intensified Reticon spectrometer on the McGraw-Hill 1.3-m telescope on May 22.3 UT reveals broad H-alpha emission at a redshift of 0.03. No other emission lines are visible from 390.0 nm to 750.0 nm, and starlight dominates the continuum. The apparently steep Balmer decrement and the continuum dominated by starlight are typical of many low-redshift, x-ray selected active galactic nuclei." 1985 May 28 (4068) Daniel W. E. Green
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