IAUC 4068: V818 Sco; NGC 6212

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IAUC number

                                                  Circular No. 4068
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

     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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