Central Bureau for Astronomical Telegrams
IAUC 6971: 1998cp; XTE J2123-058
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Circular No. 6971
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1998cp IN MCG +9-21-11
A. V. Filippenko and A. J. Barth, University of California at
Berkeley, report that a CCD spectrum obtained on July 17 UT with
the Shane 3-m reflector at Lick Observatory confirms that SN 1998cp
(cf. IAUC 6954) is indeed a supernova. However, the spectral
classification is uncertain; further processing of the data is
required.
XTE J2123-058
J. Casares, M. Serra-Ricart, C. Zurita, A. Gomez, and D.
Alcalde, Instituto de Astrofisica de Canarias; and P. Charles,
University of Oxford, report the discovery of optical eclipses in
the x-ray transient XTE J2123-058 (IAUC 6955): "R-band images were
obtained between July 2 and 12 with the European Space Agency's
Optical Ground Station 1-m telescope at the Observatorio del Teide.
Our light curves show triangular-shaped minima with a central depth
of 0.65 mag, repeating each night, indicating a periodicity of
roughly 1 day. The dips, which we interpret as eclipses of the
accretion disk by the companion star, have a total duration of 0.16
day. Preliminary analysis, using phase-dispersion minimization,
yields a strong peak at 1.99 days. After phase folding on this
period and submultiples of it, we favor an orbital period of 0.993
or 0.993/2 day. A provisional ephemeris for the time of mid-
eclipse is HJD 24451001.685(2) + 0.993(2)E. Observations at other
wavelengths (especially in x-rays) to monitor the decline are
strongly encouraged. Optical monitoring from widely-distributed
sites is particularly important to disentangle 1-day aliases and
search for the secondary minimum."
J. Homan, M. van der Klis, J. van Paradijs, and M. Mendez,
Astronomical Institute 'Anton Pannekoek', University of Amsterdam,
communicate: "We report the discovery, using RXTE PCA data from
July 14.4 to 14.8 UT, of two high-frequency quasiperiodic
oscillations (QPOs) in the persistent x-ray flux of the newly
discovered x-ray transient XTE J2123-058 (IAUC 6955). The QPOs
have frequencies of 855 +/- 5 and 1123 +/- 7 Hz, widths of 33.5 +/-
11.8 and 51.5 +/- 15.1 Hz, and rms amplitudes of 6.3 +/- 0.8 and
7.4 +/- 0.9 percent (2-11 keV). Both QPOs get stronger with photon
energy and are detected at count rates below about 640 counts/s
(2-60 keV, including background), but undetected above. Two x-ray
bursts were examined for oscillations, but none were found. We
recommend further RXTE observations when the PCA level drops below
about 640 counts/s."
(C) Copyright 1998 CBAT
1998 July 17 (6971) Daniel W. E. Green
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