Central Bureau for Astronomical Telegrams
IAUC 6964: 1998ct; XTE J1748-288; C/1998 K1
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Circular No. 6964
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1998ct IN UGC 10062
S. Jha, P. Garnavich, P. Challis, and R. Kirshner, Harvard-
Smithsonian Center for Astrophysics, report that spectra of SN
1998ct (cf. IAUC 6957) were obtained by K. Rines and P. Berlind on
July 1.2 and 2.2 UT, respectively, with the F. L. Whipple
Observatory (FLWO) 1.5-m telescope. The spectra feature a blue
continuum with He I (587.5 nm) emission, and narrow H-alpha
emission (FWHM 450 km/s) on top of broader H-alpha emission (FWHM
8500 km/s), indicating that this supernova is of type IIn at an
early epoch. Images taken by P. Barmby with the FLWO 1.2-m
telescope on July 2.2 yield estimated magnitudes B = 17.4 and V =
17.1.
XTE J1748-288
D. Fox and W. Lewin, Massachusetts Institute of Technology,
report on behalf of a large collaboration: "We have examined the
Rossi X-ray Timing Explorer June 6.4 UT observation of the x-ray
and radio transient source XTE J1748-288 (IAUC 6932, 6934, 6937,
6938); the count rate of the source at this time was about 5100
counts/s in the Proportional Counter Array (2-60 keV). The power-
density spectrum shows two quasi-periodic oscillation (QPO) peaks,
at about 0.5 and 32 Hz respectively, superposed on a 5.8-percent-
r.m.s. (0-100 Hz) 'double flat-top/power law' noise spectrum with a
-2.2 power-law slope between 1.6 and 2.0 Hz and above a 5.9-Hz
break frequency. The 0.5-Hz QPO moves from 0.35 to 0.50 Hz and
strengthens over the course of the 2700-s observation; its FWHM is
about 0.5 Hz and its average r.m.s. strength is 3.4 percent. The
32-Hz QPO, by contrast, is relatively stationary, with a FWHM of
5.4 Hz and an r.m.s. strength of 3.3 percent. The x-ray colors of
the source (2.0-4.6:4.6-9.4:9.4-18.3-keV counts ratio of 3.2:4.1:1)
are typical for black-hole candidates in the 'low state', and in
particular this source's spectral and timing properties are
reminiscent of low- or very-high-state behavior in GX 339-4."
COMET C/1998 K1 (MUELLER)
Total visual magnitude estimates: May 19.90 UT, 14.8 (M.
Lehky, Hradec Kralove, Czech Republic, 0.42-m reflector); 26.89,
14.4 (K. Hornoch, Lelekovice, Czech Republic, 0.35-m reflector);
31.88, 14.9 (Lehky); June 20.89, 14.8 (Lehky); 21.91, 14.6
(Lehky); 25.90, 14.7 (Lehky).
(C) Copyright 1998 CBAT
1998 July 2 (6964) Daniel W. E. Green
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