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IAUC 6689: 1997cs; MXB 1730-335

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                                                 Circular No. 6689
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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     J. Mueller reports her discovery of a supernova (mag about 17)
on a IV-N plate taken on June 26 UT with the 1.2-m Oschin Schmidt
Telescope in the course of the second Palomar Sky Survey.  S. Jha,
P. Garnavich, P. Challis, and R. Kirshner, Harvard-Smithsonian
Center for Astrophysics, report that a spectrogram of SN 1997cs,
taken by D. Koranyi on June 30.29 UT at the Whipple Observatory
1.5-m telescope, shows this to be a type-IIn supernova with
moderately broad Balmer emission (1800 km/s FWHM), along with He I
emission at 587.5 and 706.5 nm.  Blended emission lines of
permitted Fe II are also visible.  The supernova is at redshift
0.037, based on emission lines of the host galaxy.  Images taken
concurrently by M. Gomez with the 1.2-m telescope yield magnitude V
= 17.4.  G. V. Williams provides the following precise position for
the supernova from one of the Gomez images:  R.A. = 15h13m39s.78,
Decl. = +2 53'44".5 (equinox 2000.0; uncertainty +/- 0".4); the
corresponding offset is 18".1 east and 1".2 north of the galaxy's

MXB 1730-335
     R. Guerriero, W. H. G. Lewin, and J. Kommers, Massachusetts
Institute of Technology, report:  "Following detection of the rapid
burster MXB 1730-335 with the RXTE's All-Sky Monitor, we observed
the source on June 26.19 and 26.33 UT for 1500 and 2300 s,
respectively, with the RXTE PCA.  A persistent emission level of
4100 +/- 300 counts/s (total PCA countrate, 2-60 keV; 1 Crab =
13 500 counts/s) was inferred for the rapid burster, after
subtracting a contribution of 1200 +/- 200 counts/s from 4U 1728-34.
Seven type-II bursts were detected, with peak countrates of
1100-2900 counts/s above the persistent emission.  The bursts had a
10-20-s smooth rise and a 40-60-s decay, and occurred 450-650 s
apart.  Type-I bursts show a characteristic spectral softening
during burst decay, which was not present in any of these bursts.
The spectral hardness ratios during bursts showed little variation
from those of the persistent emission.  A preliminary analysis of
fourier power spectra shows no significant coherent or
quasiperiodic oscillations between 1 and 2048 Hz in the bursts or
persistent emission.  Upper limits (95-percent confidence) on the
strength of any narrow features in the power spectra are 3.4-
percent rms.  This active phase followed the previous one by 7
months (IAUC 6506).  Infrared and radio observations are
encouraged, particularly if coordinated with the ongoing public
RXTE PCA observations."

                      (C) Copyright 1997 CBAT
1997 June 30                   (6689)            Daniel W. E. Green

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