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IAUC 7294: 1999em; XTE J1859+226

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                                                  Circular No. 7294
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)


SUPERNOVA 1999em IN NGC 1637
     W. D. Li, University of California at Berkeley, on behalf of
the Lick Observatory Supernova Search, report the discovery, on an
unfiltered CCD frame taken on Oct. 29.44 UT with the 0.8-m Katzman
Automatic Imaging Telescope, of a supernova (mag about 13.5)
located at R.A. = 4h41m27s.04, Decl. = -2 51'45".2 (equinox 2000.0),
which is 15".2 west and 25".1 north of the nucleus of NGC 1637.
SN 1999em was confirmed at the Beijing Astronomical Observatory on
Oct. 29.7.  A KAIT image of the same field on Oct. 20.45 showed
nothing at the position of SN 1999em (limiting mag about 19.0).


XTE J1859+226
     R. I. Hynes, Southampton University; and C. A. Haswell, A. J.
Norton, and S. Chaty, Open University, write:  "Following optical
and near-infrared monitoring of XTE J1859+226 (IAUC 7279, 7284),
Hubble Space Telescope (HST) STIS observations were performed on
Oct. 18.10-18.38 UT spanning 112-1026 nm.  The ultraviolet spectrum
shows broad (12 000 km/s FWZI) and deep Ly-alpha absorption, strong
C IV 155-nm emission (EW = 1.1 nm; 4000 km/s FWZI) and weaker
emission lines of C III, N V, O III, O IV, O V, Si IV, and He II.
Sharp absorption lines of Si II, Si III, Mg II, and other species
also appear with possible interstellar origin.  Preliminary
analysis of the 220-nm interstellar feature suggests E(B-V) = 0.58
+/- 0.07.  The dereddened optical spectral energy distribution can
be represented by a steep blue power law (spectral index +1.2),
flattening in the ultraviolet.  This resembles energy distributions
of other short-period soft-x-ray transients, suggesting that XTE
J1859+226 has a binary period < 1 day.  A 20-percent decline in
110-170-nm fluxes during the observation coincides with an x-ray
decline seen in RXTE/ASM lightcurves.  Shorter timescale variations
are present, but no persistent coherent modulation was detected.
Preliminary analyses of 33 hr of optical time-series data collected
between Oct. 13.86 and 20.24 at the Nordic Optical Telescope (J. E.
Solheim, R. Ostensen, T. M. C. Abbott), Braeside Observatory (R.
Fried, J. McFarland), the Jacobus Kapteyn Telescope (D. J. Rolfe,
D. A. Lott), Keele (Z. Ioannou), Mt. Laguna (A. Shafter), St.
Andrews (K. O'Brien, K. Horne), and Manastash Ridge Observatory (K.
Krisciunas), and also 2.5 hr of infrared time-series data at the
U.K. Infrared Telescope (R. J. Ivison) on Oct. 18.19-18.31,
suggests a 1-percent modulation with period 22-23 min.  Further HST
observations are scheduled for Nov. 6.82-6.93 and 19.43-19.55;
coordinated groundbased observations are encouraged."

                      (C) Copyright 1999 CBAT
1999 October 30                (7294)            Daniel W. E. Green

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