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IAUC 7402: 2000bk; SMC X-2; UX Ant

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                                                  Circular No. 7402
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2000bk IN NGC 4520
     Mark Armstrong, Rolvenden, Kent, England, reports his
discovery of an apparent supernova (mag 17) visible on four CCD
images taken between Apr. 11.942 and 12.090 UT.  SN 2000bk is
located at R.A. = 12h33m53s.94, Decl. = -7 22'42".9 (equinox
2000.0; mean of measurements from four frames), which is 61" east
and 10" south of the nucleus of NGC 4520.  Earlier images taken by
Armstrong on Jan. 10 and Mar. 4-5 show nothing at this position
(limiting mag 18), neither is anything visible on the IIIa-J SERC J
survey image taken on 1983 Apr. 15 (limiting mag 23) or on the
IIIa-F Palomar Sky Survey plate taken on 1993 Feb. 23 (limiting mag
     W. Li, University of California at Berkeley, reports that a
prediscovery image of SN 2000bk was obtained with the 0.8-m Katzman
Automatic Imaging Telescope on Apr. 7.3 UT, showing the new object
at mag about 17.0.

     R. Corbet, Goddard Space Flight Center (GSFC) and Universities
Space Research Association; and F. E. Marshall, GSFC, report on
behalf of the RXTE teams at GSFC and the Massachusetts Institute of
Technology:  "We have discovered pulsed x-ray emission from a
position consistent with the location of SMC X-2.  RXTE ASM
observations indicate activity since the middle of January with a
mean flux of about 10 mCrab.  Slews with the PCA over SMC X-2 on
Apr. 9 and 12 show a source at R.A. = 0h54m53s, Decl. = -73o38',
with a 90-percent-confidence error circle of 3' radius and a 2-10-
keV flux of about 3 mCrab.  A pointed PCA observation on Apr. 12
shows pulsations at a period of 2.374 +/- 0.007 s with a pulsed
fraction of about 30 percent.  Imaging x-ray observations, and
observations of the suggested optical counterpart (Murdin et al.
1979, MNRAS 186, 43P), are encouraged."

     P. Williams, Heathcote, New South Wales, reports that this R
CrB-type star appears to be fading from its normal visual mag 12.0,
as indicated by his own visual magnitude estimates:  Mar. 1.475 UT,
12.0; 3.450, 12.0; 31.473, 12.1; Apr. 11.434, 12.5; 13.534, 12.9.
Williams adds that this is the first recorded fade of UX Ant since
that reported in June/July 1990 (cf. IAUC 5058, 5089).

                      (C) Copyright 2000 CBAT
2000 April 14                  (7402)            Daniel W. E. Green

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