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IAUC 7114: 1999ac; XTE J1550-564

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                                                  Circular No. 7114
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)

SUPERNOVA 1999ac IN NGC 6063
     M. Modjaz, J. Y. King, M. Papenkova, A. Friedman, R. A.
Johnson, W. D. Li, R. R. Treffers, and A. V. Filippenko, University
of California at Berkeley, report their discovery of an apparent
supernova in NGC 6063 during the course of the Lick Observatory
Supernova Search with the 0.8-m Katzman Automatic Imaging Telescope
(KAIT).  SN 1999ac was discovered and confirmed on unfiltered
observations taken on Feb. 26.5 (mag about 15.2) and 27.5 UT (mag
about 15.0).  The new object is located at R.A. = 16h07m15s.01,
Decl. = +7o58'20".4 (equinox 2000.0), which is about 23".9 east and
29".8 south of the nucleus of NGC 6063.  KAIT images of the same
field on 1999 Feb. 20.5 (limiting mag about 17.5) and 1998 July
21.2 (limiting mag about 19.0) show nothing at the position of the

XTE J1550-564
     R. Jain and C. Bailyn, Yale University; J. McClintock and G.
Sobczak, Harvard-Smithsonian Center for Astrophysics; R. Remillard,
Massachusetts Institute of Technology; and J. Orosz, Pennsylvania
State University, report YALO consortium observations of XTE
J1550-564:  "We have obtained B-, V-, and I-band images virtually
every night since Jan. 4.3 UT and most recently covering 3.5 hr of
elapsed time per night.  We find that, between Jan. 4.3 and 22.3,
the source was steady at V = 16.04, B = 17.48, and I = 14.15.  Then
on Jan. 22.3, there was a 0.3-mag dip in the B, V, and I
magnitudes.  The source then remained steady, with a slight decline
to a new level (V = 16.17, B = 17.62, I = 14.29) until Feb. 6.3,
when another small dip (0.2 mag in I) occurred.  This was followed
by another period of steady slow decline.  Most recently, a much
larger decrease in optical brightness has occurred:  since Feb. 21,
the source has declined by > 0.5 magnitudes in B, V, and I.  RXTE
PCA observations show that the 2-20-keV x-ray flux increased from
6.5 x 10E-8 erg cmE-2 sE-1 on Feb. 21.5 to 7.4 x 10E-8 erg cmE-2
sE-1 on Feb. 23.9.  The x-ray spectrum from 2 to 20 keV is
dominated by the disk component, but the change in optical
intensity has been accompanied by a factor of two increase in the
power-law component of the x-ray flux from Feb. 21.5 to 23.9.  We
will continue to monitor this object on a daily basis for the
foreseeable future, and we strongly encourage other observations,
particularly of optical spectroscopy, to follow the current change
in state of this source."

                      (C) Copyright 1999 CBAT
1999 February 27               (7114)            Daniel W. E. Green

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