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IAUC 7400: XTE J1550-564; 1999el

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                                                  Circular No. 7400
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)
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Phone 617-495-7244/7440/7444 (for emergency use only)


XTE J1550-564
     M. L. McCollough, Universities Space Research Association and
Marshall Space Flight Center (MSFC); C. A. Wilson, NASA/MSFC; and
X. Sun, University of Alabama in Huntsville, report for the Compton
Gamma Ray Observatory (CGRO) BATSE team:  "XTE J1550-564 (IAUC
7008, 7010) was detected in outburst with BATSE in the band 20-300
keV on Apr. 6 at a flux of 0.5 Crab (1.0 x 10**-8 erg cm**-2 s**-1)
and had risen to 0.6 Crab (1.2 x 10**-8 erg cm**-2 s**-1) on Apr. 8.
XTE J1550-564 is clearly being detected up to 300 keV.  The date
that this outburst began is uncertain because XTE J1550-564 was
unobservable with CGRO/BATSE from Mar. 26 to Apr. 5.  The
CGRO/BATSE light curve shows evidence for variability on time
scales of less than a day.  The energy spectrum for XTE J1550-564
can be fitted by a bremsstrahlung spectrum with a temperature of
101 +/- 8 keV or a broken power law with a break energy of 76 +/-
25 keV, a lower energy photon index of -1.4 +/- 0.4, and a high
energy photon index of -2.4 +/- 0.4."
     R. Jain and C. Bailyn, Yale University, report YALO consortium
observations of the optical counterpart of XTE J1550-564 using the
Yale 1-m telescope (+  ANDICAM instrument) at Cerro Tololo
Interamerican Observatory: "XTE J1550-564 has entered a new optical
outburst.  By Mar. 24.4 UT, the object was at V = 21.0,
significantly brighter than any of our 12 observations obtained
during the period Feb. 28-Mar. 17 (in all of which the source was
fainter than V = 21.4).  On Mar. 29.3, we find V = 19.07 +/- 0.03,
and on Apr. 6.3, V = 18.24 +/- 0.03.  The rate of brightening has
decreased in the past two days to V = 18.09 +/- 0.02 and 18.06 +/-
0.02 on Apr. 9.4 and 10.4, respectively.  Further observations at
other wavelengths are encouraged."


SUPERNOVA 1999el IN NGC 6951
     CCD magnitudes, unfiltered unless otherwise noted:  1999 Nov.
5.503 UT, 14.5 (S. Yoshida and K. Kadota, Ageo, Saitama, Japan);
13.484, 14.8 (Yoshida and Kadota); 2000 Jan. 28.740, R = 17.3 +/-
0.2 (L. Kiss, K. Sarneczky, and K. Sziladi, Piszkesteto, Hungary);
28.816, 16.7 (Yoshida and Kadota); Mar. 16.11, 17.7 +/- 0.2
(Sarneczky, Sziladi, and Kiss).

                      (C) Copyright 2000 CBAT
2000 April 10                  (7400)            Daniel W. E. Green

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