Central Bureau for Astronomical Telegrams
IAUC 7121: N SMC; XTE J1550-564
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Circular No. 7121
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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Phone 617-495-7244/7440/7444 (for emergency use only)
NOVA IN THE SMALL MAGELLANIC CLOUD
D. L. Welch, McMaster University, and the MACHO collaboration
(cf. IAUC 6312) report their discovery of an apparent nova at R.A.
= 1h02m21s.8, Decl. = -73o18'27" (equinox 2000.0), which peaked in
brightness sometime between consecutive observations on 1998 Dec.
25.513 (V = 19.0) and 1999 Jan. 3.519 UT (V < 13.5; image
saturated). Prior to eruption, a stellar object at the nova's
position had a mean magnitude of V = 19.0, with peak-to-peak
brightness changes of 0.5 mag on a timescale of hundreds of days.
On 1999 Mar. 3.463, it was at V about 16, and it continues to fade.
XTE J1550-564
J. Homan, R. Wijnands, and M. van der Klis, Astronomical
Institute 'Anton Pannekoek', University of Amsterdam, report: "The
blackhole candidate x-ray transient source XTE J1550-564 (IAUC
7008) seems to have undergone a sudden major state transition. The
source was observed with the RXTE PCA instrument on Mar. 4.80 UT.
The source flux (2-20.0 keV) was 6.0 x 10E-8 erg sE-1 cmE-2. A
quasiperiodic oscillation (QPO) was detected at 284.2 +/- 1.3 Hz,
with a width (FWHM) of 29 +/- 4 Hz and an rms amplitude of 3.9 +/-
0.2 percent (6.4-60 keV; 11.5 sigma). The QPO amplitudes in the
energy ranges 2-60, 2-6.4, 6.4-13, and 13-60 keV, are 1.3 +/- 0.2,
< 0.8, 3.2 +/- 0.2, and 8.4 +/- 0.9 percent, respectively. This
high-frequency QPO is most likely related to the 184-Hz QPO
previously observed in XTE J1550-564 (IAUC 7025; Remillard et al.
1999, Ap.J. Let., submitted). Simultaneously with the high-
frequency QPO, QPOs at 5.92 +/- 0.02 Hz [FWHM 2.02 +/- 0.05 Hz; rms
amplitude 2.98 +/- 0.03 percent (2-60 keV; 43.6 sigma)] and at 10.4
+/- 0.1 Hz [FWHM 5.8 +/- 0.3 Hz; rms amplitude 2.55 +/- 0.06
percent (2-60 keV; 23.7 sigma)] are observed. An RXTE observation
taken the day before (on Mar. 3.06), shows a 2-20.0-keV x-ray flux
about 20 percent lower than that of Mar. 4.80 (4.9 x 10E-8 erg sE-1
cmE-2), a softer x-ray spectrum, and a power spectrum with no QPO,
dominated by a weak (2.7 +/- 0.2 percent; 2-60 keV) power-law
component with index -1.23 +/- 0.04. These properties are typical
for those of XTE J1550-564 during the last few months. This
pronounced change in x-ray properties, which took place within 1.8
days, shows that XTE J1550-564 has undergone a major source state
transition. Observations at all wavelengths are encouraged. More
x-ray observations with the RXTE/PCA instrument are required to
study the high-frequency QPO in more detail."
(C) Copyright 1999 CBAT
1999 March 5 (7121) Daniel W. E. Green
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