Central Bureau for Astronomical Telegrams
IAUC 6927: XTE J1855-026; XTE J2012+381; 1998bn
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Circular No. 6927
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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XTE J1855-026
R. Corbet, Goddard Space Flight Center (GSFC) and Universities
Space Research Association, reports on behalf of the RXTE ASM team
at GSFC and the Massachusetts Institute of Technology: "An analysis
of the RXTE All Sky Monitor light curve of the 362-s pulsar XTE
J1855-026 (IAUC 6904) obtained between 1996 Jan. 6 and 1998 May 28
reveals a modulation at a period of about 6.1 days. A sine-wave
fit yields 6.074 +/- 0.004 days, with an amplitude of 0.15 counts/s
and time of maximum flux of JD 2450289.6 +/- 0.2. The mean count
rate during this period was 0.5 counts/s, which corresponds to
about 7 mCrab (2-12 keV). This combination of pulse and orbital
parameters raises the possibility that this may be a supergiant,
rather than a Be star system, as earlier suggested. If this is a
Be star system, then a 6-day orbital period would be the shortest
known for this class."
XTE J2012+381
N. E. White, Goddard Space Flight Center; and Y. Ueda, T.
Dotani, and F. Nagase, Institute of Space and Aeronautical Science,
report: "This x-ray transient (IAUC 6920) was observed with the
ASCA x-ray observatory from May 29.30 to 30.19 UT. The source
position was determined to be R.A. = 20h12m39s.1, Decl. =
+38o10'50" (equinox 2000.0), with an uncertainty of 0'.5. This
position contains that of the variable radio source (IAUC 6924).
The ASCA position also overlaps the 1' RXTE PCA error circle (IAUC
6922). The x-ray intensity in the band 0.7-4 keV increased
linearly by 15 percent across the observation, whereas the 4-10-keV
flux remained constant. The average 2-10-keV-band flux was 150
mCrab. Applying a disk blackbody and power-law model to the ASCA
GIS spectrum in the range 1-10 keV yields an acceptable fit with a
temperature of the innermost disk of 0.76 +/- 0.01 keV, a power-law
photon index of 2.9 +/- 0.1, and an absorption column density (1.29
+/- 0.03) x 10E22 cmE-2. This ultrasoft spectrum with a hard
power-law tail is the well established x-ray signature of blackhole
candidates. If the x-ray absorption is due to the interstellar
medium, it corresponds to 7 magnitudes of extinction in the V band."
SUPERNOVA 1998bn IN NGC 4462
Visual magnitude estimates: May 5.76 UT, 13.5 (B. Monard,
Pretoria, S. Africa); 14.70, 14.0 (Monard); 23.8, 15.5 (L. Kiss,
Agasvar, Hungary).
(C) Copyright 1998 CBAT
1998 June 2 (6927) Daniel W. E. Green
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