Central Bureau for Astronomical Telegrams
IAUC 6439: Cyg X-1; 1983ab
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Circular No. 6439
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)
CYGNUS X-1
W. Cui, Center for Space Research, Massachusetts Institute of
Technology; W. Focke, University of Maryland and Goddard Space
Flight Center (GSFC); and J. Swank, GSFC, report: "The ASM
lightcurve indicates that Cyg X-1 is still in the high state, and
its 1.3-12-keV flux has been varying between about 0.8 and 1.5 Crab
since the transition (IAUC 6404). So far, twelve snapshots (public)
of the source have been made with RXTE. In the PCA band (2-60 keV),
the x-ray flux varied between about 0.4 and 1 Crab. After an
apparent 'settling period' (covered by the first three observations),
both the energy spectrum and power-density spectrum (PDS) seem to
be stabilized. The energy spectrum can be described by a model
consisting of a soft-blackbody component (kT about 0.3 keV) and a
broken power law whose photon index breaks from about 2.9 to 2.0 at
about 11 keV. The PDS can be characterized by a power law, with a
slope of about -1 (i.e., 1/f), below about 16 Hz and a steeper one
above, with a slope of about -2. The observation made on June
17.332-17.380 UT shows the presence of quasiperiodic oscillations
(QPOs) centered at about 52 mHz (Lorentzian width about 19 mHz),
only when the source reaches a flux peak at about 1 Crab. The
integrated fractional rms of the QPO is about 8, 11, and 10 percent
in the energy bands 2-6.5, 6.5-13.1, and 13.1-60 keV, respectively.
It is not clear if this QPO is related to the 40-mHz QPO reported
for the low state (IAUC 5576, 5580)."
SUPERNOVA 1983ab IN ANONYMOUS GALAXY
N. Samus and S. V. Antipin, Sternberg Astronomical Institute,
report the discovery by Antipin of a supernova on Moscow collection
plates taken with the Crimean 0.40-m astrograph. The coordinates
of the supernova measured on the discovery plates relative to GSC
stars are R.A. = 16h22m34s.0, Decl. = +36o45'25" (equinox 2000.0),
which is 6" west and 5" north of the galaxy's center. SN 1983ab is
seen on 24 plates, the first being a plate exposed on 1983 Aug.
27.76 UT (at mag B = 17.07) and the last taken on Sept. 14.85 (at B
= 16.86:); maximum brightness (B = 16.35 +/- 0.15) occurred on Sept.
4. SN 1983ab is not present (B [17.7) on a plate taken on 1983 Aug.
16.87, nor is it visible on one taken on 1983 Sept. 27.72 (B [17.7).
SN 1983T was discovered by N. Metlova on the same plates (cf. IAUC
3873).
(C) Copyright 1996 CBAT
1996 July 25 (6439) Daniel W. E. Green
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