Central Bureau for Astronomical Telegrams
IAUC 6462: 1996 PW; Cyg X-1
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Circular No. 6462
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)
1996 PW
M. Hammergren, Department of Astronomy, University of
Washington, reports: "Low-resolution reflectance spectra (range
400-1000 nm) of the unusual object 1996 PW were obtained on Aug.
19.42 UT with the Apache Point Observatory 3.5-m telescope (+ DIS).
The spectra display a featureless red-sloped continuum with a
reflectivity gradient S' (Luu 1993, Icarus 104, 138) of 10.2 +/-
0.4 percent (1000 Angstroems)E-1 over the wavelength range 620-860
nm. The object appears significantly redder than the colors
reported on IAUC 6452, which are bluer than solar. No cometary
emission features are seen; however, these spectral characteristics
are consistent with those of cometary nuclei and D-type asteroids
(Luu, op.cit.; Jewitt and Luu 1990, A.J. 100, 933)."
CYGNUS X-1
S. N. Zhang, B. A. Harmon, W. S. Paciesas, C. R. Robinson,
D. M. Scott, and W. Yu, on behalf of the BATSE/CGRO team; and R.
Remillard and W. Cui, on behalf of the ASM/RXTE team, report: "The
blackhole candidate Cyg X-1 is returning to the hard state,
following the recent hard x-ray flux increase (IAUC 6447). Hard x-
ray (20-200 keV) and soft x-ray (1.3-12 keV) fluxes are very close
to the values before the hard-to-soft-state transition in mid-May
1995 (IAUC 6405). Spectral hardening has also been observed in
both bands. The ASM (1.3-12 keV) and BATSE (20-200 keV) long-term
lightcurves are anticorrelated, with the total 1.3- to 200-keV
luminosity remaining approximately unchanged within 15 percent
during the entire state transition from mid-May to late August 1996.
The BATSE and ASM soft-state power-density spectra (PDS) of Cyg X-1
(roughly 10E-7 to 10E-4 Hz), which can be approximately represented
by a power law with an index of approximately -1.0, are apparently
a low-frequency extension of the same soft-state PDS detected by
PCA/RXTE above 10E-3 Hz (Cui et al., submitted to Ap.J. Lett.).
Flaring episodes separated by approximately 45-50 days and of
duration 5-30 days were observed superimposed on the spectral
transition in both ASM and BATSE data. (The mid-1991 to early-1996
BATSE lightcurve for Cyg X-1 does not show evidence of any
significant periodicity near 50 days.) A possible 15-day delay of
the flares in the ASM band with respect to the flares in the BATSE
band was also detected from the cross correlation between ASM and
BATSE lightcurves."
(C) Copyright 1996 CBAT
1996 August 23 (6462) Daniel W. E. Green
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