Central Bureau for Astronomical Telegrams
IAUC 5580: HARD X-RAY TRANSIENT; Cyg X-1
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Circular No. 5580
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
HARD X-RAY TRANSIENT
W. S. Paciesas and M. S. Briggs, University of Alabama, Huntsville;
B. A. Harmon and R. B. Wilson, Marshall Space Flight Center,
NASA; and M. H. Finger, Computer Sciences Corporation, report for
the BATSE team: "We have detected a strong transient hard x-ray
source in data from the BATSE instrument on the Compton Gamma Ray
Observatory. The location is estimated to be at R.A. = 4h.4, Decl.
= +32 (equinox 2000.0), with an error radius of about 1.5 deg. The
source was first detected at an intensity of about 0.2 Crab (20-300
keV) on Aug. 5. By the end of Aug. 8, the flux had reached about 3
Crab and was still increasing. The spectrum is fairly hard (power-
law number index about 2), with significant flux out to at least
300 keV. Although the intensity shows strong variability on short
timescales, no periodicity is evident. Follow-up observations are
encouraged."
CYGNUS X-1
L. Angelini and N. E. White, Laboratory for High Energy
Astrophysics, Goddard Space Flight Center, NASA; and L. Stella,
Osservatorio Astronomico di Brera, Milan, report: "We have independently
discovered 0.04-Hz quasi-periodic oscillations from Cygnus X-1.
This result comes from an ongoing detailed analysis of 13 EXOSAT 1-
to 20-keV Medium Energy (ME) detector x-ray observations made between
1983 and 1986. Power spectra made from the ME timing data are
complex. The typical power spectrum is flat from 0.001 Hz up to a
break frequency that varies between 0.1 and 0.3 Hz from observation
to observation. Above this break frequency, the power spectrum
decreases with a slope of about 1. Superposed on this power law,
there is low-level structure that on occasions appears as a broad
excess, the peak of which varies between 0.7 and 2 Hz from observation
to observation. In a few power spectra, there is also low-
frequency noise below 0.001 Hz caused by absorption dips and long-
term changes in intensity on timescales of hours. A QPO peak is
clearly present at 0.04 Hz, with a FWHM of about 0.07 Hz, in four
of the 13 observations (1983 July 28, 1985 Aug. 12, Oct. 15, and
Oct. 18). This seems to be similar to the 0.04-Hz QPO reported on
IAUC 5576 at energies above 20 Kev. The appearance of this QPO
peak is not correlated with the overall source intensity state, or
orbital phase. However, it is most prominent when the break
frequency is at its lowest value (about 0.1 Hz) with the QPO peak
straddling the break."
1992 August 10 (5580) Daniel W. E. Green
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