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IAUC 6415: Cyg X-1; GRO J1744-28; C/1996 B2

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                                                  Circular No. 6415
Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)

     T. Dotani, H. Negoro, K. Mitsuda, H. Inoue, and F. Nagase,
Institute of Space and Astronautical Science, communicate on behalf
of the ASCA team:  "We observed Cyg X-1 with ASCA during May 30.23-
31.14 UT with a net exposure time of about 33 000 s.  Cyg X-1 was
in a high, soft state during the observations.  The GIS intensity
in the range 1-10 keV was about 1000 counts/s (after deadtime
correction), which corresponds to about 1.3 Crab.  The observed
flux in 1-10 keV was 3.2 x 10E-8 erg sE-1 cmE-2.  The energy
spectrum can be approximated by a blackbody with a hard tail.  The
best-fitting temperature of the blackbody is 0.34 +/- 0.02 keV, and
the hard tail can be approximated by a power law with a photon
index of 2.4 +/- 0.1.  The blackbody and the power-law components
cross over around 2.3 keV, above which the power-law component
becomes dominant."

GRO J1744-28
     J. M. Kommers, R. E. Rutledge, D. W. Fox, W. H. G. Lewin, and
E. H. Morgan, Massachusetts Institute of Technology; C. Kouveliotou,
Universities Space Research Association; and J. van Paradijs,
University of Alabama in Huntsville and University of Amsterdam,
report:  "We found strong quasiperiodic oscillations (QPOs) with a
frequency of about 0.4 Hz in a burst from GRO J1744-28 observed on
about June 4.617 UT with the PCA instrument onboard the Rossi X-ray
Timing Explorer.  The burst was the sixth of seven seen on June 4.
The oscillations are clearly visible in the lightcurve during the
last 25 s of the 40-s burst.  A power spectrum of these 25 s shows
a peak near 0.4 Hz, with FWHM < 0.08 Hz (the upper limit being set
by our frequency resolution) and a fractional rms amplitude of the
mean burst flux during these 25 s (in excess of the quiescent flux)
of 25 +/- 5 percent (not corrected for deadtime).  We have also
identified QPOs with frequencies in the range 0.3-0.5 Hz in the
emission following at least 10 of 82 bursts observed between late
January and late April.  These QPOs typically lasted for about 30 s,
although in one burst they lasted as long as 80 s; the fractional
rms amplitudes exceeded 15 percent in some cases."

     Naked-eye m1 estimates by D. Seargent, The Entrance, N.S.W.:
May 17.81 UT, 3.9; 21.80, 4.1; 23.81, 4.3; 26.79, 4.4; 28.79, 4.5;
30.79, 4.8.

                      (C) Copyright 1996 CBAT
1996 June 6                    (6415)            Daniel W. E. Green

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