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IAUC 6300: 1996 B2; GRO J1744-28

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                                                  Circular No. 6300
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)


COMET 1996 B2
     Additional precise CCD observations:

     1996 UT             R.A. (2000) Decl.       Observer
     Feb.  1.11706   14 32 21.41   -24 56 09.2   Tichy
           1.12694   14 32 21.90   -24 56 08.9     "
           1.12980   14 32 22.05   -24 56 09.2     "
           1.21501   14 32 26.06   -24 56 11.5   Sarounova
           1.21716   14 32 26.14   -24 56 11.2     "
           1.22469   14 32 26.47   -24 56 11.4     "

M. Tichy (Klet).  0.57-m f/5.2 reflector.
L. Sarounova, P. Pravec, and M. Wolf (Ondrejov).  0.65-m reflector.


GRO J1744-28
     W. Zhang, Goddard Space Flight Center (GSFC) and Universities
Space Research Association; E. Morgan, Massachusetts Institute of
Technology; J. Swank and K. Jahoda, GSFC; and G. Jernigan and R.
Klein, University of California at Berkeley, report:  "GRO J1744-28
showed quasi-periodic intensity oscillations (QPO) in the energy
band 3-12 keV during an 11-hr XTE observation starting on Jan.
18.77 UT.  The power spectrum in the frequency band 5-100 Hz
consists of a red-noise component that can be characterized by a
power law with an index of -1 and three QPO peaks centered,
respectively, at 20, 40, and 60 Hz.  The peaks at 20 and 60 Hz are
clearly discernible, yet hard to quantify at this stage of the
analysis.  The peak at 40 Hz can be well characterized by a
Lorentzian profile with a FWHM of 27 Hz.  The total integrated
power under the 40-Hz peak amounts to a fractional RMS variation of
5.6 percent (not corrected for the effect of detector deadtime).
The effect of flares on the centroid frequencies and the strength
of the oscillations is currently under study.  It is not clear
whether the standard beat frequency model can accommodate this QPO
because of the high frequencies.  The pulsation at 2 Hz (IAUC 6285)
and the energy spectrum (IAUC 6291) imply a strong magnetic field,
which probably prevents the accretion disk from extending so close
to the neutron star as to have keplerian frequencies as high as the
observed QPO frequencies, even if one takes into account the
presumably very high luminosity."

                      (C) Copyright 1996 CBAT
1996 February 1                (6300)            Daniel W. E. Green

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