Central Bureau for Astronomical Telegrams
IAUC 6324: GRO J1744-28; 22P
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Circular No. 6324
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)
GRO J1744-28
M. J. Stark, University of Maryland and the Laboratory for
High Energy Astrophysics, Goddard Space Flight Center (LHEA/GSFC);
A. Baykal, National Research Council and LHEA/GSFC; T. Strohmayer,
Universities Space Research Association and LHEA/GSFC; and J. H.
Swank, LHEA/GSFC, communicate: "We have detected, with the
Proportional Counter Array (PCA) onboard the X-ray Timing Explorer
(XTE), glitches in the arrival times of x-ray pulses from GRO
J1744-28 that occur during the x-ray/gamma-ray bursts seen from
this source. Timing of the pulses before and after the burst
events shows a clear advance in the pulse arrival times of about 25
ms (5 percent of the 0.467-s period). The advance occurs within a
time interval no longer than 25 or 30 s, after which the advance
decays. The functional form of this decay is not yet precisely
known, but the best-fit of an exponential function to it has a time
constant of about 500 s. This behavior is exhibited during all
bursts so far observed from this source by XTE, and these pulse
timing considerations have been used to identify additional bursts
that occurred when the PCA was not operating. The flux from GRO
J1744-28 is depressed slightly following a burst but recovers to
its pre-burst level within a few hundred seconds, while the phase
shift recovers in about 1500 s. The pulse shapes before and after
the bursts are very similar. Interpreted in terms of a fractional
change in the angular velocity, the short time during which the
advance occurs indicates such a change of at least 10E-3, whereas
the largest such change seen in radio-pulsar glitches is 10E-6. If
10E20 g of material with the angular momentum that is
characteristic of the co-rotation radius (10**8 cm) are accreted,
the fraction of the star's moment of inertia participating in the
glitch is about 10E-6, equivalent to the moment of inertia of a
thin shell containing 10E-6 of the neutron-star mass. This is much
less than the fraction of the moment of inertia thought to
participate in radio-pulsar glitches."
COMET 22P/KOPFF
Total magnitude estimates: Feb. 18.19 UT, 13.0 (H. Mikuz,
Ljubljana, Slovenia, 0.20-m reflector + CCD + V filter); 19.51,
12.4 (A. Hale, Cloudcroft, NM, 0.41-m reflector, visual); 23.46,
12.2 (Hale).
(C) Copyright 1996 CBAT
1996 February 23 (6324) Daniel W. E. Green
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