Central Bureau for Astronomical Telegrams
IAUC 6338: GRO J1744-28; alpha Cen C
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Circular No. 6338
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
B. Giles and T. Strohmayer, Goddard Space Flight Center and
Universities Space Research Association, report: "The PCA
experiment onboard XTE has now observed the galactic-center
transient GRO J1744-28 (IAUC 6291) fourteen times for 1698 min
during the period Jan. 18-Mar. 5. The nonbursting flux below 15
keV shows a linear decline since late January, which if continued
will reach zero about 1 week into April. This is a slower decrease
than reported by BATSE for 20-100 keV (IAUC 6335). The flux in the
main bursts is also decreasing, but at a slower rate, and will if
continued reach zero about 40-50 days later. A total of 50 large
bursts has been seen (6- to 8-fold increase over the persistent
emission, 10-15 min exponential recovery). In addition, at least 5
'mini-bursts' have occurred, where the flux increases by a factor
of 2 and the recovery takes 20 s or less. The mini-burst duration
appears slightly less than the more frequent, larger bursts. Many
even smaller and shorter burst events often seem to be clustered in
the few minutes prior to a large burst and are good predictors of
the main events; these 'micro-bursts' last 1-2 s and show a 20- to
50-percent increase in countrate over the mean persistent rate.
Finally, there are occasions when the flux appears to be primarily
comprised of numerous spiky bursts of duration about 1 s. This
spiky variability is substantial compared to the statistical error
over the 0.1- to 2-s timescale and to the about 10-percent
modulation at 2.2 Hz. The appearance of the similar bursting
behavior (burst followed by a recovery in the flux) over such a
wide range of amplitudes argues that a single phenomenon, such as
accretion of plasma blobs of varying mass, may account for
essentially all the source emission."
alpha CENTAURI C
E. Guinan and N. Morgan, Villanova University, report the
determination of the rotation period of Proxima Cen (alpha Cen C)
from the analysis of 3.5 months of monitoring with the
International Ultraviolet Explorer during 1995 May-August:
"Periodic variations in the strength of the Mg II h+k 280-nm line
emission were found having a period of 31.5 +/- 1.5 days and a mean
amplitude of 20-25 percent. The observed modulation in the
chromospheric Mg II emission arises as large active regions
covering the dM4 star's surface rotate in and out of view. Several
flares were also observed. This rotation period is slightly faster
than the 36.8 days found for alpha Cen B using the same method (see
IAUC 6259)."
(C) Copyright 1996 CBAT
1996 March 8 (6338) Daniel W. E. Green
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