Central Bureau for Astronomical Telegrams
IAUC 6337: GRO J1744-28; C/1995 Y1
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Circular No. 6337
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
T. Dotani, Y. Ueda, M. Ishida, F. Nagase, and H. Inoue,
Institute of Space and Astronautical Science; and Y. Saitoh,
University of Tokyo, communicate on behalf of the ASCA team: "We
observed GRO J1744-28 with ASCA between Feb. 26.42 and 27.09 UT
with a net exposure time of about 20 000 s. We detected a bright
bursting/pulsating source at a location consistent with the VLA
position (IAUC 6323). The GIS intensity of the persistent
component in the range 1-10 keV was about 130 counts/s (after
deadtime correction). The energy spectrum of the persistent
emission is hard, is contaminated by a large soft x-ray absorption,
and can be approximated by a power law with photon index alpha =
1.22 and absorbing column density NH = 5.1 x 10E22 cmE-2. In
addition, a structure is seen that appears as a broad hump around 6
keV and an edge at 7 keV and that can be attributed to a highly
absorbed component. Assuming a cosmic abundance of iron, one
requires a column density of 2 x 10E23 cmE-2 to explain the 7-keV
edge structure. With the inclusion of this highly-absorbed
component, the photon index of the power-law component becomes a
little steeper, alpha about 1.36 +/- 0.02, with NH = (5.3 +/- 0.1)
x 10E22 cmE-2. The average flux of the persistent component was
1.9 x 10E-8 erg sE-1 cmE-2 in the range 2-10 keV, which corresponds
to about 900 mCrab. The apparent barycentric pulse period was
found to be 0.467033(5) s on Feb. 26.76 UT. The pulse profile is
almost sinusoidal with a single peak, and the pulse fraction in the
band 2-10 keV is about 10 percent (peak-to-peak). After correction
for the orbital doppler effect using the parameters on IAUC 6286, the
intrinsic pulse period at this epoch is estimated to be 0.467039 s.
A total of nine bursts was detected during about 16 000 s of high-
time-resolution data. The duration of bursts is about 10 s, and
their peak flux is an order of magnitude larger than the persistent
flux. After the decay of the bursts, the persistent flux decreased
by 30 percent and then returned to the preburst level within a few
hundred seconds. The energy spectrum of bursts is similar to, but
slightly harder than, the persistent emission. The burst spectrum
can be well fitted by a power law with alpha = 1.01 +/- 0.04 and NH
= (6.1 +/- 0.2) x 10E22 cmE-2."
COMET C/1995 Y1 (HYAKUTAKE)
Visual m1 estimates: Feb. 18.25 UT, 8.0 (A. Pereira, Cabo da
Roca, Portugal, 9x34 binoculars); 28.23, 8.1 (J. Shanklin, Minera,
Wales, 14x100 binoculars); Mar. 2.77, 8.7 (A. Pearce, Lockington,
Victoria, 20x80 binoc.).
(C) Copyright 1996 CBAT
1996 March 7 (6337) Daniel W. E. Green
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