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IAUC 7246: Cas A; N Cir 1999

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                                                  Circular No. 7246
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, 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)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)


CASSIOPEIA A
     H. Tananbaum, Harvard-Smithsonian Center for Astrophysics
(CfA), on behalf of the Chandra X-ray Observatory (representing
scientists at the Chandra X-ray Center, Goddard Space Flight
Center, CfA, Marshall Space Flight Center, Massachusetts Institute
of Technology, Pennsylvania State University, and Space Research
Organization of the Netherlands), reports: "The team has determined
the following position for the pointlike source seen near the
center of Cas A during the Chandra First Light observation:  R.A. =
23h23m27s.94, Decl. = +58o48'42".4 (ICRS, equinox J2000.0).  The
uncertainty in the x-ray position is currently about 2".5 in
radius, but is expected to be reduced to about 1" as the
calibration proceeds.  A quick look at the x-ray data indicates
that any extent is < 2".  The count rate for this source (with a
backside-illuminated ACIS chip) is about 1/3000 of the total x-ray
emission from Cas A over the 0.2-10-keV Chandra band.  An accurate
conversion to flux and luminosity requires the in-flight spectral
response matrices and a careful spectral fitting, but the x-ray
photometry alone suggests that the source luminosity is at least
10**32 erg/s, if it is at the same distance as Cas A.  The source
lies within 5" of the 'expansion center' for the remnant determined
by van den Bergh and Pritchet (1986, Ap.J. 307, 723) after
precessing their position to equinox J2000.0.  There are no obvious
pointlike counterparts within 5" on the Very Large Array 20-cm maps
(http://www.nrao.edu/vla/html/VLA-images.shtml), in the van den
Bergh-Pritchet R-band image (limiting mag about 23.5), or in the
[S II] image of Fesen and Gunderson (1996, Ap.J. 470, 967).  Longer
exposures with Chandra are planned, and these should allow a search
for periodic pulsations.  We suggest that this object might well be
the collapsed star formed at the time of the Cas A supernova
explosion."


NOVA CIRCINI 1999
     Visual magnitude estimates:  Aug. 25.459 UT, 8.1 (A. Pearce,
Nedlands, W. Australia); 25.617, 8.2 (Pearce); 25.996, 8.9 (J. G.
de S. Aguiar, Campinas, Brazil); 26.938, 8.8 (H. C. Vital, Rio de
Janeiro, Brazil); 27.490, 9.2 (Pearce); 28.897, 9.1 (Vital);
29.013, 9.1 (Vital); 30.529, 9.8 (Pearce); 30.901, 9.5 (Vital);
31.533, 9.9 (Pearce); 31.933, 9.0 (Vital); Sept. 1.088, 9.4
(Vital); 1.897, 10.0 (Vital); 2.037, 10.1 (Vital).

                      (C) Copyright 1999 CBAT
1999 September 2               (7246)            Daniel W. E. Green

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