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IAUC 6710: XTE J1755-324; 1987A

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                                                 Circular No. 6710
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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XTE J1755-324
     R. Remillard and A. Levine, Massachusetts Institute of
Technology (MIT); and J. Swank and T. Strohmayer, Goddard Space
Flight Center (GSFC), report for the RXTE ASM Team at MIT and GSFC:
"The All Sky Monitor of the Rossi X-ray Timing Explorer detected a
new x-ray source late on July 25 UT, whose position was determined
with the PCA early on July 29 to be R.A. = 17h55m28s.6, Decl. =
-32o28'39" (equinox 2000.0; uncertainty 1').  By July 28, the flux
had increased to 170 mCrab (2-12 keV).  The x-ray spectrum is
substantially steeper than that of the Crab nebula.  The spectrum
appears complex, roughly consistent with a 0.7-keV disk blackbody
combined with a hard component that extends above 10 keV.  The flux
is 2.9 x 10E-9 erg cmE-2 sE-1 at 2-20 keV.  The interstellar column
density appears to be substanitally less than 1.0 x 10E22 atoms
cmE-2.  Optical and radio observations are strongly encouraged."

     P. Garnavich, R. Kirshner, and P. Challis, Harvard-Smithsonian
Center for Astrophysics, report on behalf of the Supernova
Intensive Study team that images of SN 1987A and its circumstellar
emission rings were obtained with the Hubble Space Telescope (HST)
Wide Field and Planetary Camera 2 (WFPC2) on July 10.  A comparison
between the narrow-band H-alpha (F656N) image and a WFPC2 image
taken with the same filter in 1994 Feb. shows that a compact region
near the inner ring has significantly increased in brightness (50
+/- 5 percent), while the rest of the ring emission continues to
fade slowly.  The region is located 0".55 +/- 0".02 from the
supernova at p.a. 29 +/- 2 deg and appears unresolved.  This
position is projected slightly within the ring, being 87 +/- 4
percent of the separation between the supernova and the peak of the
ring emission.  The position of the bright spot is coincident with
the blue-shifted-emission feature detected with STIS (IAUC 6665).
Broad-band F675W (R) WFPC2 images show that the region remained at
a nearly constant brightness between 1994 Oct. and 1996 Feb., while
in the past 16 months the feature has brightened by 33 +/- 5
percent (to R = 21.7).  A similar increase in brightness is seen in
the F336W (U), F439W (B), F555W (V), and F814W (I) filters, as well
as the F502N filter (which isolates the [O III] 500.7-nm emission
line).  The sudden flux increase, combined with the spectral
character and position of the spot within the ring, suggests that
this is the first optical evidence of the collision between the
supernova ejecta and the slow-moving progenitor wind."

                      (C) Copyright 1997 CBAT
1997 July 30                   (6710)            Daniel W. E. Green

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