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IAUC 6302: 3C 279; 4U 1755-33; NOTICE TO SUBSCRIBERS

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                                                  Circular No. 6302
Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)

3C 279
     F. Makino, H. Inoue, T. Kii, F. Nagase, and A. Yamashita,
Institute of Space and Astronautical Science, on behalf of the ASCA
team, report:  "Following the report of a gamma-ray flare of 3C 279
(IAUC 6294), ASCA observed this region during Jan. 27-28.  From a
quick-look analysis, the 2- to 10-keV flux is estimated to be 1.2 x
10E-11 erg cmE-2 sE-1.  The spectrum is consistent with a power law
with a photon index of about 1.7.  According to the previous ASCA
observations, the 2- to 10-keV flux was (6-9) x 10E-12 erg cmE-2
sE-1 from the middle of 1993 to the beginning of 1995, and was
(1.0-1.6) x 10E-11 erg cmE-2 sE-1 in the middle of 1995.  3C 279
seems to have shown no large intensity change in the band 2-10 keV
since the middle of 1995, in spite of the recent gamma-ray flaring."

4U 1755-33
     M. S. E. Roberts and P. F. Michelson, Stanford University; L.
R. Cominsky, Sonoma State University; and F. E. Marshall, R. H. D.
Corbet, and E. A. Smith, Goddard Space Flight Center, NASA, report:
"On Jan. 30-31, the black-hole candidate 4U 1755-33 was observed by
XTE to be in an off state for the first time.  Preliminary analysis
gives a conservative flux limit of < 1 mCrab, a factor of 100 below
the source's typical intensity.  This offers an unprecedented
opportunity to perform optical spectroscopic measurements of the
companion star.  The optical counterpart normally appears as a
faint (V about 18) blue object associated with reprocessed
radiation from the accretion disk.  Radial-velocity measurements
over the 4.4-hr orbital period could lead to a determination of the
mass function of the compact object.  In addition, a detailed
optical spectrum could determine the spectral type of the companion
and resolve the issue of extreme underabundance of heavy metals in
the accreted material."

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                      (C) Copyright 1996 CBAT
1996 February 2                (6302)            Daniel W. E. Green

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