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IAUC 6963: 1E 1740.7-2942; N Sgr 1998; C/1998 J1

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                                                 Circular No. 6963
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
Phone 617-495-7244/7440/7444 (for emergency use only)


1E 1740.7-2942
     D. M. Smith, Space Sciences Laboratory, University of
California at Berkeley (UCB/SSL); S.-N. Zhang, Universities Space
Research Association and Marshall Space Flight Center (MSFC), NASA;
D. Main, UCB/SSL; and B. A. Harmon, MSFC, report:  "This black-hole
candidate and microquasar is entering a hard-x-ray low-flux state
for the first time in three years.  The decline was measured by
CGRO/BATSE beginning between Mar. 18 and Apr. 7, from between 100
and 150 mCrab (20-100 keV) to about 30-50 percent of that level at
present.  In the RXTE PCA (2.5-25 keV), a spectral softening began
around Mar. 21 from power-law index 1.5 to 1.7, but the count rate
only declined after Apr. 20 and is now at 60 percent of maximum.
Comparison with similar declines in 1990-1991 and 1994 (BATSE and
SIGMA data) indicates a possible period of 1300-1400 days.  If the
pattern repeats, the low state should last several months.
Observations are strongly encouraged at all wavelengths not
excessively absorbed near the Galactic center."


NOVA SAGITTARII 1998
     Y. Lipkin, A. Retter, and E. M. Leibowitz, Wise Observatory,
Tel Aviv University, report:  "On June 7, 8, 9, 11, 12, and 13, we
performed CCD photometry of N Sgr 98 with the 1-m Wise telescope
through an I filter for about 5 hr each night.  The light curve is
modulated coherently for at least 40 cycles, with either one of
the two periodicities (0.17330 or 0.14765 +/- 0.00011 day), which
are 1-day aliases of each other.  The folded data resemble an
eclipse light curve, with an average dip of 0.014 mag.  It is
likely that similar periodicity modulates the light curve of the
star as measured by us already on May 11 and 12."
     Visual magnitude estimates by K. Hornoch, Lelekovice, Czech
Republic:  June 20.96 UT, 11.3; 21.96, 11.3; 26.00, 11.4; 28.96,
11.3.


COMET C/1998 J1 (SOHO)
     Visual m_1 estimates:  June 8.90 UT, 6.1 (H. C. Vital, Rio de
Janeiro, Brazil, 12x50 binoculars); 12.94, 6.8 (W. C. de Souza, Sao
Paulo, Brazil, 11x80 binoculars); 18.32, 7.0 (S. T. Rae, Palmerston
North, N.Z., 10x50 binoculars); 23.91, 7.6 (de Souza); 28.28, 7.6
(Rae, Te Awamutu, N.Z.).

                      (C) Copyright 1998 CBAT
1998 July 2                    (6963)            Daniel W. E. Green

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