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IAUC 7595: 2001ab; V4643 Sgr; GRS 1758-258

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                                                  Circular No. 7595
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)
CBAT@CFA.HARVARD.EDU (science)
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SUPERNOVA 2001ab IN NGC 6130
     A. B. Aazami and W. D. Li, University of California at
Berkeley, on behalf of LOTOSS (cf. IAUC 7514), report
the discovery of an apparent supernova on unfiltered CCD images
taken on Mar. 11.5 (mag about 17.5) and 12.5 UT (mag about
17.4) with the 0.8-m Katzman Automatic Imaging Telescope (KAIT).
SN 2001ab is located at R.A. = 16h19m34s.83, Decl. =
+57 37'05".5 (equinox 2000.0), which is 10".9 east and 11".4
north of the nucleus of NGC 6130.  A KAIT image taken on 2000
Aug. 15.3 showed nothing at this position (limiting mag about
19.0).


V4643 SAGITTARII
     A. Nakamura, Kuma, Ehime, Japan, reports the following
magnitudes for V4643 Sgr by A. Tago (Tsuyama, Okayama),
which he derived (using GSC comparison stars) from his T-Max
400 film exposures obtained with a 105-mm f/4 camera lens:
Feb. 19.863 UT, [10.0; 22.860, [9.8; 26.870, 9.5


GRS 1758-258
     D. M. Smith, Space Sciences Laboratory, University of
California at Berkeley; C. Markwardt, Goddard Space Flight
Center (GSFC); W. A. Heindl, Center for Astrophysics and Space
Science, University of California at San Diego; and J. H. Swank,
GSFC, using data from the RXTE PCA, report:  "The black-hole
candidate and microquasar GRS 1758-258 has entered an extremely
dim state.  The power law (usually photon index -2), which
normally dominates the spectrum, has dropped by an order of
magnitude in luminosity (from 10**-9 to 10**-10 erg
cm**-2 s**-1, 2-20 keV) and softened to index -3,
leaving the spectrum dominated by the faint thermal component
that is often present (kT = 0.4 keV).  The change occurred
abruptly:  the power law was as bright as usual on Feb. 21,
and on Feb. 27, Mar. 2, and 6 was in the dim state, with
little apparent change among the latter three observations.
We identify this with the 'off' state last reported by SIGMA
in 1991-1992 (Gilfanov et al. 1993, Ap. J. 418, 844).  The
remaining soft emission may be the extended emission reported
by Chandra from this source (Heindl and Smith 2000, Bull. A.A.S.
32, 1603).  Observations are strongly encouraged at all
wavelengths not excessively absorbed near the Galactic center,
both to characterize this x-ray state and to search for changes
in the optical candidates for this source's companion, now that
the accretion disk may have turned off."

                      (C) Copyright 2001 CBAT
2001 March 12                  (7595)            Daniel W. E. Green

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