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IAUC 7345: Mkn 421; 1999gs; C/1995 O1

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                                                  Circular No. 7345
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)

     C. Gouiffes, Centre d'Etudes de Saclay, Gif-sur-Yvette,
forwards the following message for B. Degrange, who writes on
behalf of the CAT collaboration (Centre d'Etude Spatiale des
Rayonnements, Toulouse; College de France, Paris; Laboratoire de
Physique Nucleaire et des Hautes Energies (LPNHE) Ecole
Polytechnique; LPNHE, Universites Paris VI et VII; Service
d'Astrophysique, Centre d'Etudes de Saclay; University of
Perpignan; Charles University, Prague; and Olomouc University):
"High-TeV activity has been observed recently from the BL Lac
object Mkn 421, using the very-high-energy gamma-ray CAT telescope
located in the French Pyrenees and operating at an energy
threshold of 250 GeV.  Mkn 421 was observed on Jan. 7, 11, 12, and
13 with a total on-source exposure time of 12.5 hr.  A preliminary
analysis indicates that the source was variable on a daily
timescale with the following average nightly flux levels, in units
of the Crab Nebula flux:  Jan. 7.13 UT, 0.45; 11.15, 2.3; 12.1,
1.9; 13.1, 1.3."

SUPERNOVA 1999gs IN NGC 4725
     W. D. Li, University of California at Berkeley, on behalf of
the Lick Observatory Supernova Search (cf. IAUC 6627, 7126), report
the discovery with the 0.8-m Katzman Automatic Imaging Telescope
(KAIT) of an apparent supernova in NGC 4725.  The new object was
discovered at mag about 19.3 on an unfiltered image (limiting mag
about 19.5) taken on 1999 Dec. 28.5 UT, and it was confirmed on a
5-min unfiltered image (limiting mag about 21.0) taken on Dec.
30.5.  SN 1999gs is located in the southern spiral arm of the
galaxy at R.A. = 12h50m26s.28, Decl. = +25o28'16".5 (equinox
2000.0), which is 3" west and 105" south of the nucleus of NGC
4725.  Another observation obtained on 2000 Jan. 13.5 showed the
new object still at mag about 19.5 (limiting mag 20.5).  A template
image of NGC 4725, made by combining several observations of the
field before 1999 June 7, showed nothing at the position of SN
1999gs (limiting mag about 20.5).  The discovery images can be
found at http://astron.berkeley.edu/~bait/1999/ngc4725.html.  LOSS
has not observed this galaxy for about half a year, so SN 1999gs
must be a very old supernova.

     Visual m_1 estimates by A. Pearce, Nedlands, W. Australia
(0.41-m reflector):  1999 Nov. 1.80 UT, 12.9; Dec. 14.81, 12.9;
2000 Jan. 8.70, 13.3.

                      (C) Copyright 2000 CBAT
2000 January 14                (7345)            Daniel W. E. Green

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