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IAUC 6178: Mkn 501; BL Lac; 71P

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                                                  Circular No. 6178
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)


MARKARIAN 501
     The Whipple Observatory Gamma Ray Collaboration (J. Quinn, J.
Buckley, and T. C. Weekes, Smithsonian Astrophysical Observatory;
M. Catanese, D. A. Carter-Lewis, F. Krennrich, R. C. Lamb, and J.
Zweerink, Iowa State University; C. W. Akerlof, D. Meyer, and M.
Schubnell, University of Michigan; J. Gaidos, G. Sembroski, and C.
Wilson, Purdue University; D. J. Fegan, R. Lessard, and J. McEnery,
University College, Dublin; M. F. Cawley, St. Patrick's College,
Maynooth; and S. Biller, A. M. Hillas, A. Rodgers, and J. Rose,
University of Leeds) communicates:  "TeV gamma-rays have been
detected from the BL Lac-object Markarian 501 with the high-
resolution imaging camera on the Whipple 10-m optical reflector
between Mar. 28 and June 5.  A flux was detected in 57 hr of
observation at the 10-sigma level.  The flux above 0.3 TeV was
about 8 x 10E-12 photon cmE-1 sE-1 (or 0.07 that of the Crab
Nebula).  The TeV-gamma-ray source's location is within 10' of the
known position of Mrk 501 (R.A. = 16h52m.2, Decl. = +39o50',
equinox 1950.0) and consistent with this identification.  Mrk 501,
at a redshift of 0.034, is similar in some respects to the
previously detected TeV-BL Lac source Mrk 421 (Kerrick et al. 1995,
Ap.J. 438, L59, and references therein); however, it does not yet
show the same evidence for TeV variability as Mrk 421, nor has it
yet been detected at MeV to GeV gamma-ray energies."


BL LACERTAE
     R. D. Jeffries and M. R. Thurston, University of Birmingham;
and D. J. Axon, Space Telescope Science Institute, communicate: "We
have observed BL Lac in photometric conditions with the 1-m Jacobus
Kapetyn telescope (+ CCD camera) at La Palma.  A comparison with a
photometric sequence in the CCD field yields:  June 4.21 UT, V =
15.76 +/- 0.02, B-V = +1.03 +/- 0.02; 6.18, 15.61 +/- 0.02, 0.97
+/- 0.03; 7.20, 15.51 +/- 0.02, 0.97 +/- 0.02, U-B= -0.16 +/- 0.03.
This confirms the suspicion of Vermeuelen et al. (IAUC 6176) that
BL Lac is currently in a very low state at around its historical
minimum."


COMET 71P/CLARK
     Visual magnitude estimates by A. Hale, Cloudcroft, NM (0.41-m
reflector):  May 28.44 UT, 11.3; June 3.40, 11.2.


1995 June 16                   (6178)            Daniel W. E. Green

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