Central Bureau for Astronomical Telegrams
IAUC 6709: C/1996 J1; Mkn 421 AND Mkn 501
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Circular No. 6709
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/cfa/ps/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)
COMET C/1996 J1 (EVANS-DRINKWATER)
Z. Sekanina, Jet Propulsion Laboratory and European Southern
Observatory, writes: "A refined orbital solution (cf. IAUC 6662),
based on my standard model for split comets (1982, in Comets, 251)
and derived from 20 accurate separations of the secondary nucleus A
from the primary B between 1997 May 9 and June 16 (MPC 29700 and
29967), suggests that the comet broke up on 1996 Oct. 11.1 +/- 1.6
UT (or 80 days before perihelion) with a velocity of 0.93 +/- 0.03
m/s in a direction nearly normal to the orbit plane, and that A
drifted away from B with a relative nongravitational deceleration
of 39.3 +/- 0.3 units of 10E-5 the solar attraction. Predicted
separation distances and position angles for companion A relative
to primary B (for 0h UT on each date): 1997 July 31, 130", 268 deg;
Aug. 20, 146", 269 deg; Sept. 9, 162", 269 deg; Sept. 29, 177",
267 deg; Oct. 19, 187", 265 deg; Nov. 8, 187", 262 deg; Nov. 28,
180", 260 deg; Dec. 18, 168", 260 deg."
Total visual magnitude estimate by K. Hornoch, Lelekovice,
Czech Republic (0.35-m reflector): July 13.98 UT, 13.6.
MARKARIAN 421 AND MARKARIAN 501
C. L. Bhat, Bhabha Atomic Research Centre (BARC), Mumbai,
writes: "The Imaging Element of the TeV gamma-ray telescope array
TACTIC (Bhat et al. 1994, Proc. 'Towards a Major Atmospheric
Cerenkov Detector III', Univ. Acad., Tokyo) recently set up by BARC
group at Mt. Abu, India, has been used to observe Mkn 501 and Mkn
421 in the tracking mode for about 50 and 29 hr, respectively. The
data have been analyzed using the 'supercuts' techniques (Reynolds
et al. 1993, Ap.J. 404, 206). A 13.3-sigma confidence level gamma-
ray signal has been detected from Mkn 501 during April-May, with a
time-averaged flux of (7.6 +/- 0.7) x 10E-11 photons cmE-2 sE-1
above 0.7 TeV (about twice the Crab flux). A peak flux of nearly
four times that of the Crab has been recorded recently by the
TACTIC on Apr. 13 (in agreement with the results reported by the
Whipple, CAT, and HEGRA groups) and again on May 16. Significant
flux variability has been observed on a day-to-day basis with
pronounced dips on Apr. 12, May 14, and May 30. In the case of Mkn
421, our observations reveal that this source was in a
comparatively low state of activity during Apr. 7-13 and May 7-29.
A 3-sigma upper limit of 1.7 x 10E-11 photons cmE-2 sE-1 above 0.8
TeV is deduced for the corresponding time-averaged flux."
(C) Copyright 1997 CBAT
1997 July 29 (6709) Daniel W. E. Green
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