Central Bureau for Astronomical Telegrams
IAUC 6396: Mkn 421; C/1996 B2
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Circular No. 6396
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 421
T. Weekes, Harvard-Smithsonian Center for Astrophysics, reports
for the Whipple Observatory Gamma Ray Collaboration on an
extraordinary outburst of gamma-ray activity from this previously
detected BL-Lac object: "The source was observed on May 7 with the
10-m optical reflector under perfect observing conditions. Using
the standard Whipple observing and analysis technique, we detected
a signal at the 56-sigma level in 2 hr of observation with a
doubling time of 1 hr. The energy threshold for the analysis was
about 350 GeV. Preliminary analysis gives the following counts
(gamma-rays/min): May 7.150-7.170 UT, 5.54 +/- 0.27 (20.8 sigma);
7.180-7.199, 8.29 +/- 0.33 (25.1 sigma); 7.200-7.219, 10.78 +/-
0.36 (30.3 sigma); 7.220-7.240, 12.68 +/- 0.40 (37.7 sigma); 7.240-
7.244, 12.11 +/- 0.91 (13.4 sigma). The average rate of 9.5 gamma-
rays/min is five times larger than for any previous observation
(six times the level of the Crab Nebula) and is the brightest TeV
signal recorded by us from any source to date. Subsequent
observations with the Whipple telescope show that the source has
declined to more usual levels (May 8, 0.62 +/- 0.07 gamma-rays/
minute; May 9, 0.42 +/- 0.09; May 10, 0.79 +/- 0.10). Observations
by P. Garnavich and N. Caldwell with the Whipple 1.2-m optical
telescope indicate a brightening of 0.25 mag in the R band on May
7-10 compared with levels recorded the previous month. Markarian
421 was monitored in x-rays by XTE during May 3-9."
COMET C/1996 B2 (HYAKUTAKE)
C. G. Mason, R. D. Gehrz, T. J. Jones, and D. M. Williams,
University of Minnesota (UM), report infrared photometry of comet
C/1996 B2 using the UM/University of California at San Diego 1.52-m
telescope (+ UM bolometer) at the Mt. Lemmon Observing Facility.
Photometric magnitudes are averaged between Apr. 22.1 and 23.1 UT
using a 13".5 circular aperture with a north-south throw of 129"
between the source and reference beams: J = 4.70 +/- 0.08, H = 4.26
+/- 0.08, K = 3.17 +/- 0.10, L = 0.43 +/- 0.06, M = -0.96 +/- 0.04,
[7.8 microns] = -2.63 +/- 0.03, [8.7 microns] = -3.29 +/- 0.03,
[9.8 microns] = -3.85 +/- 0.03, [10.3 microns] = -4.11 +/- 0.04,
[11.6 microns] = -4.14 +/- 0.05, [12.5 microns] = -3.69 +/- 0.05,
and [18.0 microns] = -4.29 +/- 0.04. The infrared spectral energy
distribution shows a dust temperature about 40 percent higher than
would be expected for small black spheres at the same heliocentric
distance. The 10- and 20-micron silicate emission features are
quite strong.
(C) Copyright 1996 CBAT
1996 May 11 (6396) Daniel W. E. Green
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