Central Bureau for Astronomical Telegrams
IAUC 6167: Mkn 421
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Circular No. 6167
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)
Phone 617-495-7244/7440/7444 TWX 710-320-6842 ASTROGRAM CAM
MARSDEN@CFA.HARVARD.EDU or GREEN@CFA.HARVARD.EDU (science)
MARKARIAN 421
T. Takahashi, F. Makino, and T. Kii, Institute of Space and
Astronautical Science; M. Tashiro, H. Kubo, and K. Makishima,
University of Tokyo; T. Ohashi and N. Y. Yamasaki, Tokyo Metropolitan
University; and G. Madejski, Goddard Space Flight Center, NASA,
write: "The BL Lac object Markarian 421 was observed from the x-ray
astronomy satellite ASCA during Apr. 25.8-26.1 UT. The preliminary
energy flux obtained from GIS and SIS abroad ASCA was 1.8 x 10E-10
erg cmE-2 sE-1 (2-10 keV), which is almost the same as that observed
in the previous x-ray/TeV flare in May 1994 (IAUC 5993, 5996). The
photon index was about 2.5. Further x-ray observations were planned
for Apr. 28, 29, May 1, 3, 5, 6, and 8. Observations at optical,
infrared, radio, and other wavelengths are encouraged. For more
details of the x-ray observation schedule, contact T. Takahashi
(e-mail takahasi@astro.isas.ac.jp)."
J. Buckley, J. Quinn, 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, communicate: "Markarian 421 has
been in a period of unusually high activity in TeV gamma-rays. An
intense observing campaign with the Whipple Gamma Ray Telescope was
timed to bracket the EGRET observations that began on Apr. 25.
Analysis of nightly observations gives the following measurements:
Apr. 21, 1.12 +/- 0.13 photons/min; 22, 1.18 +/- 0.11; 23, 0.84 +/-
0.08; 24, < 0.44; 25, 0.42 +/- 0.11; 26, 1.90 +/- 0.12; 27, 1.36
+/- 0.11; 28, 0.81 +/- 0.12; 29, 1.15 +/- 0.10; 30, 1.05 +/- 0.14;
May 1, 0.68 +/- 0.12; 2, < 0.76. Observations generally began at
3h30m UT each day and continued for 3 hr. The statistical
significance of the detections ranged from 3.6 sigma (Apr. 25) to
15.4 sigma (Apr. 26); upper limits are quoted at the 3-sigma level.
The average photon flux between 1995 Jan. 1 and Apr. 5 was also
variable but averaged 0.9 photon/min, corresponding to a flux of
4.3 x 10E-11 photon cmE-2 sE-1. The energy threshold of all
observations was set at 300 GeV in this preliminary analysis.
Observations at other wavelengths are encouraged."
1995 May 4 (6167) Daniel W. E. Green
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