Central Bureau for Astronomical Telegrams
IAUC 6888: 1998bn; Mkn 421
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Circular No. 6888
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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SUPERNOVA 1998bn IN NGC 4462
F. Patat, European Southern Observatory (ESO); and M. Maia,
Observatorio Nacional, Rio de Janeiro, write: "We observed SN
1998bn with the ESO 1.5-m telescope (+ Boller & Chivens
spectrograph; 5-min exposure, range 360-750 nm, resolution 0.5 nm)
on Apr. 28.10 UT. A full reduction of the CCD spectrogram shows
that this is a type-Ia supernova, about 4 days before maximum
light, very similar to the well-studied SN 1994D (Patat et al.
1996, MNRAS 278, 111). The spectrum is dominated by a multitude of
lines with the usual P-Cyg profiles, superimposed on a blue
continuum. Most of the lines arise from Si II, S II, Fe II, and Fe
III. The expansion velocities deduced from the minima of Si II
635.5-nm and Ca II H and K are 11 500 and 15 500 km/s, respectively.
An unresolved interstellar absorption of Na I D, arising in the
parent galaxy, is clearly visible at 592.4 nm, with an equivalent
width of 0.08 nm. The recession velocity deduced from this feature
(1580 km/s) is slightly smaller than the value reported by Tully
(1988, Nearby Galaxies Catalog) for NGC 4462 (1866 km/s)."
MARKARIAN 421
T. Takahashi, K. Maegami, F. Makino, and H. Ozawa, Institute
of Space and Astronautical Science; and H. Kubo, Institute of
Physical and Chemical Research (RIKEN), on behalf of the
international Markarian 421 campaign team, communicate: "During the
intensive multifrequency campaign of this BL Lac object, ASCA
detected a flare from the source on Apr. 27. The preliminary
energy flux was 3.4 x 10E-10 erg cmE-2 sE-1 (2-10 keV), which is
about the same as the peak flux that we observed in the 1994
x-ray/TeV flare (Takahashi et al. 1996, Ap.J. 470, L89). The
photon index was about 2.5. A 7-day continuous observation with
ASCA began on Apr. 23. The preliminary analysis for the data taken
since Apr. 23 shows that the source is quite bright (2.1 and 2.5 x
10E-10 erg cmE-2 sE-1 on Apr. 24 and 25, respectively, at 2-10 keV).
The reports from the CAT, HEGRA, and Whipple teams (based on their
preliminary data analyses) tell us that Mrk 421 was very active
during this period also in TeV gamma-rays, with a strongly variable
flux with an average value around 1 Crab or so. Observations at
other wavelengths are encouraged. For more details of the campaign
schedule, send e-mail to takahasi@astro.isas.ac.jp; for current
activities of the optical monitoring during the campaign, see
http://gamma.bu.edu/webt/mrk421.html."
(C) Copyright 1998 CBAT
1998 April 28 (6888) Daniel W. E. Green
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