Central Bureau for Astronomical Telegrams
IAUC 6794: 1997eg; GRB 971214
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Circular No. 6794
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1997eg IN NGC 5012
A. V. Filippenko and A. J. Barth, University of California at
Berkeley, report: "A spectrum (range 430-680 nm, resolution 0.5 nm)
obtained on Dec. 20 with the Keck-2 telescope reveals that SN
1997eg (cf. IAUC 6790) is a peculiar type-II supernova. The
spectrum contains strong emission lines superposed on a
featureless blue continuum. Although generically referred to as
'type IIn' supernovae, this object is most similar to the subset
whose prototype is SN 1988Z (e.g., MNRAS 250, 786, and 262, 128).
H-alpha has three strong components: unresolved (FWHM < 200 km/s),
intermediate (FWHM about 2000 km/s), and broad (FWHM about 12 000
km/s). The broad He I 587.6-nm emission line is nearly as strong
as the corresponding component of H-alpha, suggesting a very high
helium abundance. The unresolved lines come from a very dense
circumstellar medium (n >/approx. 10**8 cmE-3): the [O III] 436.3-nm
emission is roughly as strong as [O III] at 500.7 nm. Moreover,
they are characterized by very high excitation: He II 468.6-nm and
[Fe X] 637.5-nm are prominent. Based on the behavior of previous
examples of this rare subset of type-IIn supernovae, we predict
that SN 1997eg will become very luminous at x-ray and radio
wavelengths due to strong interaction between the ejecta and
circumstellar material."
GRB 971214
E. Waxman, Institute for Advanced Study, Princeton, writes:
"The data of the detected optical and x-ray afterglow from GRB
971214 (IAUC 6787-6791 and references therein, plus private comm.
by L. Piro et al.) were used to make approximate predictions for
its behavior at different wavelengths, which may be useful in
planning observations. The detected flux reported in the first two
days of observations is consistent with general fireball-model
predictions, yielding optical-band magnitudes predicted by m_o + 3
log t, where t is measured in days and m_o = 24.6 for B, 23.4 for
V, 22.9 for R, 22.1 for I, and 21.1 for J. The x-ray flux is
predicted at about 4 keV by 5 x 10E-13 (t)E-1.2 erg sE-1 cmE-2.
Simultaneous observations at different optical colors (and at x-
rays) would provide strong constraints on the model. There is some
indication for extinction at the source (incorporated in the above
numbers); if real, it implies that absorption lines should be
detected (EW about 0.004 nm for Mg II), with the equivalent width
significantly changing on timescales of about 1 day -- and spectra
taken at different times would therefore be useful. Monitoring of
optical fluxes on < 1-day timescales would also be useful in
constraining fireball characteristics."
(C) Copyright 1997 CBAT
1997 December 20 (6794) Daniel W. E. Green
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