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IAUC 7322: BL Lac; 1998S

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                                                  Circular No. 7322
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)

     F. Montagni, E. Massaro, and R. Nesci, Istituto Astronomico,
Universita 'La Sapienza', Rome; G. Tagliaferri, Brera Astronomical
Observatory; and G. Tosti, Astronomical Observatory, Perugia
University, report that BL Lac is again at a brightness level
comparable to the maximum reached during the large 1997 outburst:
Nov. 27.75 UT, V = 13.4 +/- 0.03; 28.75, 13.0 +/- 0.03.  Further
multifrequency observations are encouraged.  A BeppoSAX observation
of BL Lac is scheduled between Dec. 5.455 and 6.729.

     S. D. Van Dyk, IPAC, California Institute of Technology; C. K.
Lacey, Naval Research Laboratory; R. A. Sramek, National Radio
Astronomy Observatory; and K. W. Weiler, Naval Research Laboratory,
report the detection of radio emission from the type-IIn supernova
1998S (IAUC 6829, 6830) with the Very Large Array:  "A radio-flux
density of 0.954 +/- 0.055 mJy at 8.435 GHz (wavelength 3.6 cm) and
1.098 +/- 0.075 mJy at 4.860 GHz (wavelength 6.2 cm), both on Oct.
28 in BnA configuration, was measured at the following position:
R.A. = 11h46m06s.140, Decl. = +47o28'55".45 (equinox 2000.0; +/-
0".2 in each coordinate).  This is in close agreement with the
reported optical position (end figures 06s.18, 55".5; IAUC 6831).
Previous observations indicate that the supernova was not radio
detectable at 8.435 GHz on 1999 June 17, to a limit of < 0.180 mJy
(3 sigma).  A list of radio observations, including non-detection
upper limits, is available at
http://rsd-www.nrl.navy.mil/7214/weiler/sne-home.html.  Filippenko
and Moran (IAUC 6830) predicted radio and x-ray emission from SN
1998S due to spectral evidence, resembling that of the type-IIn SN
1997eg, for strong interaction between the ejecta and circumstellar
material.  Although the stage of radio evolution is yet to be
determined, at an age of about 600 days on Oct. 28, the 6-cm
spectral luminosity (for a distance of 17 Mpc; Tully 1988, Nearby
Galaxies Catalogue) for SN 1998S of 4 x 10**26 erg s**-1 Hz**-1 is
already about 3 times brighter than the well-studied type-IIL SN
1980K at its 6-cm peak flux density.  For comparison with other,
well-studied type-IIn radio supernovae, SN 1998S is about 5 (SN
1988Z) to 10 (SN 1986J) times less luminous at 6 cm at a similar
age.  Neither SN 1988Z nor SN 1986J peaked at 6 cm until well
after 1000 days of age, so that SN 1998S may still be brightening
at cm wavelengths.  Detectable radio emission has been found to be
closely related to x-ray and late-time optical detectability, so
that further multi-wavelength observations are encouraged."

                      (C) Copyright 1999 CBAT
1999 November 29               (7322)            Daniel W. E. Green

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