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IAUC 7587: Prob. RADIO SN IN NGC 7469

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                                                  Circular No. 7587
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
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PROBABLE RADIO SUPERNOVA IN NGC 7469
     L. Colina, Instituto de Fisica de Cantabria, Consejo Superior
de Investigaciones Cientificas (CSIC); A. Alberdi, Instituto de
Astrofisica de Andalucia, CSIC; J. M. Torrelles, Institut d'Estudis
Espacials de Catalunya, CSIC; N. Panagia, European Space Agency and
Space Telescope Science Institute; and A. S. Wilson, University of
Maryland, report the detection of an apparent bright radio
supernova on 2000 Oct. 27 with the Very Large Array (VLA) in
configuration A:  "A 3.6-cm flux density of 1.60 +/- 0.01 mJy/beam
is measured at R.A. = 23h00m44s.30, Decl. = +8 36'16".2 (equinox
1950.0).  The new radio object is located 1".65 west of the nucleus
and within the starburst ring of the bright Seyfert 1 galaxy NGC
7469.  Additional data taken with the VLA on 2001 Feb. 13 show that
the apparent radio supernova is still bright, with a 3.6-cm flux
density similar to that measured on 2000 Oct. 27.  The object was
not present in radio observations obtained in Sept. 1999 (5-sigma
limit of 0.1 mJy).  The only known cause of such a luminous radio
source is a supernova.  Radio monitoring is continuing."
     W. D. Li, R. Chornock, and A. V. Filippenko, University of
California at Berkeley, report: "NGC 7469 was extensively monitored
during the course of LOSS and LOTOSS (cf. IAUC 6627, 7126, 7514).
After subtracting a template image observed on 2000 Aug. 9.4 UT,
the KAIT images observed from 2000 Aug. 12.3 to Dec 25.1 all showed
an apparent 'residual' at R.A. = 23h03m15s.62 +/- 0s.03, Decl. =
+8 52'26".5 +/- 0".3 (equinox 2000.0), which is within 0".5 of the
optical nucleus of NGC 7469 and is about 2".6 east of the probable
radio supernova.  Selected unfiltered photometry for the residual
object:  2000 Aug. 12.3, 17.8; Sept. 18.2, 17.1; Oct. 1.2, 17.2;
7.2, 16.7; 15.2, 16.3; 19.2, 16.1; 24.2, 14.9; Nov. 12.2, 15.0;
17.2, 15.7; 23.1, 16.4; 28.2, 16.7; Dec. 25.1, 17.4.  Though the
residual brightened about 3 mag from Aug. 12.3 to Oct. 24.2, the
brightness of the nucleus of NGC 7469 changed by only about 0.2 mag
(from 13.0 to 12.8).  The light curve of the optical residual does
not look like any known type of supernova.  Because of the apparent
offset of the optical residual from the probable radio supernova,
and the fact that NGC 7469 is a well-known variable Seyfert galaxy
(e.g., Merkulova 2000, A.J. 119, 631), we suspect that the optical
residual we detected is caused by the variability of the central
AGN, rather than an optical counterpart of the reported radio
supernova.  Nevertheless, it is interesting to note that the
optical residual peaked at about Oct. 24, 3 days before the first
detection of the probable radio supernova.  Spectra of the nucleus
of NGC 7469 were taken with the Lick Shane 3-m telescope on 2000
Nov. 29, Dec. 5, and Dec. 21, and no apparent supernova feature was
detected."

                      (C) Copyright 2001 CBAT
2001 February 22               (7587)            Daniel W. E. Green

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