Ny lyssterk supernova SN 2004et i NGC 6946

Melding fra vsnet-alert@kusastro.kyoto-u.ac.jp 29. september 2004 kl 16:46 norsk tid.
Emne: [vsnet-campaign-sn 988] SN 2004et in NGC 6946 (mag 12.8, CBET 95)
SN2004et 20040927.0 128C SMr
SN 2004et (20:35:25.4, +60:07:17.6 (J2000.0), offset about 250"E and 120"S) is hosted by NGC 6946, a quite nearby (5.1Mpc) face-on spiral (SAB(rs)cd) galaxy in the northern part of the constellation Cygnus. NGC 6946 is one of the most SN productive galaxies (SNe 1917A, 1939C, 1948B, 1968D, 1969P, 1980K and 2002hh), then SN 2004et is the eighth SN in one galaxy (new record!). The Asiago team took a high-resolution spectrum on Sept. 28, which suggests that it is a young type II SN, affected some reddening by both in our Galaxy and in NGC 6946; total amount of E(B-V) is estimated as 0.41 mag. The discovery magnitude is consistent with the expected maximum for typical SN II. Further observations are strongly encouraged.

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Melding fra IAU 29. september 2004
SUPERNOVA 2004et IN NGC 6946
     T. Zwitter, University of Ljubljana; and U. Munari, Astronomical Observatory, Padova, report the discovery by S. Moretti, on unfiltered CCD images taken on Sept. 27 with a 0.4-m telescope at Ravenna, of a bright supernova (mag 12.8) in NGC 6946.   The new object is located at R.A. = 20h35m25s.4, Decl. = +60o07'17".6 (equinox 2000.0).  A high-resolution spectrogram, secured on Sept. 28 with the echelle spectrograph at the 1.82-m telescope in Asiago, shows a relatively featureless spectrum with a very broad, low-contrast H_alpha emission.  Sharp interstellar Na I absorption lines are observed at heliocentric radial velocities of -21.1 (+/- 0.7) and +45.2 (+/- 0.4) km/s, matching expectation for separate origin within our galaxy and NGC 6946.   The equivalent width of Na I D2 lines corresponds to a total reddening of E(B-V) = 0.41 mag, following the calibration by Munari and Zwitter (1997, A.Ap. 318, 269).

NOTE: These 'Central Bureau Electronic Telegrams' are intended to be preliminary announcements of items that later appear in the formal IAU Circulars.  Citations should normally be made to IAUCs rather than to CBETs.
(C) Copyright 2004 CBAT 2004 September 29                  (CBET 95)                Daniel W. E. Green

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Foreløpige kart uten sammenligningsstjerner (laget med SkyMap Pro 6.0) :

SN2004et_0.gif (Oversiktskart)

SN2004et_1.gif (Lm = 10.0 mag)

SN2004et_2.gif (Lm = 12.0 mag)

SN2004et_3.gif (Lm = 14.0 mag)

Offisielt godkjent kart med sammenligningsstjerner (laget med SkyMap Pro 6.0) :

SN2004et_e.gif (Lm = 14.5 mag.)

I følge SkyMap Pro 6 har NCG 6946 en samlet lysstyrke på 8.8 mag., men en overflatelysstyrke på bare 14.0 mag./kvadratbueminutt. Den er derfor ikke noe lett objekt selv med ganske store kikkerter. Supernovaen, med en lysstyrke på 12.8 mag C, skulle derimot være synlig i middels store amatørteleskop dersom forholdene er gode og du er langt unna sjenerende bylys.

B. Andresen. Trondheim Astronomiske Forening
4. okt. 2004