Discovery of a Supernova in NGC 3504

The two images below show our discovery of a supernova slightly below the nucleus in the galaxy NGC 3504.

These two J band images show the nuclear region of NGC 3504, the left one taken May 1996 at the KPNO 2.1m telescope (Elmegreen et al. 1997, AJ, 114, 1850), and the right one taken 2.38 March 1998 UT at NASA's Infrared Telescope Facility. We estimate the the supernova to be J = 14.5, K = 12.8. The following position was estimated from the J image: R.A. = 11h00m29.3s +/- 0.3", Decl. = +28o14'23" +/- 0.3" (equinox 1950 ) which is about 5.0" south and 0.8" east of the nucleus. This position assumes that the center of NGC 3504 is at R.A. = 11h00m28.4s, Decl. = +28o14'28" (equinox 1950, Basso et al. 1990, A&AS, 83, 569). The the pixel scales are 0.2 and 0.3 arcsec/pixel for the left and right images respectively. The point spread function of both images is similar. We thank D. Elmegreen for allowing us to use her J & K band images.

Apparently independent discovery reports of a supernova in NGC 3504 have been received (both from observations made at Mauna Kea) from Eric Emsellem, Observatoire de Lyon, via CCD images obtained on Mar. 31.272 UT at the Canada-France-Hawaii Telescope (CFHT), and from Geoffrey Clayton and Karl Gordon, Louisiana State University, via separate J, H, and K images taken on Mar. 2.38 with the NASA Infrared Telescope Facility. Emsellem notes that the star is located at R.A. = 11h03m11s.21, Decl. = +27o58'21".0 (equinox 2000.0), which is 0".6 east and 5".3 south of the center of NGC 3504. Clayton provides position end figures 12s.01, 13".2. Emsellem calculates that the object had a flux of 6.7 x 10^-16 erg s^-1 cm^-2 A^-1 at 900 nm on Mar. 31, and he roughly estimates I about 15. Clayton reports J = 14.5, K = 12.8 for Mar. 2. The star was not present in January, when a K observation of NGC 3504 was obtained with the CFHT Adaptive Optics Bonnette, and it is not present in other archival images, including JHK images taken in May 1996 at the Kitt Peak 2.1-m telescope (Elmegreen et al. 1997, A.J. 114, 1850) and in Dec. 1997 at Mt. Laguna Observatory. Note that this galaxy contains an apparent double nucleus, as well. P. Garnavich, Harvard-Smithsonian Center for Astrophysics, reports that inspection of a spectrum (range 840-900 nm) taken with the CFHT integral spectrograph OASIS on Mar. 31.312 (and provided by Emsellem) reveals what appears to be a broad Ca II P-Cyg profile characteristic of a supernova.

S. Ryder, Joint Astronomy Centre, reports that he obtained images in J, H, and K of the nucleus of NGC 3504 on Apr. 23.3 UT with the U.K. Infrared Telescope (+ IRCAM3). These show SN 1998cf (cf. IAUC 6914) at J = 14.9, H = 14.4, and K = 14.2, indicating that it was already fading in the near-infrared.

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