Central Bureau Electronic Telegrams, 2799, 2 (2011/August-0)
Supernova 2011fh in NGC 4806.
PRIETO J.L. and SETH K.
Abstract (from CDS):
J. L. Prieto, Carnegie Observatories, reports than an optical spectrum (range 370-930 nm; resolution 0.7 nm) of 2011fh was obtained on Aug. 29.0 with the du Pont 2.5-m telescope (+ WFCCD) at Las Campanas Observatory. The spectrum has a blue continuum and strong emission lines from the Balmer series that show multiple velocity components, which are characteristic of type-IIn supernovae. The H-alpha profile can be well-fitted with three Gaussian components, including a narrow unresolved component and two relatively broad resolved components with FWHM = 1600 and 7400 km/s. Analysis of archival pre-explosion Spitzer/IRAC 3.6- and 4.5-micron images of the host galaxy (NGC 4806), obtained in 2009 Aug. and Sept. (Program ID 60007, PI K. Seth) show a mid-infrared point source at the position of 2011fh with flux densities 0.12 mJy (mag 15.9) at 3.6 microns and 0.11 mJy (mag 15.5) at 4.5 microns. At the distance of NGC 4806 (via NED; 33 Mpc from Virgo-infall corrected velocity), these values imply luminosity densities of 3.5 x 10**6 and 2.5 x 10**6 solar luminosity at 3.6 and 4.5 microns, respectively. If this is a single source, it would imply a very massive progenitor star. However, note that the spatial resolution of the Spitzer/IRAC images is approximately 260 pc (FWHM) at the distance of NGC 4806, and this source could be an H II region.