PESSTO monitoring of SN 2012hn: further heterogeneity among faint Type I supernovae

S. Valenti, F. Yuan, S. Taubenberger, K. Maguire, A. Pastorello, S. Benetti, S. J. Smartt, E. Cappellaro, D. A. Howell, L. Bildsten, K. Moore, M. Stritzinger, J. P. Anderson, S. Benitez-Herrera, F. Bufano, S. Gonzalez-Gaitan, M. G. McCrum, G. Pignata, M. Fraser, A. Gal-YamL. Le Guillou, C. Inserra, D. E. Reichart, R. Scalzo, M. Sullivan, O. Yaron, D. R. Young

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Abstract

We present optical and infrared monitoring data of SN 2012hn collectedby the Public European Southern Observatory Spectroscopic Survey forTransient Objects. We show that SN 2012hn has a faint peak magnitude(MR ˜ -15.65) and shows no hydrogen and no clearevidence for helium in its spectral evolution. Instead, we detectprominent Ca II lines at all epochs, which relates this transient topreviously described `Ca-rich' or `gap' transients. However, thephotospheric spectra (from -3 to +32 d with respect to peak) of SN2012hn show a series of absorption lines which are unique and a redcontinuum that is likely intrinsic rather than due to extinction. Linesof Ti II and Cr II are visible. This may be a temperature effect, whichcould also explain the red photospheric colour. A nebular spectrum at+150 d shows prominent Ca II, O I, C I and possibly Mg I lines whichappear similar in strength to those displayed by core-collapsesupernovae (SNe). To add to the puzzle, SN 2012hn is located at aprojected distance of 6 kpc from an E/S0 host and is not close to anyobvious star-forming region. Overall SN 2012hn resembles a group offaint H-poor SNe that have been discovered recently and for which aconvincing and consistent physical explanation is still missing. Theyall appear to explode preferentially in remote locations offset from amassive host galaxy with deep limits on any dwarf host galaxies,favouring old progenitor systems. SN 2012hn adds heterogeneity to thissample of objects. We discuss potential explosion channels includingHe-shell detonations and double detonations of white dwarfs as well aspeculiar core-collapse SNe.
Original languageEnglish
Pages (from-to)1519-1533
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society, Volume 437, Issue 2, p.1519-1533
Volume437
Issue number2
Early online date13 Nov 2013
Publication statusPublished - 11 Jan 2014

Keywords

  • supernovae: general
  • supernovae: individual: 2012hn

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