SN 2012ca: a stripped envelope core-collapse SN interacting with dense circumstellar medium \thanks{Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of programme 188.D-3003 (PESSTO).}
S. J. Smartt$^{1}$
R. Scalzo$^{2}$
M. Fraser$^1$
A. Pastorello$^3$
M. Childress$^2$
\newauthor G. Pignata$^4$
A. Jerkstrand$^1$
R. Kotak$^1$
S. Benetti$^3$
M. Della Valle$^{5,6}$
A. Gal-Yam$^7$
\newauthor P. Mazzali$^{8,3,9}$
K. Smith$^1$
M. Sullivan$^{10}$
S. Valenti$^{11,12}$
O. Yaron$^7$
D. Young$^1$ \newauthor and D. Reichart$^{13}$
$^{1}$Astrophysics Research Centre
School of Mathematics and Physics
Belfast BT7 1NN
UK
$^{2}$Research School of Astronomy and Astrophysics
Weston Creek
ACT 2611
Australia
$^{3}$INAF - Osservatorio Astronomico di Padova
Vicolo dell'Osservatorio 5
I-35122 Padova
Italy
$^{4}$Departamento de Ciencias Fisicas
Universidad Andres Bello
Avda. Republica 252
Santiago
Chile
$^{5}$INAF - Osservatorio astronomico di Capodimonte
Salita Moiariello 16
I- 80131 Napoli
$^{6}$International Centre for Relativistic Astrophysics
Piazzale della Repubblica 2
65122 Pescara
$^{7}$Benoziyo Center for Astrophysics
76100 Rehovot
Israel
Liverpool
$^{9}$Max-Planck Institut f\"ur Astrophysik
Karl-Schwarzschildstr. 1
D-85748 Garching
Germany
$^{10}$School of Physics and Astronomy
Southampton
SO17 1BJ
$^{11}$Las Cumbres Observatory Global Telescope Network
6740 Cortona Dr
Suite 102
Goleta
CA 93117
USA
$^{12}$Department of Physics
Santa Barbara
Broida Hall
Mail Code 9530
CA 93106-9530
Campus Box 3255
Chapel Hill
NC 27599-3255
We report optical and near-infrared observations of SN2012ca with the Public ESO Spectroscopy Survey of Transient Objects (PESSTO), spread over one year since discovery. The supernova (SN) bears many similarities to SN1997cy and to other events classified as Type IIn but which have been suggested to have a thermonuclear origin with narrow hydrogen lines produced when the ejecta impact a hydrogen-rich circumstellar medium (CSM). Our analysis, especially in the nebular phase, reveals the presence of oxygen, magnesium and carbon features. %The broad ejecta lines resemble those seen in %Type Ic SNe. This suggests a core collapse explanation for \ca, in contrast to the thermonuclear interpretation proposed for some members of this group. %Furthermore, \Ha\/ shows a narrow absorption component from a wind velocity %of a factor 2-3 greater than that likely exists in the CSM around SNe %Ia. %Because of a spectral similarity to stripped envelope SNe and the presence of H and He emission lines, we propose \ca\/ as SN Icn. We suggest that the data can be explained with a hydrogen and helium deficient SN ejecta (Type I) interacting with a hydrogen-rich CSM, but that the explosion was more likely a Type Ic core-collapse explosion than a Type Ia thermonuclear one. This suggests two channels (both thermonuclear and stripped envelope core-collapse) may be responsible for these SN~1997cy-like events. %We report optical and near infrared (NIR) observations of the % SN~1997cy-like event \ca\/, spread over one year since the % discovery, in order to characterise the supernova (SN). \ca\/ % belongs to the class of interacting SNe with a H- and He-rich % circumstellar material (CSM). The analysis, especially at nebular % phase, extended up to NIR wavelengths reveals presence of O, Mg and % C. This suggests a core collapse explanation for this event, in % contrast to the thermonuclear interpretation of these type of SNe. % Furthermore, \Ha\/ shows a narrow absorption component from a wind % of a factor 2-3 greater than that seen in the CSM around SNe %Ia. %Because of a spectral similarity to stripped envelope SNe and the presence of H and He emission lines, we propose \ca\/ as SN Icn. %\ca\/ core collapse nature provides evidence of a viable alternative %explanation to the interacting SN Ia for SN~1997cy-like events, %suggesting as two channels are responsible for such a scenario.
CI_2012ca_20130923.tex
% mn2esample.tex
%
% v2.1 released 22nd May 2002 (G. Hutton)
%
% The mnsample.tex file has been amended to highlight
% the proper use of LaTeX2e code with the class file
% and using natbib cross-referencing. These changes
% do not reflect the original paper by A. V. Raveendran.
%
% Previous versions of this sample document were
% compatible with the LaTeX 2.09 style file mn.sty
% v1.2 released 5th September 1994 (M. Reed)
% v1.1 released 18th July 1994
% v1.0 released 28th January 1994

\documentclass[useAMS,usenatbib]{mn2e}
\usepackage[T1]{fontenc}
\usepackage{aecompl}
% If your system does not have the AMS fonts version 2.0 installed, then
% remove the useAMS option.
%
% useAMS allows you to obtain upright Greek characters.
% e.g. \umu, \upi etc.  See the section on "Upright Greek characters" in
% this guide for further information.
%
% If you are using AMS 2.0 fonts, bold math letters/symbols are available
% at a larger range of sizes for NFSS release 1 and 2 (using \boldmath or

% preferably \bmath).
%
% The usenatbib command allows the use of Patrick Daly's natbib.sty for
% cross-referencing.
%
% If you wish to typeset the paper in Times font (if you do not have the
% PostScript Type 1 Computer Modern fonts you will need to do this to get
% smoother fonts in a PDF file) then uncomment the next line
% \usepackage{Times}

%%%%% AUTHORS - PLACE YOUR OWN MACROS HERE %%%%%
\usepackage{graphicx}
\usepackage{multirow}
%\usepackage{subfigure}
\usepackage{amssymb}
\usepackage{hyperref}
\hypersetup{colorlinks=false,
		linkcolor=black,
		urlcolor=cyan}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\title[SN 2012ca]{SN 2012ca: a stripped envelope core-collapse SN interacting with dense circumstellar medium 
\thanks{Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of programme 188.D-3003 (PESSTO).} }
\author[C. Inserra et al.]{C. Inserra$^{1}$\thanks{E-mail: c.inserra@qub.ac.uk(CI)},
S. J. Smartt$^{1}$, R. Scalzo$^{2}$, M. Fraser$^1$, A. Pastorello$^3$, M. Childress$^2$,
\newauthor G. Pignata$^4$, A. Jerkstrand$^1$, R. Kotak$^1$, S. Benetti$^3$, M. Della Valle$^{5,6}$, A. Gal-Yam$^7$,
\newauthor P. Mazzali$^{8,3,9}$, K. Smith$^1$, M. Sullivan$^{10}$, S. Valenti$^{11,12}$, O. Yaron$^7$, D. Young$^1$
\newauthor and D. Reichart$^{13}$\\
$^{1}$Astrophysics Research Centre, School of Mathematics and Physics, Queen's University
  Belfast, Belfast BT7 1NN, UK\\
$^{2}$Research School of Astronomy and Astrophysics, The Australian National University, Weston Creek, ACT 2611, Australia\\
$^{3}$INAF - Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova, Italy\\
$^{4}$Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago, Chile\\
$^{5}$INAF - Osservatorio astronomico di Capodimonte, Salita Moiariello 16, I- 80131 Napoli, Italy\\
$^{6}$International Centre for Relativistic Astrophysics, Piazzale della Repubblica 2, 65122 Pescara, Italy\\
$^{7}$Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel\\
$^{8}$Astrophysics Research Institute, Liverpool John Moores University ,Liverpool, UK\\
$^{9}$Max-Planck Institut f\"ur Astrophysik, Karl-Schwarzschildstr. 1, D-85748 Garching, Germany\\
$^{10}$School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK\\
$^{11}$Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr, Suite 102, Goleta, CA 93117, USA\\
$^{12}$Department of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara, CA 93106-9530, USA\\
$^{13}$University of North Carolina at Chapel Hill, Campus Box 3255, Chapel Hill, NC 27599-3255, USA}

\def\kms{km\,s$^{-1}$}
\def\Ha{H{$\alpha$}}
\def\Hb{H{$\beta$}}
\def\Hg{H{$\gamma$}}
\def\ni{$^{56}$Ni}
\def\co{$^{56}$Co}
\def\fe{$^{56}$Fe}
\def\mcento{mag\,(100d)$^{-1}$}
\def\M{M$_{\odot}$}
\def\R{R$_{\odot}$}
\def\ebv{E(B--V)}
\def\ca{SN2012ca}

\begin{document}

\date{Received.....; accepted...........}

\pagerange{\pageref{firstpage}--\pageref{lastpage}} \pubyear{}

\maketitle

\label{firstpage}

\begin{abstract}

  We report optical and near-infrared  observations of 
  SN2012ca with the Public ESO Spectroscopy Survey of Transient Objects (PESSTO), spread over one year since 
  discovery. The supernova (SN) bears many similarities to SN1997cy and 
to other events classified as Type IIn but which have been 
suggested to have a thermonuclear origin with narrow hydrogen
lines produced when the ejecta impact a hydrogen-rich circumstellar
medium (CSM). Our analysis, especially in the nebular
  phase, reveals the presence of oxygen, magnesium and carbon 
  features. %The broad ejecta lines resemble those seen in
  %Type Ic SNe. 
  This suggests a core collapse explanation for \ca, in
  contrast to the thermonuclear interpretation proposed for some members of this group.
  %Furthermore, \Ha\/ shows a narrow absorption component from a wind velocity
  %of a factor 2-3 greater than that likely exists in the CSM around SNe
  %Ia. %Because of a spectral similarity to stripped envelope SNe and the presence of H and He emission lines, we propose \ca\/ as SN Icn.
We  suggest that the data can be explained with a hydrogen and helium
deficient SN ejecta (Type I) interacting with a hydrogen-rich CSM, 
but that the explosion was more likely a Type Ic core-collapse explosion
than a Type Ia thermonuclear one. This suggests 
 two channels (both thermonuclear and stripped envelope core-collapse) may be responsible for these SN~1997cy-like 
events. 


%We report optical and near infrared (NIR) observations of the
 % SN~1997cy-like event \ca\/, spread over one year since the
 % discovery, in order to characterise the supernova (SN). \ca\/
 % belongs to the class of interacting SNe with a H- and He-rich
 % circumstellar material (CSM). The analysis, especially at nebular
 % phase, extended up to NIR wavelengths reveals presence of O, Mg and
 % C. This suggests a core collapse explanation for this event, in
 % contrast to the thermonuclear interpretation of these type of SNe.
 % Furthermore, \Ha\/ shows a narrow absorption component from a wind
 % of a factor 2-3 greater than that seen in the CSM around SNe
  %Ia. %Because of a spectral similarity to stripped envelope SNe and the presence of H and He emission lines, we propose \ca\/ as SN Icn.
  %\ca\/ core collapse nature provides evidence of a viable alternative
  %explanation to the interacting SN Ia for SN~1997cy-like events,
  %suggesting as two channels are responsible for such a scenario.


 \end{abstract}
 
\begin{keywords}
supernovae: general -- %supernovae: individual: SN~2012ca -- 
supernovae: circumstellar interaction
\end{keywords}

\section{Introduction}\label{sec:intro}

Supernovae (SNe) are produced by two physical mechanisms:
thermonuclear SNe (SN Ia) which completely destroy the degenerate
progenitor star \citep{hn00}, and core-collapse SNe (CC-SNe) which
leave a compact remnant \citep{2012ARNPS..62..407J}. Thermonuclear SNe
can be produced through a single-degenerate channel when a white
dwarf accretes hydrogen and helium from a companion or through the
merger of two WDs \citep{hn00}. CC-SNe are produced by the explosion following the
gravitational collapse of the cores of massive stars and classified
according to the presence (SNe II) or absence (SN I) of H and/or He in
their spectra \citep{fi97}. Theoretical stellar evolution calculations
have long attempted to link evolved model stars
\citep{he03,2012ARA&A..50..107L} to the types of CC-SNe observed and
in some cases the directly identified progenitors
\citep{2009ARA&A..47...63S}. The two physical mechanisms are rather
different, but a number of SNe have been discovered for which 
 the underlying origin of the explosion is unclear. 

Events such as SN~2002ic \citep{ha03,de04,wv04} and PTF11kx
\citep{di12,si13a}, exhibit unambiguous signs of the ejecta
interacting with circumstellar material (CSM). They have been
classified as interacting Type Ia SNe and are thought to be of
thermonuclear origin. Their spectra appear to be a``diluted'' spectrum
of a bright SN Ia (e.g. SNe 1991T and 1999aa) along with superimposed  H
emission lines. PTF11kx shows the strongest evidence
for being a thermonuclear event interacting with CSM expelled by a
companion red giant star \citep{di12}. %\citep{di12,si13a}. 
However the physical
origin of other SNe are still uncertain and this debate dates back to
the peculiar Type IIn SN1997cy \citep{ge00,tu00}. The growing
arguments that many such events with narrow hydrogen (classified as
SNe IIn) could be thermonuclear has resulted in SN2008J \citep{ta12}
being labelled as an interacting SN Ia, while new data
for SN2005gj \citep{al06,pr07} has been used to suggest a 
thermonuclear origin rather than a CC-SN \citep{si13b}.  But this is not
the unanimous view, with \citet{be06} and \citet{tr08} 
arguing for a core-collapse origin for SNe 2002ic and 2005gj, respectively. 

These ambiguous and interacting events are important for
determining the possible progenitor channels for SNe Ia in particular,
but are rare. During the first run of the Public ESO Spectroscopy Survey of Transient Objects (PESSTO)\footnote{www.pessto.org} in
April 2012, SN2012ca was classified as an unusual Type IIn, with an
early spectral resemblance to SN~1997cy. Its distance and brightness
have allowed an extensive follow-up until late epochs providing
another object to better understand whether these events are all
interacting SNe Ia or some are in fact CC-SNe. The letter presents
most of the first season of PESSTO optical and NIR data, which is
publicly available in the ESO\footnote{as part of the Spectroscopic Survey Data Release 1 
(SSDR1)} and WISeREP\footnote{http://www.weizmann.ac.il/astrophysics/wiserep/} \citep{ya12} archives. 

 %We also analyse and discuss the peculiar class of SN~1997cy-like events.
%, pointing strongly toward a core collapse scenario for \ca\/ and proposing the SNe Ic interacting scenario (SNe Ic-CSM) as the best competitor of that involving Type Ia.




\section{Observations and data analysis}\label{sec:obs}

\ca\/ was discovered in the late-type spiral galaxy ESO 336-G009 by
\citet{dr12}, with a first detection on 2012 April 25.6 UT
(m$_r\sim$14.8 mag). A spectrum was obtained at the New Technology
Telescope (NTT) + EFOSC2 \citep{va12,in12} on April 29.4 as part of
PESSTO. The initial spectrum of \ca\/ showed a resemblance to a few
SNe 1997cy-like explosions at $\sim$60 d post maximum. Because of the lack of
early data, we cross-correlated the first spectrum with a library of
SN 1997cy-like events at multiple epochs
and found a best match adopting a peak light epoch at  MJD $55988.0\pm9.0$ (March 2).
% finding a best match with a
%peak light epoch at MJD $55988.0\pm9.0$ (March 1). 
From the emission
component of the Balmer lines a redshift $z=0.019$ was measured,
consistent with that of the host galaxy. Adopting a standard cosmology
with $H_0 = 72$ \kms\/, $\Omega_{\rm M}=0.27$ and $\Omega_{\rm
  \lambda}=0.73$, NED\footnote{NASA/IPAC Extragalactic Database}
provides $\mu=34.54\pm0.15$ mag from the heliocentric radial velocity of
$v_{\rm host}=5834\pm37$ \kms\/, which will be used throughout the
letter. There is no detection of Na~{\sc i} interstellar medium (ISM)
features from the host galaxy, nor do we have any evidence of
significant extinction inside the host from the SN spectra itself.
This suggests that the internal absorption  is low and we assume it to be  
negligible. Moreover, \ca\/ is 3.5 kpc far from the centre of the host galaxy, 
this is consistent with the absence of significant extinction. The Galactic reddening
toward the SN line of sight is $E(B-V)=0.06$ mag \citep{sf11}, which
we correct for in the following.
%Here we present a limited set of optical and infrared observations, spread over one year, to characterise the SN. 
%Full coverage of the SN will be published in a future paper.
%Spectro-photometric follow-up was obtained by PESSTO with NTT+EFOSC2 ($Ugriz$ and $\#GR13$), PROMPT \citep[$BgVrRiIz$;][]{re05}, Swift+UVOT and ANU+WiFeS in optical, while in near infrared (NIR) with NTT+SOFI (BG,RG).
Spectro-photometric follow-up was obtained by PESSTO with NTT+EFOSC2, PROMPT \citep[][]{re05}, Swift+UVOT and ANU+WiFeS in optical, while in near infrared (NIR) with NTT+SOFI.
Images and spectra
were reduced in the standard fashion, and the NTT data 
were processed within the PESSTO pipeline as  in \citet{va13,fr13}.
% \citep[see][ for more details on the reduction process]{va13,fr13}. 
%For NIR spectroscopy, solar analogues were observed at a similar airmass to the target. This allowed us to flux calibrate the spectra and remove strong features due to telluric absorption.
The resolution of the optical spectra were checked and found to be
$\sim$18 \AA\/ and $\sim$2 \AA\/ for the EFOSC2 and WiFeS data,
respectively. The resolution in the NIR were $\sim$23 \AA\/ (blue grism) and $\sim$33 \AA\/ (red grism). %for {\bf the blue and red grism}, respectively. 

% using the PESSTO pipeline\footnote{The PESSTO pipeline has been developed by S. Valenti, and
%comprises a set of {\sc python} scripts which call pyraf tasks (the {\sc python} version of {\sc iraf}) to reduce
%EFOSC2 and SOFI data following the standard prescription.}, which also subtracts a smoothed fringe frame in the $i$-band.
%Spectra were reduced (including trimming, overscan, bias
%correction and flat-fielding) using standard routines within
%{\sc iraf}\footnote{{\sc iraf} is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with
%the National Science Foundation.} (and pyraf). Optimal extraction of the spectra was adopted to improve the
%final signal-to-noise (S/N) ratio. Wavelength calibration was performed
%using spectra of comparison lamps acquired with the same
%configuration as the SN observations. Atmospheric extinction
%correction was based on tabulated extinction coefficients for each
%telescope site. Flux calibration was performed using
%spectro-photometric standard stars observed on the same nights with
%the same set-up as the SN. The data were corrected for telluric
%absorption by subtracting a model spectrum of the telluric
%bands \citep[see][ for more details on the reduction process]{fr13}.

%These steps are included in the PESSTO pipeline.
%The resolution of the optical spectra were checked and found to be
%$\sim$18\AA\/ and $\sim$2\AA\/ for the EFOSC2 and WiFeS data,
%respectively. While for the NIR were $\sim$23\AA\/ and $\sim$33\AA\/ for GB and GR, respectively. 
% corresponding to a resolution in velocity space of $\sim$800 \kms\/
% at \Ha\/ wavelength. For NIR spectroscopy, solar analogues at a
% similar airmass were observed either before or after \ca\/; these
% were used to calibrate in flux the spectra and
% to %facilitate the removal of the strong telluric absorptions.
% which lie between 1 and 2$\mu$m.
%The PESSTO raw data are publicly available in the ESO archive and the reduced
%spectra will be released through ESO as part of the Spectroscopic Survey Data Release 1 
%(SSDR1), and through WISeREP$^{2}$. 




\subsection{Bolometric luminosity}\label{ss:bol}
\begin{figure}
\includegraphics[width=\columnwidth,height=5.7cm]{bolom2.eps}
\caption{$Ugriz$ (optical) bolometric light curves of \ca\/, the Type
  Ic SN 1998bw \citep[{\it
    UBVRI};][]{ga98} %and 2007gr \citep[{\it UBVRI};][]{va08,hu09}
  , the bright Type Ia 1991T \citep[{\it UBVRI};][]{li98}, the
  Type Ia interacting PTF11kx \citep[$gri$;][]{di12,si13a} and SN
  2005gj \citep[{\it ugriz};][]{pr07}, the Type IIn 2010jl
  \citep[$UBVRI$;][]{zh12}, the Type Ibn SN 2006jc \citep[{\it
    UBVRI};][]{pas07} and the peculiar Type IIn SN 1997cy
  \citep[$BVRI$;][]{ge00,tu00}. %The pseudo-bolomeetric light curve were calculated from the published magnitudes.
  Phase is with respect to maximum light
  at rest-frame. The epochs of the SN~2012ca spectra reported are marked with
  vertical lines.
}
\label{fig:cfr_bol}
\end{figure}

\begin{figure}
\includegraphics[width=\columnwidth,height=6.0cm]{sp_evol2.eps}
\caption{Rest-frame sequence of spectra of \ca\/ until one year since discovery. 
Phases are since the estimated maximum epoch (phases since discovery are reported in parentheses). }
%The most prominent Balmer and He~{\sc i} features are indicated by vertical black dashed and blue dashed lines,
 %respectively. 
 %The presence of O (green dashed line) and C (orange dashed line) are features seen uniquely in CC-SNe.} 
\label{fig:spev}
\end{figure}

%In order to construct this,
%the broad band magnitudes in $Ugriz$ were converted into
%fluxes at the effective filter wavelengths, then were corrected for
%the adopted extinction. A SED was
%then computed over the wavelengths covered and the flux under the SED
%was integrated assuming there was zero flux beyond the integration
%limits. Fluxes were then converted to luminosities using the
%distance previously adopted.

A pseudo-bolometric light curve ($Ugriz$) of \ca\/ (Fig.~\ref{fig:cfr_bol}) was constructed
using similar methods as in \cite{in13}.
%{\bf For a calculation of a full bolometric lightcurve ideally one desires
%photometric coverage from around 2000\AA\ in the UV through to $K-$band, as most
%SNe in the first 100-200 days radiate the vast majority of their light
%in this regime. These extensive data sets are not available for
%our sample, hence we use the pseudo-bolometric light curve method
%which integrates flux from the $U$-band through to $z$-band. 
There is certainly flux outside these bands however, to first order we
assume that these contributions are similar in each SN. This allows
an approximate comparison of the pseudo-bolometric luminosities which
is not as comprehensive as full bolometric measurements, but better
than using single band comparisons.
Although there are uncertainties in the explosion date, peak epoch
and some caveats comparing pseudo-bolometric lightcurves determined using different optical filter systems,
\ca\/ appears brighter and more slowly declining than SN2005gj. It is
of comparable luminosity to SN1997cy between 60-250 d from peak, 
and also to the luminous Type IIn SN2010jl.
% However, suggesting that \ca\/ was possibly discovered soon before
% maximum light. That is also in agreement with the additional
% follow-up magnitudes reported by \citet{dr12}. These evidences and
% the similarity between the light curves strengthen the
% trustworthiness of the explosion epoch reported above. 
However it is significantly brighter and slower evolving than SNe 1991T (Ia) and 1998bw (Ic)
or the interacting Ibn SN2006jc. Indeed, \ca\/ appears to be 10
times more luminous than the bright SN Ic reported in Fig.~\ref{fig:cfr_bol},
and its overall evolution is much slower than that of normal Type Ic or Type Ia 
events. % probably due to interaction.
The post peak decline rate is $\gamma=0.5\pm0.1$ mag/100 d until the last
epoch available, and is much slower than those of the interacting SNe Ia
PTF11kx and SN2005gj and the Type Ibn 2006jc, with $\gamma\sim3.1$,
$\gamma\sim1.1$ and $\gamma\sim7.4$ mag/100d, respectively. The
decrease is slower than the \co\/ decay even at 250 d, suggesting that
the interaction is still the main energy source. One striking feature in Fig.~\ref{fig:cfr_bol}
is the self-similarity of \ca\/, SN1997cy, SN2005gj and how different they
appear compared to the initial decline of PTF11kx. While the PTF11kx decline 
$\gamma\sim0.5$ after 200 d is similar to that of \ca\/, the late-time values of the former
 are determined solely from $r$-band observations (assuming constant colours from neighbouring epochs) and show considerable scatter, 
 thus we suggest to treat this result with caution.


\subsection{Spectroscopy}\label{ss:sp}


Optical spectra of \ca\/ are shown in Fig.~\ref{fig:spev} to
illustrate the evolution during the first year. The somewhat blue
continuum does not show significant evolution, suggesting an
origin due to multiple, narrow lines of iron-group elements creating a
pseudo continuum \citep[][]{sm09,si13b}. After about 180 d the
pseudo-continuum seems visible only at wavelength shorter than
5500 \AA\/, whereas the features redward look nebular. Most notable in
\ca\/ is the presence of Balmer and He~{\sc i} emission lines through
its entire evolution. The high resolution of WiFeS allows us to
resolve narrow components in H lines. We see narrow P-Cygni absorption
in \Ha\/ from a wind, as shown in Fig.~\ref{fig:sptot} (right). The
expansion velocity of the absorption minimum is $200\pm90$ \kms\/ , a
factor 3 greater than that measured for PTF11kx \citep[65
\kms;][]{di12}. This is also a factor 2 or 3 greater than that observed in
probable diffuse CSM from the companion of an exploding WD in some
SNe Ia \citep[50-100 \kms;][]{pa11}. However, \citet{st11} noted that some higher velocities
(150-200 \kms) can be reached in the CSM of a small fraction of SNe Ia.
% The low resolution of $\#GR13$ does not allow us to resolve possible
% narrow components, indicative of the presence of a slowly expanding
% CSM. \Ha\/ and He~{\sc i} are unresolved with FWHM $\lesssim900$
% \kms\/ and $\lesssim800$ \kms\/, respectively.
A broader emission component is also identified for H and He~{\sc i}.
No P-Cygni profiles linked to this component are seen. % in He~{\sc i},
%whereas an absorption is seen on the blue side of \Ha\/, {\bf [COSIMO
%  - do you really mean H-alpha here, as I would be confused if you
%  did. You have already discussed the absorption component in H-alpha
%above, but now you are casting doubt upon it}. 
% but is likely
%due to a blending of different lines. 
The He~{\sc i} broader component
shows a FWHM velocity $\sim1800$ \kms\/, decreasing to $\sim1500$
\kms\/ in the last spectrum, while \Ha\/ has $v_{\rm
  FWHM}\sim3000-2200$ \kms\/ in the same period. This is also
confirmed by the measurement of the unblended NIR features (see
below). These broad lines can be associated with the fast-moving
ejecta or, in case of interaction such as in \ca\/, viable
explanations are boxy emission from interaction \citep{cf94} or
Thomson scattering of photons by electron in a dense CSM
\citep{ch01,de09}. From deblending  the Ca~{\sc ii} NIR
components, we measure a velocity of $\sim7000$ \kms\/ (at +198d)
related to the fast-moving ejecta, higher than those of H and He,
suggesting a different origin for those emission components.
%suggesting that some helium and hydrogen are accelerated by the interaction. 
%However, these velocities are lower than those of He~{\sc i} ($\sim2500$ \kms) in SN~2006jc \citep{pas07}. % and \Ha\/ ($\sim6000$ \kms) in SN~2009ip \citep{fr13}. 
%To our knowledge \ca\/ is the first SN of this type showing a somewhat broader He~{\sc i} component and an \Hb\/ emission component comparable to those of Type IIn SNe (cfr. Fig.~\ref{fig:spcmp} bottom).

\begin{figure*}
\includegraphics[width=18cm,height=5.7cm]{sp_tot4.eps}
\caption{Right: composite spectrum of \ca\/ from optical to NIR wavelengths, at $\sim$198-208 d post maximum ($\sim$143-153 d from discovery). %The spectra are corrected for Galactic reddening and reported at rest-frame. 
The $\oplus$ symbol marks the position of the strongest telluric absorption. The most prominent features are labelled. Right: temporal evolution of \Ha\/ from  162 d to 206 d post maximum. The vertical red dashed line marks the velocity of the CSM.} 
\label{fig:sptot}
\end{figure*}

A combined spectrum comprised of an optical and a blue NIR grism taken on Sept. 15, plus a red NIR grism taken on Sept. 24 is shown in Fig.~\ref{fig:sptot}.
As reported above, the optical region shows Balmer lines in emission, while the Paschen and Brackett series are visible at wavelengths $>8500$ \AA\/ with comparable velocities to the Balmer series at that phase ($v{\rm (Pa\alpha)}_{\rm FWHM}=v{\rm (H\alpha)}_{\rm FWHM}\sim2400$ \kms). He~{\sc i} $\lambda$5876, $\lambda$7065, $\lambda$10830 and $\lambda$20589 emission lines are clearly detected, and also tentatively at $\sim16800$~\AA\/. Calcium has also been identified with a weak Ca~{\sc ii} H\&K line, the Ca NIR triplet and the [Ca~{\sc ii}] $\lambda\lambda7291,7324$ doublet, implying that at 198d the SN is moving toward the nebular phase. 
Two puzzling lines at $\sim6250$~\AA\/ and $\sim7710$~\AA\/ are detected. They could be [O~{\sc i}] $\lambda\lambda$6300, 6364 and O~{\sc i} $\lambda$7774 (v$_{\rm FWHM}\sim7000$ \kms), but blue shifted by $\sim2500$~\kms\/. This hypothesis is strengthened by the presence of a line at $\sim7170$ \AA\/ identifiable as [O~{\sc ii}] blue shifted at the same velocity. The shift could be attributed to asymmetries in the ejecta or a clump moving toward us. Moreover, [O {\sc i}] $\lambda$5577 blue shifted by the same amount could be responsible for the red shoulder of the pseudo continuum.
%Another speculative explanation of the blue shift could be dust presence. However, it seems common for SN1997cy-like objects produce dust, likely in a cool dense shell, after 75-100d past maximum \citep{fo11,si13b}. 
%An alternative identification for the feature at $\sim6250$ \AA\/ is a blend of multiple Fe lines, while a blending of Mg~{\sc i} and Fe~{\sc i} lines could be responsible of the line at 7710 \AA\/.
%Indeed 
Metal lines of various species are unambiguously detected both in the optical and 
the NIR. Fe~{\sc ii} multiplet~42 %($\lambda\lambda4924, 5018, 5169$) 
is responsible for the features redder than \Hb\/.  Mg~{\sc i}] $\lambda$4571 is already seen at this phase and gives plausibility to the detection of [O~{\sc i}] because of their mutual presence in Type Ib/c SNe \citep[see][]{hu09}. Other Mg lines could explain the feature at $\sim4600$ \AA\/ in the first spectrum and at 11300 \AA\/ at $\sim198$d, whilst Mg~{\sc i} $\lambda$15024, the strongest Mg line in the NIR, is detected and we measured a FWHM velocity of $\sim$7000 \kms\/. % and thus related to the ejecta.
%The last line looks prominent since +160d and only Mg~{\sc i} and Fe~{\sc i} are present at that wavelength, thus the line could be a blending of these two ions. An alternative, speculative identification could be O~{\sc i} $\lambda$7774 that should be blue shifted because of dust presence. However, it seems common for SN1997cy-like objects produces dust, likely in a cool dense shell, after 75-100d past maximum \citep{fo11,si13b}. 
%However, no O~{\sc i} $\lambda9260$ or [O~{\sc ii}] $\lambda\lambda6300, 6364$ is detectable, weakening such identification. 
%In late spectra the Ca NIR triplet is weakened and [C~{\sc i}] at $\sim8700$~\AA\/ is shown in emission.
After 256~d the Ca NIR triplet is weaker, and [C~{\sc i}] at $\sim8700$~\AA\/ is shown in emission. The [C~{\sc i}] profile resembles 
those of typical SNe Ic after five months from peak \citep{fi97}.

%\begin{figure}
%\includegraphics[width=\columnwidth]{sp_cmp3.eps}
%\caption{Comparison of the +58d (top) and +198d (central) spectra with those of the Type Ibn SN 2006jc \citep[$\phi=+13$d;][]{pas07}, the Type Ia SN 1991T \citep[$\phi=+54$d and $\phi=+217$d;][]{si12}, the Type IIn 1988Z \citep[$\phi=+115$d;][]{tu93}, and the Type Ic SNe 1998bw \citep[$\phi=+130$d and $\phi=+201$d;][]{pa01} and 2007gr \citep[$\phi=+56$d; and $\phi=+158$d;][]{hu09}. Bottom: comparison of the first two spectra of \ca\/ with those of PTF11kx \citep[cyan, $\phi=+56$d and $\phi=+130$d from maximum;][]{di12} and SN 1997cy \citep[dark grey, $\phi=+100$d and $\phi=+224$ past GRB detection;][]{tu00}. Balmer and He~{\sc i} features are indicated by vertical black dashed and blue dashed lines, respectively. The spectra are corrected for Galactic reddening and reported at rest-frame. Phases are respect to maximum light.} 
%\label{fig:spcmp}
%\end{figure}

%In the upper panel of
% Fig.~\ref{fig:spcmp} %the comparison with the Type Ibn SN~2006jc highlights that the velocity of the He~{\sc i} emission lines is smaller than those of Ibn SNe \citep[$v$(He~{\sc i})$_{\rm FWHM}\sim2500-5000$ \kms;][]{pas07,pas08}.
% Also interesting is a comparison of \ca\/ with the Type Ic SN
% 1998bw, and the Type Ia 1991T at similar epochs is shown to
% investigate about possible spectral similitudes.
Since SNe Ia and Ic have similar spectral evolution during the
photospheric period and as a consequence it is not easy to detect
features uniquely seen in a class before $\sim$60~d post maximum
\citep{ta06}, especially if we take into account the interaction. In Fig.~\ref{fig:spcmp} we compare \ca\/ %late{\bf -time} 
spectra
with those of the bright  SNe 1998bw (Ic) and 1991T (Ia) at
similar epochs to investigate possible spectral similitudes.
% the first spectrum focusing on similitudes and differences between
% \ca\/ and these classes.
In the earliest spectrum of \ca\/ the blue region ($\lesssim5600$ \AA\/) %of the spectrum of \ca\/
appears more similar to SN~1998bw than SN~1991T both in continuum and
line profiles. In the region around \Ha\/ we cannot make a detailed
comparison because of the presence of the emission lines, however the
%strong 
Si~{\sc ii} and [Fe~{\sc ii}] %$\lambda\lambda$6451,6456
lines typical of Type Ia SNe are not consistent with the line profiles
seen in \ca\/, even after accounting for dilution by a
continuum. % (cfr. Fig.~\ref{fig:ncmp}).
%In Fig.~\ref{fig:ncmp} the normalised spectrum of \ca\/ at 160d is compared with diluted spectra of SNe 1998bw and 1991T to have a better insight into the origin of this puzzling event.
%In the central panel, the same SNe are used to further investigate the spectral behaviour at nebular phase.
In the nebular phase comparison, a SN Ia spectrum at a similar phase
to \ca\/ makes it difficult to explain the region bluer than 6500\AA\/
because of the presence of [Fe~{\sc ii}], [Fe~{\sc iii}] and [Co~{\sc
  ii}] lines in the
former. %Whereas Type Ic SNe, with the remarkable resemblance of SN~1998bw, are more similar to \ca\/ spectrum.
In contrast, \ca\/ bears more resemblance to
  SN1998bw. We suggest the emission features at 6250\AA\/ and 7710\AA\ are
  indeed [O~{\sc i}] which would make a Ia origin unlikely. While the
  features are not as broad and prominent as in SN1998bw, we suggest
  they are most likely to be [O~{\sc i}], and hence are important
  indications of a core-collapse origin. %{\bf
 % [COSIMO - I wouldn't say remarkable - 98bw looks broader lined,
 % large blueshifts in many lines. There is some resemblance, but not
 % ``remarkable''. Have you tried other type Ic comparisons e.g. 07gr which may have more comparable line widths.}
% {\bf Redwards} of \Ha\/, both SNe
  %Ic and Ia have the same lines, but the Ca NIR triplet velocity
  %seems more similar to that of SN~1998bw, a
  %similarity also observable for the other lines at optical
 % wavelengths. 
% {\bf Also noticeable is the similarity in the line profile with the bright Type IIP SN 2009dd.}
 In the bottom panel of Fig.~\ref{fig:spcmp} the
  difference between an interacting Type Ia and \ca\/ becomes clear,
  comparing the object to PTF11kx at similar
  epochs. %Assuming \ca\/ is at maximum light around the phase of the first spectrum, the two spectra differ by $\sim20$d.
  They show some %remarkable 
  dissimilarities, % at all wavelengths, 
  mainly due
  to the presence of strong metal lines such as Fe~{\sc ii} %and Si~{\sc iii} 
  in
  PTF11kx. %The \Ha\/ profile is also quite different and the contrast enhances comparing the two objects at peak, where the Balmer emission lines in PTF11kx are barely noticeable.
  The 198 d spectrum is more similar to that of SN1997cy at $\sim$224 d
  \citep[epoch defined in][]{tu00} and both show a spectral evolution in the [O~{\sc i}] lines regions different to
  that of PTF11kx. %The comparison also highlights that 
  \ca\/ and SN 1997cy have similar He~{\sc i} emission lines 
  (EW$_{{\rm 12ca}}^{\lambda5876}=$ EW$_{{\rm 97cy}}^{\lambda5876}\sim7$\AA\/, EW$_{{\rm 12ca}}^{\lambda7065}\sim16$\AA\/ and EW$_{{\rm 97cy}}^{\lambda7065}\sim18$\AA\/), and \Ha\/ FWHM velocity ($v_{\rm 12ca}\sim2900$ \kms\/ and $v_{\rm 97cy}\sim3200$ \kms\/). %while the \Ha\/ profile is
  %similar to that of SN~1997cy. 
  %\ca\/ shows an
  %increment of emission between 7000 \AA\/ and 8000 \AA\/ linked to Ca
  %and O lines, whereas PTF11kx does not {\bf and SN~1997cy is in between.}

%\begin{figure}
%\includegraphics[width=\columnwidth]{nir_cmp.eps}
%\caption{Comparison of the +170d NIR spectrum with that of the Type Ic SN 2007gr \citep[$\phi=+176$d;][]{hu09}. The spectra are corrected for Galactic reddening and reported at rest-frame.} 
%\label{fig:spcmp}
%\end{figure}

\section{Is \ca\/ an interacting CC-SNe?}\label{sec:dis}

The discovery of PTF11kx and its nature has changed the paradigm of
these SN1997cy-like events, leading \citet{si13b} to suggest a
thermonuclear origin for the majority, or even all, of these type of events. 
The data for SN2012ca indicate that it too is similar to SN1997cy and we consider it more likely to have a core-collapse origin.  The 
evidence for a core collapse interpretation are summarised as follows: 

\begin{itemize}

\item The overall spectral evolution of \ca\/ is hard to explain using
  diluted Type Ia spectra with superimposed emission. SNe Ia %evolve
 % rapidly in the first months and the nebular spectra (over one year)
 over one year
  are dominated by forbidden iron lines, as also shown by \citet{fi92}
  for the luminous SN1991T. On the contrary, a broad-line
  %energetic 
  Type Ic such as SN1998bw shows more spectral similarities.
  %a spectral evolution on a
  %longer time
  %scale. %However, even the long timescale of SN~1998bw is still not enough to explain \ca\/ line profiles at 375d.

\item O~{\sc i}, [O~{\sc i}] and [O~{\sc ii}] lines were likely
  identified, blue shifted by $\sim$2500 \kms\/.  A number of magnesium lines were
  identified, including Mg~{\sc i} $\lambda$15024 which is usually
  seen in spectra of Type Ic SNe %\citep[e.g. SNe 1998bw, 1999ex and
  %2004aw;][]{pa01,ha02,ta06}
  \citep[e.g. SNe 1998bw,
  2004aw;][]{pa01,ta06}. Both elements, and their observed line strengths are more
indicative of a massive progenitor and  CC-SN origin. 

 %No typical elements like S (e.g. S~{\sc ii} $\lambda$5468 and
  %S~{\sc i} $\lambda$10821), which are usually visible in Type Ia SNe
  %were detected, whereas 
\item  We detect [C~{\sc i}] at 8700 \AA\/ at 413 d
  with $v_{\rm FWHM}\gtrsim 1500$~\kms\/. This is again similar to
  what is typically seen in the ejecta of Type Ic SNe
  \citep[e.g.][]{fi97}.

\item The Ca~{\sc ii} NIR triplet is usually seen during the
  photospheric phase of Type Ia SNe \citep{fi97}. %Although weaker, it is typically still visible
  %after $\sim$5-6 months \citep[][]{fi92}. 
  Forbidden [Ca~{\sc ii}] 
  has been seen only in sub luminous SNe Ia \citep{fi92a}, but not in normal or bright (e.g. SN 1991T) SNe Ia.
% is generally missing in normal Type Ia, such as  the well sampled SN~2011fe
  %\citep{sh13}, although it was weakly detected 
  %in the peculiar, subluminous Type Ia PTF09dav
  %\citep{su11}. 
 % or in the interacting Type Ia SN 2006X \citep{pa07,wa08}.
  The SNe Ia ejecta environment is typically more strongly ionised
  than in SNe Ic, thus the absence of [Ca~{\sc ii}] in Type Ia SNe is
  probably linked to the fact that it is at a higher ionisation state \citep{li97,ma10}.
  Any possible interaction should enhance this effect, and so the
  presence of [Ca~{\sc ii}] in \ca\/ again points towards core
  collapse.

\item \Ha\/ narrow P-Cygni absorption from a wind has been detected
  with an expansion velocity of $\sim$200 \kms, a factor $\sim3$
  greater than what was seen in PTF11kx.

\item Broader and persistent He~{\sc i} emission lines have been detected in \ca\/, in contrast to what seen in PTF11kx.
Furthermore, it appears that little to no He~{\sc i} emission is a key attribute of members of the SN Ia-CSM class \citep{si13b}.
%Furthermore, from the analysis of \citet{si13b} on a large sample of SN1997cy-like appears that little to no He~{\sc i} emission is a key attribute of members of the SN Ia-CSM class. %It could be also difficult explain an H and He rich CSM coming from a possible AGB companion

%While the possible Si~{\sc ii} $\lambda$6355 absorption line identified in the complex profile close to \Ha\/ is often detected in both the types and does not provide an important discriminant.

\end{itemize}

\begin{figure}
\includegraphics[width=\columnwidth,height=6.9cm]{sp_cmp4new.eps}
\caption{Top: comparison of two spectra of \ca\/ with those of SNe 1991T \citep[Ia,][]{gl98} and 1998bw \citep[Ic,][]{pa01}. Bottom: comparison of the  two spectra of \ca\/ with those of PTF11kx \citep[][]{di12} and SN1997cy \citep[][]{tu00}. Balmer, He~{\sc i}, O~{\sc i} and [O~{\sc i}] features are indicated by vertical black, cyan and green dashed lines, respectively. %The spectra are corrected for Galactic reddening and reported at rest-frame. 
Phases with respect to maximum light.} 
\label{fig:spcmp}
\end{figure}

%The spectral analysis implies that the ejecta is H- and He-free, i.e.\ca\/ is a Type Ic SN. 
%The amount of He should be lesser than that seen in Type Ibn SNe as highlighted by the comparison with SN~2006jc, suggesting a stripped envelope SN with less He than a Type Ib, i.e. a Type Ic. 
%The resemblance with Type Ic SNe is strengthened by the spectra similarities with SN~1998bw.

The data favour the interpretation of \ca\/ as a CC-SN, %likely a Type Ic SN 
with a certain degree of asymmetry in the ejecta and surrounded by a H- and He-rich CSM. The interacting SN Ia scenario 
appears to work well for for PTF11kx but the link has been extended broadly to many SNe showing interaction
which are SN1997cy-like. We argue that this is almost certainly premature, and that the extensive data
set for SN2012ca, including the bolometric lightcurve and optical to NIR spectral sequence 
is strongly suggestive of a core-collapse origin. 
%is disfavoured for \ca\/ by our analysis.
%This suggests that  for a better understanding of these rare transients, nebular phases ($>$150d) are crucial and more important than photospherics.
%To account for both H and He emission from the CSM, the SN could perhaps arise from
%a binary system in which the companion loses H, while the SN progenitor loses its He envelope before exploding as a C-O core. 
The similarity to bright SNe Ic nebular spectra at phases of $>$150d
suggests that it could well have been a stripped envelope progenitor
which impacts and interacts with an H-rich CSM. %We argue that the strong
%[Fe II] lines inherent in 
%thermonuclear explosions are
%not observed and are incompatible with the SN~2012ca data. 
Although the 
presence of H in the spectra and narrow emission lines  suggest a 
classification as a Type IIn SN by definition, we do not find clear evidence that the SN 
ejecta was H-rich.  %\ca\/ shows only two components instead of the usual
%three in the Type IIn SNe which are likely caused by H-rich ejecta impacting H-rich 
%shells. 
This illustrates the limitations of our currently employed SN classification
nomenclature. Indeed SN2012ca and probably SN1997cy are better referred to as 
interacting stripped envelope SNe. %, in a similar analogy to the Ibn category used by \cite{2008MNRAS.389..113P}. 
%and the similarities with SNe Ic spectra are
%remarkable, thus we could encourage to refer to this object, as well
%as SN~1997cy and other objects resembling this (e.g. SNe 1999E and
%2002ic), as SNe~Icn.
%Despite the presence of H and He in the spectra and narrow emission lines, we disfavour the classification as a peculiar Type IIn because of the absence of an emission component related to the ejecta (\ca\/ shows only 2 components instead of the usual 3 in the Type IIn) and the spectral similarity to the stripped envelope SNe. Also taking in account the overall differences in light curve and spectral evolution between \ca\/ and the interacting stripped envelope SNe Ibn,
%Following the overall spectral resemblance with the Type Ic SNe and the simultaneous presence of narrow and broader H and He emission lines
%unrelated to the fast-moving ejecta, 
%we propose \ca\/ as SN Icn. This definition leads to a new subclass of stripped envelope SNe that
%can identify all the objects similar to \ca\/, e.g. SNe~1997cy, 1999E, 2002ic.
% current SN taxonomy propose it as a SN Icn.
% because shows H in spectra, also with narrow component, but they resemble a Type Ic. 
\ca\/ provides evidence of a viable alternative scenario to the
thermonuclear interpretation \citep[Ia-CSM,][]{si13b} about interacting SNe with H and He rich
CSM, suggesting that two different channels may be responsible for SN1997cy-like events.

\section*{Acknowledgments}
%CI thanks S. Sim for helpful discussions.
Based on observations collected by PESSTO, 
and the Panchromatic Robotic Optical Monitoring and Polarimetry
Telescope (PROMPT), Chile; 
the Australian National
University 2.3m Telescope and the Swift Satellite.
Funded by the European Research
Council under the European Union's Seventh Framework Programme
(FP7/2007-2013)/ERC Grant agreement n$^{\rm o}$ [291222] (SJS). SB and AP  acknowledge the PRIN-INAF 2011 project ``Transient Universe: from ESO Large to PESSTO". 
G.P.  acknowledges  Millennium Center for Supernova Science (P10-064-F).
%This research has made use of the NASA/IPAC Extragalactic
%Database (NED) which is operated by the Jet Propulsion Laboratory,
%California Institute of Technology, under contract with the National
%Aeronautics and Space Administration.


\begin{thebibliography}{99}
\bibitem[\protect\citeauthoryear{Aldering et 
al.}{2006}]{al06} Aldering G., et al., 2006, ApJ, 650, 510
\bibitem[\protect\citeauthoryear{Benetti et 
al.}{2006}]{be06} Benetti S., Cappellaro E., Turatto M., 
Taubenberger S., Harutyunyan A., Valenti S., 2006, ApJ, 653, L129 
%\bibitem[\protect\citeauthoryear{Cappellaro et 
%al.}{1997}]{ca97} Cappellaro E., Mazzali P.~A., Benetti S., Danziger I.~J., Turatto M., della Valle M., Patat F., 1997, A\&A, 328, 203
\bibitem[\protect\citeauthoryear{Chevalier 
\& Fransson}{1994}]{cf94} Chevalier R.~A., Fransson C., 1994, ApJ, 420, 268
%\bibitem[\protect\citeauthoryear{Chugai, Chevalier, 
%\& Lundqvist}{2004}]{ch04} Chugai N.~N., Chevalier R.~A., Lundqvist P., 2004, MNRAS, 355, 627 
\bibitem[\protect\citeauthoryear{Chugai}{2001}]{ch01} Chugai 
N.~N., 2001, MNRAS, 326, 1448
%\bibitem[\protect\citeauthoryear{Clocchiatti et 
%al.}{1996}]{cl96} Clocchiatti A., Wheeler J.~C., Brotherton 
%M.~S., Cochran A.~L., Wills D., Barker E.~S., Turatto M., 1996, ApJ, 462, 
%462 
\bibitem[\protect\citeauthoryear{Deng et al.}{2004}]{de04} 
Deng J., et al., 2004, ApJ, 605, L37 
\bibitem[\protect\citeauthoryear{Dessart et 
al.}{2009}]{de09} Dessart L., Hillier D.~J., Gezari S., Basa 
S., Matheson T., 2009, MNRAS, 394, 21 
\bibitem[\protect\citeauthoryear{Dilday et al.}{2012}]{di12} 
Dilday B., et al., 2012, Sci, 337, 942
\bibitem[\protect\citeauthoryear{Drescher, Parker, 
\& Brimacombe}{2012}]{dr12} Drescher C., Parker S., Brimacombe J., 2012,  CBET,3101,1
%\bibitem[\protect\citeauthoryear{Fox et al.}{2011}]{fo11} 
%Fox O.~D., et al., 2011, ApJ, 741, 7 
\bibitem[\protect\citeauthoryear{Filippenko}{1997}]{fi97} Filippenko A.~V., 1997, ARA\&A, 35, 309 
\bibitem[\protect\citeauthoryear{Filippenko et 
al.}{1992}]{fi92a} Filippenko A.~V., et al., 1992, AJ, 104, 
1543
\bibitem[\protect\citeauthoryear{Filippenko et 
al.}{1992}]{fi92} Filippenko A.~V., et al., 1992, ApJ, 384, 
L15
\bibitem[\protect\citeauthoryear{Fraser et al.}{2013}]{fr13} 
Fraser M., et al., 2013, MNRAS, 1499
\bibitem[\protect\citeauthoryear{Galama et al.}{1998}]{ga98} 
Galama T.~J., et al., 1998, Natur, 395, 670
%\bibitem[\protect\citeauthoryear{Garavini et 
%al.}{2004}]{ge04} Garavini G., et al., 2004, AJ, 128, 387 
\bibitem[\protect\citeauthoryear{Germany et 
al.}{2000}]{ge00} Germany L.~M., Reiss D.~J., Sadler E.~M., 
Schmidt B.~P., Stubbs C.~W., 2000, ApJ, 533, 320
\bibitem[\protect\citeauthoryear{G{\'o}mez 
\& L{\'o}pez}{1998}]{gl98} G{\'o}mez G., L{\'o}pez R., 1998, AJ, 115, 1096
\bibitem[\protect\citeauthoryear{Hamuy et al.}{2003}]{ha03} 
Hamuy M., et al., 2003, Natur, 424, 651
\bibitem[\protect\citeauthoryear{Hamuy et al.}{2002}]{ha02} 
Hamuy M., et al., 2002, AJ, 124, 417
\bibitem[\protect\citeauthoryear{Heger et al.}{2003}]{he03} 
Heger A., Fryer C.~L., Woosley S.~E., Langer N., Hartmann D.~H., 2003, ApJ, 
591, 288 
\bibitem[\protect\citeauthoryear{Hillebrandt \& Niemeyer}{2000}]{hn00} Hillebrandt W., Niemeyer J.~C., 2000, ARA\&A, 38, 191
\bibitem[\protect\citeauthoryear{Hunter et 
al.}{2009}]{hu09} Hunter D.~J., et al., 2009, A\&A, 508, 371
%\bibitem[\protect\citeauthoryear{Inserra et 
%al.}{2013}]{in13b} Inserra C., et al., 2013, A\&A, 555, A142
\bibitem[\protect\citeauthoryear{Inserra et 
al.}{2013}]{in13} Inserra C., et al., 2013, ApJ, 770, 128
\bibitem[\protect\citeauthoryear{Inserra et 
al.}{2012}]{in12} Inserra C., et al., 2012, CBET, 3101, 1
\bibitem[Janka(2012)]{2012ARNPS..62..407J} Janka, H.-T.\ 2012, Annu. Rev. Nucl. Part. Sci., 62, 407 
%\bibitem[\protect\citeauthoryear{Kotak et al.}{2004}]{ko04} 
%Kotak R., Meikle W.~P.~S., Adamson A., Leggett S.~K., 2004, MNRAS, 354, L13 
\bibitem[Langer(2012)]{2012ARA&A..50..107L} Langer, N.\ 2012, ARA\&A, 50, 107 
\bibitem[\protect\citeauthoryear{Lira et al.}{1998}]{li98} 
Lira P., et al., 1998, AJ, 115, 234
\bibitem[\protect\citeauthoryear{Liu, Jeffery, 
\& Schultz}{1997}]{li97} Liu W., Jeffery D.~J., Schultz D.~R., 1997, ApJ, 483, L107
%\bibitem[\protect\citeauthoryear{Matheson et 
%al.}{2008}]{ma08} Matheson T., et al., 2008, AJ, 135, 1598
%\bibitem[\protect\citeauthoryear{Pastorello et 
%al.}{2008}]{pas08} Pastorello A., et al., 2008, MNRAS, 389, 
%113
%\bibitem[\protect\citeauthoryear{Maurer et al.}{2011}]{ma11} 
%Maurer I., Jerkstrand A., Mazzali P.~A., Taubenberger S., Hachinger S., 
%Kromer M., Sim S., Hillebrandt W., 2011, MNRAS, 418, 1517
\bibitem[\protect\citeauthoryear{Mazzali et 
al.}{2010}]{ma10} Mazzali P.~A., Maurer I., Valenti S., 
Kotak R., Hunter D., 2010, MNRAS, 408, 87 
\bibitem[\protect\citeauthoryear{Pastorello et 
al.}{2007}]{pas07} Pastorello A., et al., 2007, Natur, 447, 
829
%\bibitem[Pastorello et al.(2008)]{2008MNRAS.389..113P} Pastorello, A., 
%Mattila, S., Zampieri, L., et al.\ 2008, MNRAS, 389, 113 
\bibitem[\protect\citeauthoryear{Patat et 
al.}{2011}]{pa11} Patat F., Chugai N.~N., Podsiadlowski P., Mason E., Melo C., Pasquini L., 2011, A\&A, 530, A63 
%\bibitem[\protect\citeauthoryear{Patat et al.}{2007}]{pa07} 
%Patat F., et al., 2007, Sci, 317, 924
\bibitem[\protect\citeauthoryear{Patat et al.}{2001}]{pa01} 
Patat F., et al., 2001, ApJ, 555, 900
\bibitem[\protect\citeauthoryear{Prieto et al.}{2007}]{pr07} 
Prieto J.~L., et al., 2007, arXiv, arXiv:0706.4088
\bibitem[\protect\citeauthoryear{Reichart et 
al.}{2005}]{re05} Reichart D., et al., 2005, NCimC, 28, 767
%\bibitem[\protect\citeauthoryear{Richmond et 
%al.}{1996}]{ri96} Richmond M.~W., et al., 1996, AJ, 111, 327
%\bibitem[\protect\citeauthoryear{Rigon et al.}{2003}]{ri03} 
%Rigon L., et al., 2003, MNRAS, 340, 191 
\bibitem[\protect\citeauthoryear{Schlafly 
\& Finkbeiner}{2011}]{sf11} Schlafly E.~F., Finkbeiner D.~P., 2011, ApJ, 737, 103
%\bibitem[\protect\citeauthoryear{Shappee et 
%al.}{2013}]{sh13} Shappee B.~J., Stanek K.~Z., Pogge R.~W., 
%Garnavich P.~M., 2013, ApJ, 762, L5
\bibitem[\protect\citeauthoryear{Silverman et 
al.}{2013a}]{si13a} Silverman J.~M., et al., 2013a, ApJ, 772, 
125 
\bibitem[\protect\citeauthoryear{Silverman et 
al.}{2013b}]{si13b} Silverman J.~M., et al., 2013b, ApJS, 207, 
3
%\bibitem[\protect\citeauthoryear{Silverman et 
%al.}{2012}]{si12} Silverman J.~M., et al., 2012, MNRAS, 425, 
%1789
\bibitem[Smartt(2009)]{2009ARA&A..47...63S} Smartt, S.~J.\ 2009, ARA\&A, 47, 63 
\bibitem[\protect\citeauthoryear{Smith et al.}{2009}]{sm09} 
Smith N., et al., 2009, ApJ, 695, 1334
\bibitem[\protect\citeauthoryear{Sternberg et 
al.}{2011}]{st11} Sternberg A., et al., 2011, Sci, 333, 856
%\bibitem[\protect\citeauthoryear{Sullivan et 
%al.}{2011}]{su11} Sullivan M., et al., 2011, ApJ, 732, 118
\bibitem[\protect\citeauthoryear{Taddia et 
al.}{2012}]{ta12} Taddia F., et al., 2012, A\&A, 545, L7
\bibitem[\protect\citeauthoryear{Taubenberger et 
al.}{2006}]{ta06} Taubenberger S., et al., 2006, MNRAS, 371, 
1459
\bibitem[\protect\citeauthoryear{Trundle et 
al.}{2008}]{tr08} Trundle C., Kotak R., Vink J.~S., Meikle W.~P.~S., 2008, A\&A, 483, L47
%\bibitem[\protect\citeauthoryear{Turatto}{2003}]{tu03} 
%Turatto M., 2003, LNP, 598, 21 
\bibitem[\protect\citeauthoryear{Turatto et 
al.}{2000}]{tu00} Turatto M., et al., 2000, ApJ, 534, L57
%\bibitem[\protect\citeauthoryear{Turatto et 
%al.}{1993}]{tu93} Turatto M., Cappellaro E., Danziger I.~J., 
%Benetti S., Gouiffes C., della Valle M., 1993, MNRAS, 262, 128 
\bibitem[\protect\citeauthoryear{Valenti et 
al.}{2013}]{va13} Valenti S., et al., 2013, arXiv, 
arXiv:1302.2983
\bibitem[\protect\citeauthoryear{Valenti et 
al.}{2012}]{va12} Valenti S., et al., 2012, ATel, 4076, 1
%\bibitem[\protect\citeauthoryear{Valenti et 
%al.}{2008}]{va08} Valenti S., et al., 2008, ApJ, 673, L155 
%\bibitem[\protect\citeauthoryear{Wang et al.}{2008}]{wa08} 
%Wang X., et al., 2008, ApJ, 675, 626
\bibitem[\protect\citeauthoryear{Wood-Vasey, Wang, 
\& Aldering}{2004}]{wv04} Wood-Vasey W.~M., Wang L., Aldering G., 2004, ApJ, 616, 339
\bibitem[\protect\citeauthoryear{Yaron 
\& Gal-Yam}{2012}]{ya12} Yaron O., Gal-Yam A., 2012, PASP, 124, 668 
\bibitem[\protect\citeauthoryear{Zhang et al.}{2012}]{zh12} 
Zhang T., et al., 2012, AJ, 144, 131 
\end{thebibliography}


\end{document}

1307.1791.extracted_bib
\begin{thebibliography}{99}
\bibitem[\protect\citeauthoryear{Aldering et 
al.}{2006}]{al06} Aldering G., et al., 2006, ApJ, 650, 510
\bibitem[\protect\citeauthoryear{Benetti et 
al.}{2006}]{be06} Benetti S., Cappellaro E., Turatto M., 
Taubenberger S., Harutyunyan A., Valenti S., 2006, ApJ, 653, L129 
%\bibitem[\protect\citeauthoryear{Cappellaro et 
%al.}{1997}]{ca97} Cappellaro E., Mazzali P.~A., Benetti S., Danziger I.~J., Turatto M., della Valle M., Patat F., 1997, A\&A, 328, 203
\bibitem[\protect\citeauthoryear{Chevalier 
\& Fransson}{1994}]{cf94} Chevalier R.~A., Fransson C., 1994, ApJ, 420, 268
%\bibitem[\protect\citeauthoryear{Chugai, Chevalier, 
%\& Lundqvist}{2004}]{ch04} Chugai N.~N., Chevalier R.~A., Lundqvist P., 2004, MNRAS, 355, 627 
\bibitem[\protect\citeauthoryear{Chugai}{2001}]{ch01} Chugai 
N.~N., 2001, MNRAS, 326, 1448
%\bibitem[\protect\citeauthoryear{Clocchiatti et 
%al.}{1996}]{cl96} Clocchiatti A., Wheeler J.~C., Brotherton 
%M.~S., Cochran A.~L., Wills D., Barker E.~S., Turatto M., 1996, ApJ, 462, 
%462 
\bibitem[\protect\citeauthoryear{Deng et al.}{2004}]{de04} 
Deng J., et al., 2004, ApJ, 605, L37 
\bibitem[\protect\citeauthoryear{Dessart et 
al.}{2009}]{de09} Dessart L., Hillier D.~J., Gezari S., Basa 
S., Matheson T., 2009, MNRAS, 394, 21 
\bibitem[\protect\citeauthoryear{Dilday et al.}{2012}]{di12} 
Dilday B., et al., 2012, Sci, 337, 942
\bibitem[\protect\citeauthoryear{Drescher, Parker, 
\& Brimacombe}{2012}]{dr12} Drescher C., Parker S., Brimacombe J., 2012,  CBET,3101,1
%\bibitem[\protect\citeauthoryear{Fox et al.}{2011}]{fo11} 
%Fox O.~D., et al., 2011, ApJ, 741, 7 
\bibitem[\protect\citeauthoryear{Filippenko}{1997}]{fi97} Filippenko A.~V., 1997, ARA\&A, 35, 309 
\bibitem[\protect\citeauthoryear{Filippenko et 
al.}{1992}]{fi92a} Filippenko A.~V., et al., 1992, AJ, 104, 
1543
\bibitem[\protect\citeauthoryear{Filippenko et 
al.}{1992}]{fi92} Filippenko A.~V., et al., 1992, ApJ, 384, 
L15
\bibitem[\protect\citeauthoryear{Fraser et al.}{2013}]{fr13} 
Fraser M., et al., 2013, MNRAS, 1499
\bibitem[\protect\citeauthoryear{Galama et al.}{1998}]{ga98} 
Galama T.~J., et al., 1998, Natur, 395, 670
%\bibitem[\protect\citeauthoryear{Garavini et 
%al.}{2004}]{ge04} Garavini G., et al., 2004, AJ, 128, 387 
\bibitem[\protect\citeauthoryear{Germany et 
al.}{2000}]{ge00} Germany L.~M., Reiss D.~J., Sadler E.~M., 
Schmidt B.~P., Stubbs C.~W., 2000, ApJ, 533, 320
\bibitem[\protect\citeauthoryear{G{\'o}mez 
\& L{\'o}pez}{1998}]{gl98} G{\'o}mez G., L{\'o}pez R., 1998, AJ, 115, 1096
\bibitem[\protect\citeauthoryear{Hamuy et al.}{2003}]{ha03} 
Hamuy M., et al., 2003, Natur, 424, 651
\bibitem[\protect\citeauthoryear{Hamuy et al.}{2002}]{ha02} 
Hamuy M., et al., 2002, AJ, 124, 417
\bibitem[\protect\citeauthoryear{Heger et al.}{2003}]{he03} 
Heger A., Fryer C.~L., Woosley S.~E., Langer N., Hartmann D.~H., 2003, ApJ, 
591, 288 
\bibitem[\protect\citeauthoryear{Hillebrandt \& Niemeyer}{2000}]{hn00} Hillebrandt W., Niemeyer J.~C., 2000, ARA\&A, 38, 191
\bibitem[\protect\citeauthoryear{Hunter et 
al.}{2009}]{hu09} Hunter D.~J., et al., 2009, A\&A, 508, 371
%\bibitem[\protect\citeauthoryear{Inserra et 
%al.}{2013}]{in13b} Inserra C., et al., 2013, A\&A, 555, A142
\bibitem[\protect\citeauthoryear{Inserra et 
al.}{2013}]{in13} Inserra C., et al., 2013, ApJ, 770, 128
\bibitem[\protect\citeauthoryear{Inserra et 
al.}{2012}]{in12} Inserra C., et al., 2012, CBET, 3101, 1
\bibitem[Janka(2012)]{2012ARNPS..62..407J} Janka, H.-T.\ 2012, Annu. Rev. Nucl. Part. Sci., 62, 407 
%\bibitem[\protect\citeauthoryear{Kotak et al.}{2004}]{ko04} 
%Kotak R., Meikle W.~P.~S., Adamson A., Leggett S.~K., 2004, MNRAS, 354, L13 
\bibitem[Langer(2012)]{2012ARA&A..50..107L} Langer, N.\ 2012, ARA\&A, 50, 107 
\bibitem[\protect\citeauthoryear{Lira et al.}{1998}]{li98} 
Lira P., et al., 1998, AJ, 115, 234
\bibitem[\protect\citeauthoryear{Liu, Jeffery, 
\& Schultz}{1997}]{li97} Liu W., Jeffery D.~J., Schultz D.~R., 1997, ApJ, 483, L107
%\bibitem[\protect\citeauthoryear{Matheson et 
%al.}{2008}]{ma08} Matheson T., et al., 2008, AJ, 135, 1598
%\bibitem[\protect\citeauthoryear{Pastorello et 
%al.}{2008}]{pas08} Pastorello A., et al., 2008, MNRAS, 389, 
%113
%\bibitem[\protect\citeauthoryear{Maurer et al.}{2011}]{ma11} 
%Maurer I., Jerkstrand A., Mazzali P.~A., Taubenberger S., Hachinger S., 
%Kromer M., Sim S., Hillebrandt W., 2011, MNRAS, 418, 1517
\bibitem[\protect\citeauthoryear{Mazzali et 
al.}{2010}]{ma10} Mazzali P.~A., Maurer I., Valenti S., 
Kotak R., Hunter D., 2010, MNRAS, 408, 87 
\bibitem[\protect\citeauthoryear{Pastorello et 
al.}{2007}]{pas07} Pastorello A., et al., 2007, Natur, 447, 
829
%\bibitem[Pastorello et al.(2008)]{2008MNRAS.389..113P} Pastorello, A., 
%Mattila, S., Zampieri, L., et al.\ 2008, MNRAS, 389, 113 
\bibitem[\protect\citeauthoryear{Patat et 
al.}{2011}]{pa11} Patat F., Chugai N.~N., Podsiadlowski P., Mason E., Melo C., Pasquini L., 2011, A\&A, 530, A63 
%\bibitem[\protect\citeauthoryear{Patat et al.}{2007}]{pa07} 
%Patat F., et al., 2007, Sci, 317, 924
\bibitem[\protect\citeauthoryear{Patat et al.}{2001}]{pa01} 
Patat F., et al., 2001, ApJ, 555, 900
\bibitem[\protect\citeauthoryear{Prieto et al.}{2007}]{pr07} 
Prieto J.~L., et al., 2007, arXiv, arXiv:0706.4088
\bibitem[\protect\citeauthoryear{Reichart et 
al.}{2005}]{re05} Reichart D., et al., 2005, NCimC, 28, 767
%\bibitem[\protect\citeauthoryear{Richmond et 
%al.}{1996}]{ri96} Richmond M.~W., et al., 1996, AJ, 111, 327
%\bibitem[\protect\citeauthoryear{Rigon et al.}{2003}]{ri03} 
%Rigon L., et al., 2003, MNRAS, 340, 191 
\bibitem[\protect\citeauthoryear{Schlafly 
\& Finkbeiner}{2011}]{sf11} Schlafly E.~F., Finkbeiner D.~P., 2011, ApJ, 737, 103
%\bibitem[\protect\citeauthoryear{Shappee et 
%al.}{2013}]{sh13} Shappee B.~J., Stanek K.~Z., Pogge R.~W., 
%Garnavich P.~M., 2013, ApJ, 762, L5
\bibitem[\protect\citeauthoryear{Silverman et 
al.}{2013a}]{si13a} Silverman J.~M., et al., 2013a, ApJ, 772, 
125 
\bibitem[\protect\citeauthoryear{Silverman et 
al.}{2013b}]{si13b} Silverman J.~M., et al., 2013b, ApJS, 207, 
3
%\bibitem[\protect\citeauthoryear{Silverman et 
%al.}{2012}]{si12} Silverman J.~M., et al., 2012, MNRAS, 425, 
%1789
\bibitem[Smartt(2009)]{2009ARA&A..47...63S} Smartt, S.~J.\ 2009, ARA\&A, 47, 63 
\bibitem[\protect\citeauthoryear{Smith et al.}{2009}]{sm09} 
Smith N., et al., 2009, ApJ, 695, 1334
\bibitem[\protect\citeauthoryear{Sternberg et 
al.}{2011}]{st11} Sternberg A., et al., 2011, Sci, 333, 856
%\bibitem[\protect\citeauthoryear{Sullivan et 
%al.}{2011}]{su11} Sullivan M., et al., 2011, ApJ, 732, 118
\bibitem[\protect\citeauthoryear{Taddia et 
al.}{2012}]{ta12} Taddia F., et al., 2012, A\&A, 545, L7
\bibitem[\protect\citeauthoryear{Taubenberger et 
al.}{2006}]{ta06} Taubenberger S., et al., 2006, MNRAS, 371, 
1459
\bibitem[\protect\citeauthoryear{Trundle et 
al.}{2008}]{tr08} Trundle C., Kotak R., Vink J.~S., Meikle W.~P.~S., 2008, A\&A, 483, L47
%\bibitem[\protect\citeauthoryear{Turatto}{2003}]{tu03} 
%Turatto M., 2003, LNP, 598, 21 
\bibitem[\protect\citeauthoryear{Turatto et 
al.}{2000}]{tu00} Turatto M., et al., 2000, ApJ, 534, L57
%\bibitem[\protect\citeauthoryear{Turatto et 
%al.}{1993}]{tu93} Turatto M., Cappellaro E., Danziger I.~J., 
%Benetti S., Gouiffes C., della Valle M., 1993, MNRAS, 262, 128 
\bibitem[\protect\citeauthoryear{Valenti et 
al.}{2013}]{va13} Valenti S., et al., 2013, arXiv, 
arXiv:1302.2983
\bibitem[\protect\citeauthoryear{Valenti et 
al.}{2012}]{va12} Valenti S., et al., 2012, ATel, 4076, 1
%\bibitem[\protect\citeauthoryear{Valenti et 
%al.}{2008}]{va08} Valenti S., et al., 2008, ApJ, 673, L155 
%\bibitem[\protect\citeauthoryear{Wang et al.}{2008}]{wa08} 
%Wang X., et al., 2008, ApJ, 675, 626
\bibitem[\protect\citeauthoryear{Wood-Vasey, Wang, 
\& Aldering}{2004}]{wv04} Wood-Vasey W.~M., Wang L., Aldering G., 2004, ApJ, 616, 339
\bibitem[\protect\citeauthoryear{Yaron 
\& Gal-Yam}{2012}]{ya12} Yaron O., Gal-Yam A., 2012, PASP, 124, 668 
\bibitem[\protect\citeauthoryear{Zhang et al.}{2012}]{zh12} 
Zhang T., et al., 2012, AJ, 144, 131 
\end{thebibliography}