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Inserra, C. and Smartt, S.J. and Jerkstrand, A. and Valenti, S. and Fraser, M. and Wright, D. and Smith, K.
and Chen, T.-W. and Kotak, R. and Pastorello, A. and Nicholl, M. and Bresolin, F. and Kudritzki, R.P. and
Benetti, S. and Botticella, M.T. and Burgett, W.S. and Chambers, K.C. and Ergon, M. and Flewelling, H. and
Fynbo, J.P.U. and Geier, S. and Hodapp, K.W. and Howell, D.A. and Huber, M. and Kaiser, N. and Leloudas,
G. and Magill, L. and Magnier, E.A. and McCrum, M.G. and Metcalfe, N. and Price, P.A. and Rest, A. and
Sollerman, J. and Sweeney, W. and Taddia, F. and Taubenberger, S. and Tonry, J.L. and Wainscoat, R.J. and
Waters, C. and Young, D. (2013) 'Super-luminous type Ic supernovae : catching a magnetar by the tail.',
Astrophysical journal., 770 (2). p. 128.
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http://dx.doi.org/10.1088/0004-637X/770/2/128
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The Astrophysical Journal, 770:128 (28pp), 2013 June 20 doi:10.1088/0004-637X/770/2/128
C
2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
SUPER-LUMINOUS TYPE Ic SUPERNOVAE: CATCHING A MAGNETAR BY THE TAIL
C. Inserra
1
, S. J. Smartt
1
, A. Jerkstrand
1
, S. Valenti
2,3
, M. Fraser
1
, D. Wright
1
,K.Smith
1
, T.-W. Chen
1
, R. Kotak
1
,
A. Pastorello
4
, M. Nicholl
1
, F. Bresolin
5
, R. P. Kudritzki
5
, S. Benetti
4
, M. T. Botticella
6
, W. S. Burgett
5
,
K. C. Chambers
5
, M. Ergon
7
, H. Flewelling
5
, J. P. U. Fynbo
8
, S. Geier
8,9
, K. W. Hodapp
5
, D. A. Howell
2,3
, M. Huber
5
,
N. Kaiser
5
, G. Leloudas
8,10
, L. Magill
1
,E.A.Magnier
5
,M.G.McCrum
1
, N. Metcalfe
11
, P. A. Price
5
,A.Rest
12
,
J. Sollerman
7
, W. Sweeney
5
, F. Taddia
7
, S. Taubenberger
13
,J.L.Tonry
5
, R. J. Wainscoat
5
, C. Waters
5
, and D. Young
1
1
Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN, UK; c.inserra@qub.ac.uk
2
Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102 Goleta, CA 93117, USA
3
Department of Physics, University of California, Santa Barbara, Broida Hall, Mail Code 9530, Santa Barbara, CA 93106-9530, USA
4
INAF, Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, I-35122 Padova, Italy
5
Institute of Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
6
INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli, Italy
7
The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-10691 Stockholm, Sweden
8
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
9
Nordic Optical Telescope, Apartado 474, E-38700 Santa Cruz de La Palma, Spain
10
The Oskar Klein Centre, Department of Physics, Stockholm University, SE-10691 Stockholm, Sweden
11
Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
12
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
13
Max-Planck-Institut f
¨
ur Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany
Received 2013 April 11; accepted 2013 April 30; published 2013 June 4
ABSTRACT
We report extensive observational data for five of the lowest redshift Super-Luminous Type Ic Supernovae
(SL-SNe Ic) discovered to date, namely, PTF10hgi, SN2011ke, PTF11rks, SN2011kf, and SN2012il. Photometric
imaging of the transients at +50 to +230 days after peak combined with host galaxy subtraction reveals a luminous
tail phase for four of these SL-SNe. A high-resolution, optical, and near-infrared spectrum from xshooter provides
detection of a broad He i λ10830 emission line in the spectrum (+50 days) of SN2012il, revealing that at least
some SL-SNe Ic are not completely helium-free. At first sight, the tail luminosity decline rates that we measure are
consistent with the radioactive decay of
56
Co, and would require 1–4 M
of
56
Ni to produce the luminosity. These
56
Ni masses cannot be made consistent with the short diffusion times at peak, and indeed are insufficient to power the
peak luminosity. We instead favor energy deposition by newborn magnetars as the power source for these objects. A
semi-analytical diffusion model with energy input from the spin-down of a magnetar reproduces the extensive light
curve data well. The model predictions of ejecta velocities and temperatures which are required are in reasonable
agreement with those determined from our observations. We derive magnetar energies of 0.4 E(10
51
erg)
6.9 and ejecta masses of 2.3 M
ej
(M
) 8.6. The sample of five SL-SNe Ic presented here, combined with
SN 2010gx—the best sampled SL-SNe Ic so far—points toward an explosion driven by a magnetar as a viable
explanation for all SL-SNe Ic.
Key words: stars: magnetars – supernovae: general – supernovae: individual (PTF10hgi, PTF11rks, SN 2011ke,
SN 2011kf, SN 2012il)
Online-only material: color figures
1. INTRODUCTION
The discovery of unusually luminous optical transients by
modern supernova (SN) surveys has dramatically expanded the
observational and physical parameter space of known SN types.
The Texas Supernova Search was a pioneer in this area, with one
of the first searches of the local universe without a galaxy bias
(Quimby et al. 2005). This has been followed by deeper, wider
surveys from the Palomar Transient Factory (PTF; Rau et al.
2009), the Panoramic Survey Telescope and Rapid Response
System (Pan-STARRS; Kaiser et al. 2010), the Catalina Real-
time Transient Survey (CRTS; Drake et al. 2009), and the
La Silla QUEST survey (Hadjiyska et al. 2012), all of which
have found unusually luminous transients which tend to be
hosted in intrinsically faint galaxies. These Super-Luminous
SNe (SL-SNe) show absolute magnitudes at maximum light
of M
AB
< −21 mag and total radiated energies of the order
of 10
51
erg. They are factors of 5–100 brighter than Type Ia
SNe or normal core-collapse events. Gal-Yam (2012) proposed
that three distinct physical groups of SL-SNe have emerged. The
first group which was recognized was the luminous Type IIn
SNe epitomized by SN 2006gy (Smith et al. 2007; Smith &
McCray 2007;Ofeketal.2007; Agnoletto et al. 2009), which
show signs of strong circumstellar interaction. The second group
includes Type Ic SNe that have broad, bright light curves and
decay rates that imply that they could be due to pair-instability
explosions powered by large ejecta masses of
56
Ni (3–5 M
).
To date only one object of this type (SN 2007bi) has been
published and studied in detail (Gal-Yam et al. 2009; Young
et al. 2010). The third group was labeled by Gal-Yam (2012)
as Super-Luminous Type I SNe (SL-SNe I) and the two earliest
examples are SCP-06F6 and SN 2005ap (Barbary et al. 2009;
Quimby et al. 2007), which are characterized at early times
by a blue continuum and a distinctive “W”-shaped spectral
feature at ∼4200 Å. In this paper we will call this type Super-
Luminous Type Ic SNe (or SL-SNe Ic), simply because they are
Type Ic in the established SN nomenclature and are extremely
luminous.
The existence of this class of SL-SNe Ic was firmly estab-
lished when secure redshifts were determined with the identifi-
1
The Astrophysical Journal, 770:128 (28pp), 2013 June 20 Inserra et al.
cation of narrow Mg ii λλ2796, 2803 absorption from the host
galaxies in the optical spectra of z>0.2 transients by Quimby
et al. (2011b). The spectra of four PTF transients, SCP-06F6,
and SN 2005ap were then all linked together with these red-
shifts establishing a common type (Quimby et al. 2011b). Sub-
sequently, the identification of host galaxy emission lines such
as [O ii] λ3727, [O iii] λλ1959, 5007, Hα, and Hβ has con-
firmed the redshift derived from the Mg ii absorption in many
SL-SNe Ic, such as in the case of SN 2010gx (Quimby et al.
2010; Mahabal & Drake 2010; Pastorello et al. 2010). These
distances imply an incredible luminosity with u- and g-band ab-
solute magnitudes reaching about −22. This luminosity allowed
these SNe to be easily identified in the Pan-STARRS Medium
Deep fields at z ∼ 1 (Chomiuk et al. 2011) and beyond (Berger
et al. 2012).
The typical spectroscopic signature of the class of
SL-SNe Ic is a blue continuum with broad absorption lines
of intermediate-mass elements such as C, O, Si, Mg with ve-
locities 10,000 km s
−1
<v<20,000 km s
−1
. No clear ev-
idence of H or He has been found so far in the spectra of
SL-SNe Ic, whereas Fe, Mg, and Si lines are typically promi-
nent after maximum. The study of the well-sampled SN 2010gx
(Pastorello et al. 2010) showed an unexpected transformation
from an SL-SN Ic spectrum to that of a normal Type Ic SN.
A similar transformation was also observed in the late-time
spectrum of PTF09cnd (Quimby et al. 2011b), which evolved
to become consistent with a slowly evolving Type Ic SN.
The SL-SNe Ic discovered to date appear to be associated
with faint and metal-poor galaxies at redshifts ranging between
0.23 and 1.19 (typically M
g
> −17 mag; Quimby et al.
2011b; Neill et al. 2011; Chomiuk et al. 2011; Chen et al.
2013), although the highest redshift SL-SNe Ic (PS1-12bam,
z = 1.566) is in a galaxy which is more luminous and more
massive than the lower redshift counterparts (Berger et al.
2012). An estimate of the metallicity of the faint host galaxy
of SN 2010gx, from the detection of the auroral [O iii] λ4363
line, indicates a very low metallicity of 0.05 Z
(Chen et al.
2013). Research on SL-SNe Ic is progressing rapidly, with 13
of these intriguing transients now identified since the discovery
of SCP-06F6. To power the enormous peak luminosity of
SL-SNe Ic with radioactive decay would require several solar
masses of
56
Ni. However, this is inconsistent with the width of
the light curves as shown by Chomiuk et al. (2011). The light
curves cannot be reproduced with a physical model that has an
ejecta mass significantly greater than the
56
Ni mass needed to
power the peak. In the case of SN 2010gx, Chen et al. (2013)
showed that the tail phase faded to levels which would imply
an upper limit of around 0.4 M
of
56
Ni. Among the scenarios
proposed to explain the remarkable peak luminosity are the spin
down of a rapidly rotating young magnetar (Kasen & Bildsten
2010; Woosley 2010) that provides an additional reservoir of
energy for the SN (Ostriker & Gunn 1971;Usov1992; Wheeler
et al. 2000; Thompson et al. 2004); the interaction of the
SN ejecta with a massive (3–5 M
)C/O-rich circumstellar
medium (CSM; Blinnikov & Sorokina 2010) or with a dense
wind (Chevalier & Irwin 2011; Ginzburg & Balberg 2012); or
collisions between high-velocity shells ejected by a pulsational
pair instability, which would give rise to successive bright
optical transients (Woosley et al. 2007).OneoftheseSNe
(SN 2006oz) was discovered 29 days before peak luminosity
and showed a flat plateau in the rest-frame NUV before its rise
to maximum, indicating that finding these objects early could
give constraints on the explosion channel (Leloudas et al. 2012).
In most cases to date, however (apart from SN 2010gx; Chen
et al. 2013), the lightcurves and energy released at >100 d is
unexplored territory. Chen et al. (2013) quantified the host of
SN 2010gx, but difference imaging showed no detection of SN
flux at 250–300 days to deep limits. Quimby et al. (2011a)
detected flux at the position of PTF09cnd at +138 d after peak
in a B-band image, but it is not clear if this flux is from the
host or the SN. In this paper we present the detailed follow-up
of five SL-SNe Ic at 0.100 <z<0.245, namely, PTF11rks,
SN 2011ke, SN 2012il, PTF10hgi, and SN 2011kf, and attempt
to follow them for as long as possible to garner further evidence
to probe the physical mechanism powering these intriguing
events. A detailed analysis of their hosts will be part of a future
paper (T.-W. Chen et al., in preparation).
This paper is organized as follows. In Section 2 we introduce
the SNe, and report distances and reddening values. Photometric
data, light and color curves, as well as the absolute light curves
in the rest frame are presented in Section 3. Section 4 is
devoted to the analysis of bolometric and pseudo-bolometric
light curves and the evaluation of possible ejected
56
Ni masses,
while in Section 5 we describe and analyze the spectra. Finally,
a discussion about the origin of these transients is presented in
Section 6, followed by a short summary in Section 7.
2. DISCOVERY AND TARGET SAMPLE
2.1. Pan-STARRS1 Data: Discovery and Recovery
of the Transients
The strong tendency for these SL-SNe to be hosted in
faint galaxies appears not to be a bias, which suggests a
straightforward way of finding them in large volume, wide-
field searches. With the Pan-STARRS1 survey, we have been
running the “Faint Galaxy Supernova Survey” (FGSS) which is
aimed at finding transients in faint galaxies originally identified
in the Sloan Digital Sky Survey (SDSS) catalog (Valenti et al.
2010).
The Pan-STARRS1 optical system uses a 1.8 m diameter
aspheric primary mirror, a strongly aspheric 0.9 m secondary
and three-lens corrector and has 8 m focal length (Hodapp et al.
2004). The telescope illuminates a diameter of 3.3 deg and
the “GigaPixel Camera” (Tonry & Onaka 2009) comprises a
total of 60 4800 × 4800 pixel detectors, with 10 μmpixels
that subtend 0.258 arcsec (for more details, see Magnier et al.
2013). The PS1 filter system is described in Tonry et al. (2012b),
and is similar to but not identical to the SDSS griz (York et al.
2000) filter system. However, it is close enough that cataloged
cross-matching between the surveys can identify high amplitude
transients. In this paper, we will convert all the PS1 filter
magnitudes g
P1
r
P1
i
P1
z
P1
y
P1
to the SDSS AB magnitude system
as the bulk of the follow-up data were taken in SDSS-like filters
(see Section 3 for more details).
The PS1 telescope is operated by the PS1 Science Consortium
(PS1SC) to undertake several surveys, with the two major ones
being the “Medium Deep Field” survey (e.g., Botticella et al.
2010; Tonry et al. 2012a; Gezari et al. 2012; Berger et al. 2012)
which was optimized for transients (allocated around 25% of
the total telescope time) and the wide-area 3π survey, allocated
around 56% of the available observing time. As described in
Magnier et al. (2013), the goal of the 3π survey is to observe the
portion of the sky north of −30 deg declination, with a total of 20
exposures per year across all five filters for each field center. The
3π survey plan is to observe each field center four times in each
of g
P1
r
P1
i
P1
z
P1
y
P1
during a 12 month period, although this can
2
The Astrophysical Journal, 770:128 (28pp), 2013 June 20 Inserra et al.
be interrupted by bad weather. As described by Magnier et al.
(2013), the four epochs in a calendar year are typically split into
two pairs called Transient Time Interval (TTI) pairs which are
single observations separated by 20–30 minutes to allow for the
discovery of moving objects. The temporal distribution of the
two sets of TTI pairs is not a well-defined and straightforward
schedule. The blue bands (g
P1
, r
P1
, i
P1
) are scheduled close
to opposition to enhance asteroid discovery with g
P1
and r
P1
being constrained in dark time as far as possible. The z
P1
and
y
P1
filters are scheduled far opposition to optimize for parallax
measurements of faint red objects. Although a large area of sky
is observed each night (typically 6000 deg
2
), the moving object
and parallax constraints mean the 3π survey is not optimized for
finding young, extragalactic transients in a way that the PTF and
La Silla-QUEST projects are. The exposure times at each epoch
(i.e., in each of the TTI exposures) are 43 s, 40 s, 45 s, 30 s,
and 30 s in g
P1
r
P1
i
P1
z
P1
y
P1
. These reach typical 5σ depths of
roughly 22.0, 21.6, 21.7, 21.4, and 19.3 as estimated from point
sources with uncertainties of 0.
m
2 (in the PS1 AB magnitude
system described by Tonry et al. 2012b).
The PS1 images are processed by the Pan-STARRS1 Im-
age Processing Pipeline (IPP), which performs automatic bias
subtraction, flat fielding, astrometry (Magnier et al. 2008), and
photometry (Magnier 2007). These photometrically and astro-
metrically calibrated catalogs produced in MHPCC are made
available to the PS1SC on a nightly basis and are immediately
ingested into a MySQL database at Queen’s University Belfast.
We apply a tested rejection algorithm and cross match the PS1
objects with SDSS objects in the DR7 catalog
14
(Abazajian et al.
2009). We apply the following selection filters to the PS1 data
(all criteria must be simultaneously fulfilled).
1. PS1 source must have 15 <g
P1
< 20 or 15 <r
P1
< 20 or
15 <i
P1
< 20 or 15 <z
P1
< 20.
2. SDSS counterpart must have 18 <r
SDSS
< 23.
3. Distance between PS1 source and SDSS source must
be <3 arcsec.
4. PS1 mag must be 1.5 mag brighter than SDSS (in the
corresponding filter).
5. The PS1 object must be present in both TTI pairs and
the astrometric recurrences be <0.
3. Objects with multiple
detections must have rms scatter <0.
1.
6. The PS1 object must not be in the galactic plane (|b| > 5
◦
).
All objects are then displayed through a Django-based inter-
face to a set of interactive Web sites, and human eyeballing and
checking takes place. We use the star–galaxy separation in SDSS
to guide us in what may be variable stars (i.e., stellar sources
in SDSS which increase their luminosity) or extragalactic tran-
sients (i.e., quasi-stellar objects (QSOs), active galactic nuclei
(AGNs), and SNe). While the cadence of the PS1 observations
is not ideal for detections of young SNe we have found many
SNe in intrinsically faint galaxies. As of 2013 January, spec-
troscopically confirmed objects include 34 QSOs or AGNs and
41 SNe. Several of these have been confirmed as SL-SNe. Pas-
torello et al. (2010) presented the data of SN 2010gx recovered
in 3π images, and in many cases the same object is detected by
the Catalina Real-Time Transient Survey (CSS/MSS) and PTF.
As we are not doing difference imaging and only comparing to
objects in the SDSS footprint, there are some cases where ob-
jects are reported by PTF or CRTS and interesting pre-discovery
epochs are available in PS1. As 3π difference imaging is not
14
http://www.sdss.org/dr7/
being carried out routinely, we often use the PTF and CRTS
announcements to inform a retrospective search. In this paper,
we present five SL-SNe Ic which were either detected through
the PS1 FGSS, or were announced in the public domain. A sixth
object (PTF12dam≡PS1-12arh) is discussed in a companion
paper (M. Nicholl et al., in preparation). In all five cases follow-
up imaging and spectroscopy was carried out as discussed
below.
For all the SNe listed here (and throughout this paper) we
adopt a standard cosmology with H
0
= 72 km s
−1
, Ω
M
= 0.27,
and Ω
λ
= 0.73. There is no detection of Na i interstellar medium
(ISM) features from the host galaxies, nor do we have any
evidence of significant extinction in the hosts from the SNe
themselves. This suggests that the absorption in host is low and
we assume that extinction from the host galaxies is negligible.
Although we do detect Mg ii ISM lines from the hosts in some
cases, there is no clear correlation with these line strengths
and line of sight extinction. In all cases only the Milky Way
foreground extinction was adopted.
2.2. PTF10hgi
PTF10hgi was first discovered by PTF on 2010 May 15.5
and announced on 2010 July 15 (Quimby et al. 2010). The
spectra taken by PTF on May 21.0 UT and June 11.0 UT
were reported as a blue continuum with faint features typical of
SL-SNe Ic. Another spectrum obtained by PTF on July 7.0 UT
was similar to PTF09cnd at three weeks past peak brightness.
Initiated by Quimby et al. (2010), ultraviolet (UV) observations
were obtained with Swift+UVOT in 2010 July, and we analyze
those independently later in Section 3. PTF10hgi lies outside the
SDSS DR9
15
area (Ahn et al. 2012), hence was not discovered
by our PS1 FGSS software. However, after the announcement
(Quimby et al. 2010), we recovered it in PS1 images taken (in
band r
P1
) on 2010 May 18 and on four other epochs around peak
magnitude (in bands g
P1
r
P1
i
P1
), listed in Table A1.
We detect a faint host galaxy in deep griz-band images
taken with the William Herschel Telescope on 2012 May 26
and the Telescopio Nazionale Galileo on 2012 May 28. At a
magnitude r = 22.01 ± 0.07, this is too faint to affect the
measurements of the SN flux up to +90 days. There are no
host galaxy emission lines detected in our spectra, hence the
redshift is determined through cross-correlation of the spectra
of PTF10hgi with other SNe at confirmed redshift indicating a
redshift of z = 0.100 ± 0.014, corresponding to a luminosity
distance of d
L
∼ 448 Mpc. The Galactic reddening toward the
SN line of sight is E(B − V ) = 0.09 mag (Schlegel et al. 1998).
2.3. SN 2011ke
SN 2011ke was discovered in the CRTS (CSS110406:
135058+261642) and PTF surveys (PTF11dij) with the earliest
detections on 2011 April 6 and March 30, respectively (Drake
et al. 2011;Quimbyetal.2011c). We also independently de-
tected this transient in the PS1 FGSS (PS1-11xk) on images
taken on 2011 April 15 (Smartt et al. 2011). However, earlier
PS1 data show that we can determine the epoch of explosion to
around 1 day, at least as far as the sensitivity of the images allow.
On MJD 55649.55 (2011 March 29.55 UT) a PS1 image (r
P1
=
40 s) shows no detection of the transient to r 21.17 mag.
Quimby et al. (2011c) report the PTF detection on 2011 March
30 (MJD = 55650) the night after the PS1 non-detection at
15
http://www.sdss3.org/dr9/
3
The Astrophysical Journal, 770:128 (28pp), 2013 June 20 Inserra et al.
g 21. PS1 detections then occurred one and three days af-
ter this on 55651.6 and 55653.6 (in i
P1
and r
P1
), respectively.
The photometry is given in Table A2. This is the best constraint
on the explosion epoch of SL-SNe to date, allowing the rise
time and light curve shape to be confidently measured. The ob-
ject brightened rapidly, by ∼3 mag in the g band in the first
15 days and 1.7 mag in the subsequent 20 days. It was classified
as SL-SNe Ic by both Drake et al. (2011) and Quimby et al.
(2011c); their spectra obtained on May 8.0 and 11.0 UT, respec-
tively, showed a blue continuum with faint features, similar to
PTF09cnd about one week past maximum light (Quimby et al.
2011c).
We found a nearby source in the SDSS DR9 catalog (g =
21.10 ± 0.08, r = 20.71 ± 0.08), which is the host galaxy as
confirmed by deep griz images taken with the William Herschel
Telescope on 2012 May 26 at a magnitude g = 21.18 ± 0.05,
r = 20.72 ± 0.04. The host emission lines set the SN at
z = 0.143, equivalent to a luminosity distance of d
L
= 660 Mpc.
The Galactic reddening toward the position of the SN is
E(B − V ) = 0.01 mag (Schlegel et al. 1998).
2.4. PTF11rks
PTF11rks was first detected by PTF on 2011 December
21.0 UT (Quimby et al. 2011a). Spectra acquired on December
27.0 UT and 31.0 UT showed a blue continuum with broad
features similar to PTF09cnd at maximum light, confirming it as
an SL-SN Ic. A non-detection in the r band on December 11 UT
prior to discovery is also reported, setting a limit of >20.6 mag
at this epoch. Quimby et al. (2011a) detailed a brightening of
0.8 mag in the r band in the first six days after the discovery.
Prompt observations with Swift revealed a UV source at the
optical position of the SN, but no source was detected in X-rays
at the same epochs. There are no useful early data from PS1 for
this object.
The host galaxy is listed in the SDSS DR9 catalog with
g = 21.59 ± 0.11 mag and r = 20.88 ± 0.10 mag. Confir-
mation of these host magnitudes as achieved with our deep
gr-band images taken with the William Herschel Telescope
on 2012 September 22 at a magnitude g = 21.67 ± 0.07 and
r = 20.83 ± 0.05. The emission lines of the host and narrow
absorptions consistent with Mg ii λλ2796, 2803 doublet locate
the transient at z = 0.19, corresponding to a luminosity distance
of d
L
= 904 Mpc. The Galactic reddening toward the position
of the SNe is E(B − V ) = 0.04 mag (Schlegel et al. 1998).
2.5. SN 2011kf
SN 2011kf was first detected by CRTS (CSS111230:
143658+163057) on 2011 December 30.5 UT (Drake et al.
2012). The spectra taken by Prieto et al. (2012) on 2012 January
2.5 UT and 17.5 UT reveal a blue continuum with absorption
feature typical of a luminous Type Ic SN.
The closest galaxy is ∼23
S/W of the object position and is
hence too far to be the host. There is no obvious host coincident
with the position of this SN in SDSS DR9. We detect a faint host
galaxy in deep gri-band images taken with the William Herschel
Telescope on 2012 July 20. At a magnitude r = 23.94 ± 0.20,
this is too faint to affect the measurements of the SN flux
out to +120 days. The redshift of the object has been determined
to be z = 0.245 from narrow Hα and [O iii], equivalent to
a luminosity distance of d
L
= 1204 Mpc. The foreground
reddening is E(B − V ) = 0.02 mag from Schlegel et al. (1998).
2.6. SN 2012il
SN 2012il was first detected in the PS1 FGSS on 2012 January
19.9 UT (Smartt et al. 2012) and also independently discovered
by CRTS on 2012 January 21 (CSS120121:094613+195028;
Drake et al. 2012). On January 29 UT we obtained a spectrum of
the SN, which resembled SN 2010gx four days after maximum
light. The merged PS1 and CRTS data suggest a rise time of more
than two weeks, different from that of SN 2010gx (Pastorello
et al. 2010) but similar to PS1-11ky (Chomiuk et al. 2011). An
initial analysis of observations from Swift revealed a marginal
detection in the u, b, v, and uvm2 filters, with no detection in
the uvw1 and uvw2 filters, or in X-rays (Margutti et al. 2012).
However, our re-analysis of the Swift data reveals a detection
above the 3σ level in the uvw1 and uvw2 filters (see Table A7).
No radio continuum emission from the SN was detected by the
EVLA (Chomiuk et al. 2012).
In our astrometrically calibrated images the SN coordi-
nates are α = 09
h
46
m
12.
s
91 ± 0.
s
05, δ = +19
◦
50
28.
70 ±
0.
05 (J2000). This is within 0.
12 of the faint galaxy
SDSS J094612.91+195028.6 (g = 22.13 ± 0.08, r = 21.46 ±
0.07). The emission lines of Hα,Hβ and [O iii] from the host
give a redshift of z = 0.175, corresponding to a luminosity
distance of d
L
= 825 Mpc. The Galactic reddening toward
SN 2012il given by Schlegel et al. (1998)isE(B − V ) =
0.02 mag, three times lower than the value reported by Margutti
et al. (2012).
3. FOLLOW-UP IMAGING AND PHOTOMETRY
Optical and near-infrared (NIR) photometric monitoring
of the five SNe was carried out using the telescopes and
instruments listed in Appendix A. The main sources of our
photometric follow-up were the SDSS-like griz filters in the
cameras at the Liverpool Telescope (RATCam), the William
Herschel Telescope (ACAM), and the Faulkes North Telescope
(MEROPE). Further data in BV and JHK filters were taken for
some of the SNe with the EKAR 1.8 m Telescope (AFOSC),
the ESO NTT (EFOSC2) and the Nordic Optical Telescope
(NOTCam). Swift+UVOT observations have been taken for four
out of five SNe in the UV filters uvw2, uvm2, and uvw1 (and
for three SNe in the Swift u filter) and we analyzed these publicly
available data independently. Aside from SN 2011ke, ground-
based SDSS-like u observations were sparse, and for two SNe
of our sample nonexistent.
Observations were reduced using standard procedures in the
IRAF
16
environment. The magnitudes of the SNe, obtained
through a point-spread function fitting, were measured on the
final images after overscan correction, bias subtraction, flat field
correction, andtrimming. When necessarywe applied atemplate
subtraction technique (see Figure 1) on later epochs (through the
HOTPANTS
17
package based on the algorithm presented in
Alard 2000). The instruments used to obtain reference im-
ages were the William Herschel Telescope and the Telescopio
Nazionale Galileo. The same images were used to measure the
host magnitudes and listed in Appendix A (Tables A1–A3, A5,
and A6) and labeled as “Host.” When we did not have tem-
plate images, we used SDSS images as templates to remove the
flux of the host. The magnitudes of SDSS stars in the fields of
16
Image Reduction and Analysis Facility (IRAF) is distributed by the
National Optical Astronomy Observatory, which is operated by the
Association of Universities for Research in Astronomy, Inc., under cooperative
agreement with the National Science Foundation.
17
http://www.astro.washington.edu/users/becker/hotpants.html
4
![Table 3 Observed Blackbody Temperature, Expansion Photospheric Velocities from Fe ii λ5169, Mg ii λ4481, and O i λ7775 in our SL-SNe Sample on the Left; Expansion Velocities from Ca ii H&K and Mg i] λ4571 on the Right](/figures/table-3-observed-blackbody-temperature-expansion-b5w2lqly.webp)