Direct evidence for a supernova interacting with a large amount of hydrogen-free circumstellar material

TLDR: In this paper, a Type Ic SNe lacking spectroscopic signatures of H and He was observed to have a slowly-declining light curve and a blue quasi-continuum and narrow oxygen emission lines.

Abstract: We present our observations of SN 2010mb, a Type Ic SN lacking spectroscopic signatures of H and He. SN 2010mb has a slowly-declining light curve ($\sim600\,$days) that cannot be powered by $^{56}$Ni/$^{56}$Co radioactivity, the common energy source for Type Ic SNe. We detect signatures of interaction with hydrogen-free CSM including a blue quasi-continuum and, uniquely, narrow oxygen emission lines that require high densities ($\sim10^9$cm$^{-3}$). From the observed spectra and light curve we estimate that the amount of material involved in the interaction was $\sim3$M$_{\odot}$. Our observations are in agreement with models of pulsational pair-instability SNe described in the literature.

Figures

Figure 5. SN 2010mb line profiles. Comparing the nebular emission lines from Mg i] (top panels) and [Ca ii] (bottom panels), we see a flat-topped profile in the former line, usually interpreted as a signature of non-spherical geometry (Mazzali et al. 2007; Maeda et al. 2008; Mazzali et al. 2005; Modjaz et al. 2008; Taubenberger et al. 2009). The different line shapes of [Ca ii] and Mg i] would, in this case, indicate a non-uniform spatial abundance structure.

Table 3 Nebular Model Composition

Figure 1. Top left: an image of SN 2010mb taken with the P48 on 2010 June 10 UT (MJD 55357.69). Top right: reference image for SN 2010mb. Bottom left: the SN 2010mb image after reference subtraction. Residuals from host galaxy contamination are negligible, as is apparent in the image. Bottom right: a zoomed image of SN 2010mb obtained on 2011 March 4 UT (MJD 55624.11) with LRIS mounted on the Keck-I 10 m telescope. The offset of the SN from the host center (1.′′3 W and 2.′′2 N) is clearly seen.

Figure 6. SN 2010mb spectral decomposition. We decompose each spectrum to three components: photospheric and nebular models based on SN 1997ef (Mazzali & Lucy 1993; Lucy 1999; Mazzali et al. 2000, 2004, 2007); and an interaction component based on comparison to the continuum shape (H lines excluded) of the spectrum of SN 2005cl, a hydrogen-rich Type IIn SN, with a prominent blue quasi-continuum originating from the SN ejecta interacting with hydrogen-rich CSM (Kiewe et al. 2012). Some of the lines, such as the [O iii] λ5007 and the O i λ7773 recombination lines, are not handled by our modeling code.

Figure 11. Host Galaxy nucleus spectrum. The spectrum was taken on 2012 February 20 UT using LRIS mounted on Keck-I 10 m telescope and is calibrated to r band photometry. Two spectra of SN 2010mb (2011 March 4 and July 5 UT) are given for comparison, showing the different spectral energy distribution between the host galaxy and the SN, and demonstrating that the SN is much bluer than the host, also evident from color comparison of the host (g − r = 0.45; SDSS) and the SN (g − r = −0.93 on 2010 July 10 UT and g − r = −2.73 on 2011 January 12 UT). Spectra are available in digital form from the Weizmann Interactive Supernova Data Repository (WISeREP; Yaron & Gal-Yam 2012; http://www.weizmann.ac.il/astrophysics/wiserep/).

Figure 10. Characterizing the interacting CSM. Left: a CSM density profile derived from the LC of SN 2010mb, assuming a symmetric spherical CSM distribution (solid points; see text for details). The data are best fitted by a power law profile of n ∝ r−2.6 (blue line). For comparison, an n ∝ r−2 profile is also presented (red line). Right: CSM column density derived by integrating over the density profile shown in the left panel. The high column density explains why X-ray photons have not been detected.

Full text

The Astrophysical Journal, 785:37 (13pp), 2014 April 10 doi:10.1088/0004-637X/785/1/37
C

2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
SN 2010MB: DIRECT EVIDENCE FOR A SUPERNOVA INTERACTING WITH A LARGE
AMOUNT OF HYDROGEN-FREE CIRCUMSTELLAR MATERIAL
Sagi Ben-Ami
1
, Avishay Gal-Yam
1,16
, Paolo A. Mazzali
2,3,4
, Orly Gnat
5
, Maryam Modjaz
6
, Itay Rabinak
1
,
Mark Sullivan
7
, Lars Bildsten
8
, Dovi Poznanski
9
, Ofer Yaron
1
, Iair Arcavi
1
, Joshua S. Bloom
10,11
, Assaf Horesh
12
,
MansiM.Kasliwal
13
, Shrinivas R. Kulkarni
12
, Peter E. Nugent
10,11
, Eran O. Ofek
1
, Daniel Perley
12
,
Robert Quimby
14
, and Dong Xu
15
1
Department of Particle Physics and Astrophysics, The Weizmann Institute of Science, Rehovot 76100, Israel; sagi.ben-ami@weizmann.ac.il
2
Astrophysics Research Institute, Liverpool John Moores University. Liverpool L3 5RF, UK
3
Max-Planck-Institut fur Astrophysik, Karl-Schwarzschildstr. 1, D-85748 Garching, Germany
4
INAF-Osservatorio Astronomico, vicolo dell’Osservatorio, 5, I-35122 Padova, Italy
5
Racah Institute of Physics, The Hebrew University, 91904 Jerusalem, Israel
6
Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, room 529, New York, NY 10003, USA
7
Department of Physics (Astrophysics), University of Oxford, DWB, Keble Road, Oxford, OX1 3RH, UK
8
Kavli Institute for Theoretical Physics and Department of Physics Kohn Hall, University of California, Santa Barbara, CA 93106, USA
9
School of Physics and Astronomy, Tel-Aviv University, Tel Aviv 69978 Israel
10
Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
11
Physics Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
12
Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
13
Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA
14
Kavli IPMU, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8583, Japan
15
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
Received 2013 September 17; accepted 2014 February 16; published 2014 March 24
ABSTRACT
We present our observations of SN 2010mb, a Type Ic supernova (SN) lacking spectroscopic signatures of H
and He. SN 2010mb has a slowly declining light curve (LC) (∼600 days) that cannot be powered by
56
Ni/
56
Co
radioactivity, the common energy source for Type Ic SNe. We detect signatures of interaction with hydrogen-free
circumstellar material including a blue quasi-continuum and, uniquely, narrow oxygen emission lines that require
high densities (∼10
9
cm
−3
). From the observed spectra and LC, we estimate that the amount of material involved
in the interaction was ∼3 M

. Our observations are in agreement with models of pulsational pair-instability SNe
described in the literature.
Key words: stars: mass-loss – stars: Population III – supernovae: general
Online-only material: color figures, machine-readable table
1. INTRODUCTION
A massive star with an initial mass above ∼8 M

ends its
life in an explosion that destroys the star, leaving a neutron star
(NS) or a black hole (BH) as a remnant (Heger et al. 2003).
This explosion is triggered by iron photo-disintegration and
loss of internal energy causing the star to undergo a gravi-
tational core-collapse (CC) supernova (SN; e.g., Woosley &
Janka 2005).
At an earlier stage in its evolution, an extremely massive
star (initial mass above ∼100 M

) will go through a phase of
electron–positron generation in its core (Barkat et al. 1967;
Rakavy & Shaviv 1968; Heger et al. 2003; Waldman 2008;
Chatzopoulos & Wheeler 2012; Yusof et al. 2013). The pair
production will render the star unstable, with two possible
outcomes: (1) the star will end its life in an explosion that
ejects the entire mass of the star and leaves no remnant at
all, a pair-instability supernova (PISN; progenitor mass above
∼140 M

). (2) The star will eject matter in a series of eruptions,
a pulsation pair-instability (PPI) event (progenitor mass between
∼100–140 M

), thus reducing the core mass until it reaches
hydrostatic equilibrium and returns to the normal evolution track
of massive stars, ending its life due to CC (Heger & Woosley
2002; Heger et al. 2003; Woosley et al. 2007; Waldman 2008;
16
Kimmel Investigator.
Chatzopoulos & Wheeler 2012). Several examples of possible
PISN events have been observed in recent years (SN 2007bi
and PTF10nmn; Gal-Yam et al. 2009, Gal-Yam 2012, O. Yaron
et al. 2014, in preparation; though see Nicholl et al. 2013). Only
indirect evidence has so far been presented for a PPI event (e.g.,
SN 2006gy and SN 2006jc; Woosley et al. 2007; Pastorello et al.
2008a; Chugai 2009).
For both CC SNe and PISNe, the energy source at late
times is the radioactive decay of
56
Co−→
56
Fe, with a half-
life of 77 days. Other energy sources that can contribute to the
optical display of an SN are hydrogen recombination in the
expanding ejecta (Type II-P SN; Popov 1993), and an internal
engine such as a nascent magnetar (Kasen & Bildsten 2010;
Woosley 2010; Mazzali et al. 2009) or accretion by a stellar BH
(Patnaude et al. 2011). In some cases, interaction of SN ejecta
with circumstellar material (CSM), most commonly observed
through narrow hydrogen lines in Type IIn SNe (e.g., Schlegel
1990; Kiewe et al. 2012), will inject additional energy into the
optical display.
Here, we describe SN 2010mb (PTF10iue), an SN lacking
signatures of either hydrogen or helium (Type Ic), with long-
lasting emission powered by interaction of the SN ejecta with
a large mass of hydrogen-free CSM. Section 2 describes our
observations; and Section 3 presents our results and analysis. In
Section 4, we discuss possible scenarios, with an emphasis on
the PPI option. Conclusions are given in Section 5.
1

The Astrophysical Journal, 785:37 (13pp), 2014 April 10 Ben-Ami et al.
Figure 1. Top left: an image of SN 2010mb taken with the P48 on 2010 June 10 UT (MJD 55357.69). Top right: reference image for SN 2010mb. Bottom left: the
SN 2010mb image after reference subtraction. Residuals from host galaxy contamination are negligible, as is apparent in the image. Bottom right: a zoomed image of
SN 2010mb obtained on 2011 March 4 UT (MJD 55624.11) with LRIS mounted on the Keck-I 10 m telescope. The offset of the SN from the host center (1.

3Wand
2.

2 N) is clearly seen.
2. OBSERVATIONS
2.1. Discovery
On 2010 April 10 UT (MJD 55296.76) the Palomar Transient
Factory (PTF; Law et al. 2009, Rau et al. 2009) detected SN
2010mb at R.A. = 16
h
00
m
23.
s
103 and decl. = 37
◦
44

57

(de-
tection magnitude 21.47 ± 0.2inr band) using the CFH12K sur-
vey camera mounted on the 48

Oschin Schmidt telescope at the
Palomar observatory(P48). Analysis of previous images showed
the SN was visible on 2010 March 18 UT (MJD 55273.96), at a
magnitude of 22.2 ± 0.54 in the r band. The object is located on
the edge of the galaxy SDSS J160023.23+374454.8 at a redshift
z = 0.1325. Figure 1 shows detection, reference, and subtracted
images of the SN.
Prior to 2010 March 18 UT, the galaxy was imaged 10 times
by the PTF survey between 2009 May 18 and August 21 UT
(MJD 54969-55064), with no evidence for the SN or any activity
in its vicinity.
We classified SN 2010mb as a Type Ic SN based on a spectrum
lacking signatures of either hydrogen or helium taken on 2010
June 8 UT (MJD 55355. Figures 2 and 3; Ben-Ami et al. 2012).
2.2. Photometry
SN 2010mb, discovered near the P48 detection limit, was
intermittently detected during the first 50 days after its discov-
ery,
17
until it became continuously visible on 2010 May 31 UT
17
We define a detection as a 5σ signal above the zero point photon count. In
cases where the object did not pass this criterion, 2010 April 30 and May
12 UT (MJD 55316 and MJD 55328, respectively), the signals were 4σ and
2.6σ above the zero point photon count, respectively.
(MJD 55347.71) at an apparent magnitude of 20.85 ± 0.12 in
the r band.
Photometry of SN 2010mb was obtained by the P48 (Law
et al. 2009; Rau et al. 2009), the gamma-ray burst camera
(Cenko et al. 2006) mounted on the Palomar 60

telescope
(P60), the Large Format Camera mounted on the Palomar
200

Hale telescope (P200), and the Low Resolution Imaging
Spectrograph (LRIS) mounted on the 10 m Keck-I telescope
(Oke et al. 1995). Data were reduced using the MKDIFFLC
photometry routine (Gal-Yam et al. 2004, 2008), except for P48
data reduced using point-spread function (PSF) photometry on
image subtractions.
18
The PTF data processing is discussed in
Laher (2014
19
), while the photometric calibration is discussed
in Ofek et al. (2012a; 2012b). We adopt a distance modulus of
39.07 mag, based on measured redshift from the SN spectrum
(assuming H
0
= 67.3kms
−1
Mpc
−1
and Ω
m
= 0.315;
Planck Collaboration et al. 2013), corresponding to a luminosity
distance of ≈650.46 Mpc, a Galactic extinction correction
of E(B − V ) = 0.013 mag (A
r
= 0.033 mag; Schlafly
& Finkbeiner 2011; see NED,
20
as well as Section 3.6.)
Photometric results are given in Table 1 and plotted in Figure 4.
No correction for the host extinction is applied. The lack
of strong interstellar medium (ISM) absorption and the blue
18
Image subtraction using previous images of the same field of view taken
with the same instrument during 2009 as references was carried out, followed
by forced PSF photometry and absolute calibration to the SDSS catalog as
done, e.g., in Ofek et al. (2013).
19
See also Laher et al. 2012 for details on the Aperture Photometry Tool.
20
NASA/IPAC Extragalactic Database (NED) is operated by the Jet
Propulsion Laboratory, California Institute of Technology, under contract with
the National Aeronautics and Space Administration.
2

The Astrophysical Journal, 785:37 (13pp), 2014 April 10 Ben-Ami et al.
1
3
1
3
f
λ
[10
−17
erg s
−1
cm
−2
Ang
−1
]
1
3
1
3
0.2
0.4
4000 5000 6000 7000 8000 9000
0.25
0.75
Rest Frame Wavelength [Ang]
2010 Nov 1
(MJD 55501)
2011 Jul 5
(MJD 55747)
2011 Mar 4
(MJD 55624)
2010 Sep 5
(MJD 55444)
2010 Jul 8
(MJD 55385)
2010 Jun 8
(MJD 55355)
Figure 2. SN 2010mb spectra. No signs of hydrogen lines (emission or absorption) or helium lines are seen, indicating a Type Ic SN. Late-time spectra (2011 March 4
and July 5 UT) are dominated by a blue quasi-continuum component. Spectra are available in digital form from the Weizmann Interactive Supernova Data Repository
(WISeREP; Yaron & Gal-Yam 2012; http://www.weizmann.ac.il/astrophysics/wiserep/).
4,000 5,000 6,000 7,000 8,000 9,000
0
2
4
6
8
10
12
Rest Frame Wavelength [Ang]
f
λ
[Arbitrary]
SN 2007gr
+54d
SN 2007bi
+414d
SN 2010mb
SN 1997ef
+89d
SN 1995F
+90d
2010 Sep 5
2010 Jun 8
MgI]+
[SI]
[OIII]
OI+
[SI]
CaII
CaII+
[CI]
NaI
[SiI]
FeII
CaII
[SII]
FII
Figure 3. SN 2010mb spectral classification. Early spectra of SN 2010mb resemble a Type Ic SN at the transition between the photospheric and nebular phases as late
as ∼170 days after discovery (i.e., some photospheric features were still observed in the spectrum taken on 2010 September 5 UT, second spectrum from the bottom).
Automatic classification of the spectra taken on 2010 June 8 and July 8 UT using Superfit (Howell et al. 2005) suggests that the best match is to the late-time spectra
of SN 1997ef 89 days after peak magnitude (an energetic Type Ic SN showing late transition from photospheric phase to nebular phase; Mazzali et al. 2004), and SN
1995F 90 days after discovery (a Type Ic SN; Matheson et al. 2001), while automatic classification using SNID (Blondin & Tonry 2011) suggests that the best match
is to SN 2007gr at 54 days after peak magnitude (a “normal” Type Ic; Hunter et al. 2009). This highlights the slow evolution of SN 2010mb, similar to SN 1997ef, and
much slower than a “normal” Type Ic SN like SN 2007gr. The spectra also resemble nebular spectra of SN 2007bi (Gal-Yam et al. 2009).
(A color version of this figure is available in the online journal.)
spectral energy distribution (SED) measured at late times (see
Section 3) argue against a substantial host extinction.
The light curve (LC) displayed a long plateau in r band lasting
∼180 days, followed by a slow decline at a rate of 0.004 mag
day
−1
, while the g band and B band LCs are slowly rising
during the first ∼250 days (Figure 4). The total amount of
energy emitted in the r band over a period of ∼600 days is
∼1.2 × 10
50
erg (an average flux of 1.8 × 10
−13
erg s
−1
cm
−2
).
Assuming a bolometric correction of 10% at early times and
50% at later times based on our spectral decomposition (see
Section 3.2), we estimate a total energy emission of 3.7 ± 0.4 ×
10
50
erg over a period of ∼600 days.
2.3. Spectroscopy
Six spectra of SN 2010mb were obtained (Table 2 and
Figure 2). Data were reduced using standard IRAF and IDL
routines (e.g., Matheson et al. 2000b, Gal-Yam et al. 2007)
3

The Astrophysical Journal, 785:37 (13pp), 2014 April 10 Ben-Ami et al.
5300 5400 5500 5600 5700 5800 5900 6000
−20
−19
−18
−17
−16
−15
−14
MJD−50000 [day]
Absolute magnitude [mag]
SN 2010mb r−band
SN 2010mb g−band
SN 2010mb B−band
SN 2010mb i−band
+0.5mag
SN 2007bi +4mag
Type Ic
*
+1mag
Estimated
Explosion
Figure 4. Photometry of SN 2010mb. The r band LC rises by 1.3 mag during the first ∼25 days, and then settles onto a plateau lasting ∼180 days at an absolute
magnitude of −18.25 mag (deviations from the plateau, marked by a dashed red line, are not statistically significant). Following the plateau, the LC drops by 0.9mag
in less than 23 days, followed by a period of slow decline at a rate of 0.004 mag day
−1
, which is less than half the decline rate of the
56
Ni/
56
Co powered SNe, during
the next 350 days. Photometry in the g band and B band showed a slow increase in flux during the first 250 days of this event. The dashed vertical lines indicate a
spectrum was taken on that day. The LCs of SLSN-R SN 2007bi in the R band (candidate pair instability event; Gal-Yam et al. 2009), and of an average Type Ic SN
template in the R band (Drout et al. 2011), are shown for comparison. On 2011 December 21 UT (MJD 55916), the SN was no longer visible in deep images taken
with the LFC. Deeper images taken with LRIS on 2012 January 26 UT (MJD 55952.09) set a limiting absolute magnitude of −14.1 at that time (triangles).
(A color version of this figure is available in the online journal.)
Tab le 1
SN 2010mb Photometry
Date (MJD) Instrument Exposure Time Apparent Magnitude Magnitude Error Filter
(s) (mag) (mag)
55273.96 P48
a
2 × 200 22.20 0.54 r
55296.76 P48 2 × 200 21.47 0.20 r
55384.84 P60
b
360 21.00 0.10 r
55477.64 LFC
c
900 20.78 0.15 r
55624.11 LRIS
d
120 22.60 0.14 r
Notes. Digital dataare available from the Weizmann Interactive SupernovaData Repository (WISeREP; Yaron & Gal-Yam
2012; http://www.weizmann.ac.il/astrophysics/wiserep/).
a
Palomar 48

Oschin Schmidt telescope.
b
Palomar 60

Oscar Mayer telescope.
c
Large Format Camera mounted on the Hale 200

telescope.
d
Low Resolution Imaging Spectrograph mounted on the Keck-I 10 m telescope.
(This table is available in its entirety in a machine-readable form in the online journal. A portion is shown here for
guidance regarding its form and content.)
and were smoothed with a three-pixel boxcar. The observed
spectra are deredshifted by z = 0.1325, where the redshift
was determined using a χ
2
minimization with an absorption-
line template (Howell et al. 2005; Galactic lines identification
in later spectra, e.g., 2012 February 20 spectrum, confirms
our redshift determination). Spectra are calibrated to the gri
P48/P60 photometry (2010 June 8, July 8, and November
1 UT), to an extrapolation of the gri P48/P60 photometry
(2010 September 5 UT), and to LFC r band photometry (2011
March 4 and July 5 UT). A spectrum of the host galaxy
nucleus was taken on 2012 February 20 UT using LRIS (see
Section 3.6).
3. ANALYSIS
3.1. Classification and Evolution
The first three spectra of SN 2010mb (2010 June 8, July 8,
and September 5 UT) resemble a Type Ic SN at the transition
between photospheric and nebular phase as late as ∼170 days
after discovery (i.e., photospheric features observed in the
spectrum taken on 2010 September 5 UT, Figure 2). Automatic
classification using Superfit (Howell et al. 2005) of the spectra
taken on 2010 June 8 and July 8 UT suggests that the best match
is to the late-time spectra of SN 1997ef 89 days after peak
magnitude (an energetic Type Ic SN showing late transition
4

The Astrophysical Journal, 785:37 (13pp), 2014 April 10 Ben-Ami et al.
Tab le 2
Spectroscopy Log
Date (MJD) Telescope Instrument Exposure Time Grism/Grating Slit
(sec) (lpm)
2010 Jun 8 (55355)
a
Keck-I LRIS 600 400/400
b
1

2010 Jul 8 (55385) Keck-I LRIS 750 400/400 1

2010 Sep 5 (55444) Keck-I LRIS 750 400/400 1

2010 Nov 1 (55501) Keck-I LRIS 750 400/400 1

2011 Mar 4 (55624) Keck-I LRIS 900 400/400 1

2011 Jul 5 (55747) Keck-II DEIMOS
c
1200 600 0.

7
2012 Feb 20 (55977)
d
Keck-I LRIS 1200 400/400 1

Date (MJD) Resolution Airmass Paralactic Angle Position Angle Spec. Standard
(Å)
2010 Jun 8 (55355) 1.09/1.16 1.38 −75
◦
27
◦
BD+28 4211
2010 Jul 8 (55385) 1.09/1.16 1.01 134
◦
270
◦
BD+26 2606
2010 Sep 5 (55444) 1.09/1.16 1.24 −90
◦
19
◦
BD+28 4211
2010 Nov 1 (55501) 1.09/1.16 1.55 −90
◦
−8
◦
BD+28 4211
2011 Mar 4 (55624) 1.09/1.16 1.29 14
◦
270
◦
BD+28 4211
2011 Jul 5 (55747) 0.65 1.07 42
◦
256
◦
BD+28 4211
2012 Feb 20 (55977) 1.09/1.16 1.18 238
◦
328
◦
BD+26 2606
Notes.
a
The CBET classifying this object (Ben-Ami et al. 2012) erroneously lists the Palomar 200

Hale telescope as that used
for the spectrum taken on 2010 June 8 UT. The details here supersede this publication.
b
The Low Resolution Imaging Spectrograph has two arms (blue and red). Each arm is equipped with a different grating
and, therefore, a different resolution.
c
Deep Imaging Multi-Object Spectrograph Faber et al. (2003); filter: GG455.
d
Host Galaxy spectrum.
from photospheric phase to nebular phase; Mazzali et al. 2004),
and SN 1995F 90 days after discovery (a Type Ic SN; Matheson
et al. 2001), while automatic classification using SNID (Blondin
& Tonry 2011) suggests that the best match is to SN 2007gr
at 54 days after peak magnitude (a “normal” Type Ic; Hunter
et al. 2009), Figure 3. This highlights the slow evolution of SN
2010mb, similar to SN 1997ef, and much slower than a “normal”
Type Ic SN like SN 2007gr. The spectra also resemble nebular
spectra of SN 2007bi (PISN; Gal-Yam et al. 2009). Based on
the resemblance between SN 2010mb spectrum taken on 2010
June 8 UT, and SN 1997ef spectrum taken 89 days after peak
magnitude, and assuming a rise time of 20 days (Mazzali et al.
2004), we assume SN 2010mb exploded around 2010 February
23 UT, though this number is highly uncertain.
Early and intermediate spectra (i.e., 2010 June 8 until
November 1 UT) are dominated by blended lines of Ca ii
λλ3933, 3968 and [S ii] λ4069, Mg i] λ4571 and [S i] λ4589,
[O iii] λλ4959, 5007, Fe ii blended lines (5200–5400 Å), [O i]
and Fe ii blended lines (6300–6400 Å), O i λ7773 and [S i]
λ7728, and Ca ii λλ8498, 8542, 8662, and [C i] λ8727. The Na i
D line, [Si i] λ6527, and [Ca ii] λλ7291, 7324 are clearly ob-
served in the spectra as well (line identification is based on the
models described in Section 3.2; Wavelengths are given in rest
frame); see Figure 3. Some of the lines, such as the Mg i] λ4571
line, seem to have an internal structure, while others, such as
the [Ca ii] λλ
7291, 7324 seem to have narrow cores, an indi-
cation for a different spatial distribution of these elements and,
therefore, for a non-spherical geometry; see Figure 5. Late-time
spectra (2011 March 4 and July 5 UT; Figure 2) are dominated
by a blue quasi-continuum component, also reflected in g band
and B band photometry that is slowly rising during the first
∼250 days, a behavior inconsistent with that of a purely hydro-
dynamic radioactive explosion that would show a monotonic
decrease in temperature with time. We therefore conclude that
another energy source other than radioactive
56
Ni decay, the
common energy source powering Type Ic SNe, is driving the
optical display of SN 2010mb at late times.
3.2. Modeling
We model the spectra obtained on 2010 June 8, July 8,
September 5, and 2011 March 4 UT. We start by modeling
the blue quasi-continuum,
21
which seems to be the strongest
component in late-time spectra (2011 March 4 and July 5 UT).
An attempt to fit blackbody profiles at temperatures between
5000–10,000 K to the observed blue quasi-continuum gave
unsatisfactory results. We conclude that the quasi-continuum
is nonthermal in the sense that it is not described well by
a blackbody of any temperature, a behavior also known for
Type IIn SNe (e.g., Kiewe et al. 2012). We therefore use the
spectral continuum derived from observations of SN 2005cl,
a hydrogen-rich Type IIn SN, with prominent blue quasi-
continuum associated with CSM–ejecta interaction. We use the
spectrum taken on 2005 August 13 UT, in which the CSM–ejecta
interaction seems to be the strongest. The spectrum is dominated
by overlapping Fe ii lines, some of which are partially resolved
(Kiewe et al. 2012). After removing the Balmer lines and fitting a
smooth curve to the continuum, we scale the resulting curve to fit
the continuum seen in each of the SN 2010mb observed spectra.
The match between the SN 2010mb blue quasi-continuum at
late times when the blue quasi-continuum is more prominent,
and the model based on the SN 2005cl spectrum, lends credence
to this approach.
After removing the blue quasi-continuum from the four spec-
tra, we compose a photospheric model to match the observed
spectra. SN 1997ef and SN 2010mb both show an extended
21
As the spectra are calibrated to host-subtracted photometry, this component
is unlikely to be residual host contamination.
5

Frequently asked questions

Q1. What are the contributions in "C: " ?

The authors present their observations of SN 2010mb, a Type Ic supernova ( SN ) lacking spectroscopic signatures of H and He. SN 2010mb has a slowly declining light curve ( LC ) ( ∼600 days ) that can not be powered by 56Ni/56Co radioactivity, the common energy source for Type Ic SNe. 

Q2. How is the mass of the nebula scaled?

The mass of each element is scaled linearly with the line strengths, and from the match quality, the authors derive a 50% uncertainty in the derived masses for most of the elements. 

Q3. Who provided the staff, computational resources, and data storage for this project?

The National Energy Research Scientific Computing Center, supported by the Office of Science of the U.S. Department of Energy, provided staff, computational resources, and data storage for this project. 

Q4. What is the effect of a magnetar on SN LCs?

very highly magnetic (B > 1014 G) and rapidly rotating (Ps ≈ 2–5 ms) NSs, generated at the time of SN explosion, can have a large impact on SN LCs (Mazzali et al. 

Q5. What is the expected optical signature of a successful SN?

In case of a successful SN following the CC, the expected optical signature is a long-lasting event, where the SN ejecta will interact with the large amount of CSM ejected in the recent past. 

Q6. How did the authors measure the emission line flux?

The authors detected and measured this emission line flux by fitting a function to the line profile using the standard IRAF procedure splot, as well as a custom MATLAB script, which removes nearby continuum by using a spline function at an area of ±100 Å around the line peak. 

Q7. What is the opacity of the SN 2010mb LC?

In this model, the opacity is approximated by a step function and is constant above the ionization temperature, Tion, and equals zero below that. 

Q8. What is the effect of a non-violent white dwarf merger?

Hachinger et al. (2012) suggest that a non-violent white dwarf merger can culminate in a Type Ia SN interacting with H-/He-free CSM, causing an increase in the observed flux with respect to the flux of a typical Type Ia SN. 

Q9. What is the spectral energy distribution of the r band?

The total amount of energy emitted in the r band over a period of ∼600 days is ∼1.2 × 1050 erg (an average flux of 1.8 × 10−13 erg s−1 cm−2). 

Q10. What is the way to fit the blue quasi-continuum?

An attempt to fit blackbody profiles at temperatures between 5000–10,000 K to the observed blue quasi-continuum gave unsatisfactory results. 

Q11. How much variability did the authors find for the line flux?

The authors verified that the line is not sensitive to varying the parameters in the nebular modeling code (i.e., changing the amount of radiating mass in the nebular phase) and the blue quasi-continuum flux, and the authors found a variability of ∼5% for the line flux. 

Q12. What is the effect of the radiation on the ejecta?

Though the authors remain unsure as to the form(i.e., Poynting flux, particles, or radiation) of the spin-down power, Lp, the authors will assume that the thinning of the ejecta due to expansion will eventually lead to an inefficient coupling and, hence, a reduction in the optical brightness of the event. 

Q13. What is the interacting material composition of Type Ibn SNe?

The interacting material composition is consistent with that of WR winds, i.e., hydrogen and helium for WN progenitors, and helium for WC/WO progenitors (Pastorello et al. 2008b). 

Q14. How do the authors compute the oxygen abundance from these emission lines?

To compute the oxygen abundance from these H ii region emission lines, the authors follow Modjaz et al. (2011 and references therein) and employ the scales of Pettini & Pagel (2004; PP04-O3N2) and of Kewley & Dopita (2002, hereafter KD02), to obtain oxygen abundance values for the host galaxy nucleus of 12 + log(O/H)PP04−O3N2 = 8.39 ± 0.01 and 12 + log(O/H)KD02 = 8.60 ± 0.05, respectively, where the authors consider only statistical uncertainties. 

Q15. What is the spectral evolution of the [O i] 5577 line?

The authors find that the line at [O i] λ5577 reaches peak intensity between 2010 September 5 and November 1 UT (integrated intensity of 7 ± 0.4, 7.8 ± 0.3 × 10−17 erg s−1 cm−2, respectively), while the [O i] λλ6300, 6363 lines are clearly seen in the host galaxy spectrum taken on 2012 February 20 UT. 

Q16. What is the difference between the SEDs of the host galaxy and SN 2010mb?

The authors find that the host galaxy properties derived from the nucleus and fromthe SN position agree with each other within the error bars, with the SN position values having larger errors because of the lower signal-to-noise ratio at the SN position. 

Q17. How many MEs do the authors get for the ejecta mass?

Based on this analytic model, the authors get the following estimation for the ejecta mass, explosion energy, and progenitor radius:Mej ∼ 1160 t4185T 44170v35L−141 κ−10.2 ME 

Q18. What is the name of the event that is suggested as a way to explain an increased,?

another event where interaction of SN ejecta with Hfree CSM was suggested as a way to explain an increased, short lived luminosity is SN 2009dc, an SN interpreted as a ’Super Chandrasekhar’ Type Ia SN.