The Astrophysical Journal Letters, 789:L6 (5pp), 2014 July 1

doi:10.1088/2041-8205/789/1/L6

C 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

DUST FORMATION IN MACRONOVAE
Hajime Takami1,4 , Takaya Nozawa2 , and Kunihito Ioka1,3

1 Institute of Particle and Nuclear Studies, KEK, 1-1, Oho, Tsukuba 305-0801, Japan; takami@post.kek.jp, kunihito.ioka@kek.jp
2 National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan; takaya.nozawa@nao.ac.jp
3 Department of Particle and Nuclear Physics, the Graduate University for Advanced Studies, Tsukuba 305-0801, Japan

Received 2014 March 23; accepted 2014 May 18; published 2014 June 12

ABSTRACT
We examine dust formation in macronovae (as known as kilonovae), which are the bright ejecta of neutron starbinary mergers and one of the leading sites of r-process nucleosynthesis. In light of information about the firstmacronova candidate associated with GRB 130603B, we find that dust grains of r-process elements have difficulty
forming because of the low number density of the r-process atoms, while carbon or elements lighter than iron cancondense into dust if they are abundant. Dust grains absorb emission from ejecta with an opacity even greater thanthat of the r-process elements, and re-emit photons at infrared wavelengths. Such dust emission can potentiallyaccount for macronovae without r-process nucleosynthesis as an alternative model. This dust scenario predicts aspectrum with fewer features than the r-process model and day-scale optical-to-ultraviolet emission.
Key words: binaries: general – dust, extinction – gamma-ray burst: individual (GRB 130603B) – infrared: stars –methods: numerical – stars: neutron
Online-only material: color figuresejecta also interact with circumstellar matter and radiate likesupernova remnants at a later phase (Nakar & Piran 2011; Piranet al. 2013; Takami et al. 2014; Kyutoku et al. 2014).
Different types of nucleosynthesis may take place in theejecta, depending on Ye . While r-process nucleosynthesis occurs
in low Ye ejecta, relatively high Ye (∼0.2–0.5) can be also
realized, which has been discussed exclusively for neutrinodriven winds (e.g., Fernández & Metzger 2013; Rosswog et al.
2014; Surman et al. 2014; Metzger & Fernández 2014; see also
Wanajo et al. 2014 for locally low Ye dynamical ejecta). In suchenvironments, r-process nucleosynthesis is inefficient, but heavy
elements (up to 56 Ni) may be synthesized from the constituent
nucleons of NS matter, e.g., through a series of captures of α
particles by 12 C produced by the triple-α process (e.g., Surman
et al. 2014).
In this Letter, we investigate dust formation in the ejecta
of NSB mergers for the first time. The formation of dust in
macronovae is expected as in supernovae (e.g., Nozawa et al.
2003) because heavy elements may be synthesized and theejecta temperature may be low enough for dust formation. We
demonstrate that the newly formed dust can be responsible
for the opacity of ejecta and its emission can potentially
reproduce the NIR excess of GRB 130603B. Although the
r-process model can explain this macronova, it is based on thelimited observational data. Thus, it is worth considering the dust
scenario (e.g., see Jin et al. 2013 for another possibility).

1. INTRODUCTION
Macronovae are brightening phenomena associated withejecta from the mergers of neutron star binaries (NSBs), i.e.,
neutron-star–neutron star (NS–NS) binaries and black-hole–NS(BH–NS) binaries. In the original macronova model, the luminosity peaks at ∼1 day after the mergers, with an opacity coefficient of the ejecta of κ ∼ 0.1 cm2 g−1 (Li & Paczyński 1998;
Kulkarni 2005; Metzger et al. 2010). Recent studies have shownthat r-process nucleosynthesis occurs efficiently in neutronrich ejecta (low electron fraction Ye ; e.g., Goriely et al. 2011;
Korobkin et al. 2012; Bauswein et al. 2013). The r-process elements, especially lanthanoids, provide a large opacity for ejecta(κ ∼ 10 cm2 g−1 ; Barnes & Kasen 2013; Tanaka & Hotokezaka
2013; Tanaka et al. 2014), so that their luminosity peaks around
10 days (called the r-process model). In both cases, radioactive decay heats the ejecta and powers emission. The r-processmodel successfully reproduces a near-infrared (NIR) macronova
in the afterglow of the short gamma-ray burst (GRB) 130603B(z = 0.356; Berger et al. 2013; Tanvir et al. 2013; Hotokezaka
et al. 2013b). NSB mergers are the most promising sourcesof gravitational waves which are expected to be directly detected by the next generation of interferometers such as the advanced LIGO (Abadie & LIGO Collaboration 2010), advanced
VIRGO (Accadia et al. 2011), and KAGRA (Kuroda & LCGTCollaboration 2010). The electromagnetic detection ofmacronovae improves the localization of gravitational wave
sources; the localization accuracy by photons is much better
than that by the interferometers, ∼10–100 deg2 (e.g., LIGO
Scientific Collaboration et al. 2013).
Recent numerical simulations have revealed that NSB mergers eject significant masses with ∼10−4 M –10−2 M either
dynamically (e.g., Rosswog et al. 1999; Ruffert & Janka 2001;
Hotokezaka et al. 2013a; Bauswein et al. 2013; Kyutoku et al.
2013) and/or by neutrino-driven (e.g., Ruffert et al. 1997;
Rosswog et al. 2003; Dessart et al. 2009; Metzger & Fernández2014) or magnetically driven winds (e.g., Shibata et al. 2011),
which can explain GRB 130603B in the r-process model. The

2. PHYSICAL PROPERTIES OF THE EJECTA
Dust formation depends on the time evolution of gas density
and temperature. We assume uniform ejecta with a temperature
T and density ρ for simplicity. The NIR macronova of GRB
130603B gives only one observational point (Tanvir et al. 2013):
the absolute AB J-band magnitude of M(J )AB = −15.35 att ∼ 7 days after GRB 130603B in the rest frame. Ejecta arelikely in a free expansion phase with a radius of
R = 3.6 × 10

15

4

JSPS Research Fellow.

1

β
0.2




t
cm,
7 days(1)

The Astrophysical Journal Letters, 789:L6 (5pp), 2014 July 1

Takami, Nozawa, & Ioka

where β is the ejecta speed divided by light speed c, and isbasically determined by the escape velocity of NSs. Hereafter,
β = 0.2 is adopted.
We can estimate the effective temperature of the ejecta at
t0 = 7 days as T0 ∼ 2000 K assuming a blackbody radiation,
so that−st
T = T0,(2)
7 daysTable 1
Grain Species Considered in the Calculations

where s = 1 for adiabatic expansion, and s = (α + 2)/4 fora case with the heating rate ∝ t −α , which can be derived
from the second law of thermodynamics, T d(T 3 R 3 )/dt ∝ t −α
(Li & Paczyński 1998). Recent detailed studies of r-process
nucleosynthesis have suggested α = 1.2–1.3 (Metzger et al.
2010; Korobkin et al. 2012; Rosswog et al. 2014; Wanajo et al.
2014). Our results are not sensitive to s because dust-formation
temperature is not far from T0 .
The density of the ejecta ρ0 at t0 is estimated from thecondition that the diffusion time of photons ∼ρ0 R 2 κ/c iscomparable to the dynamical time ∼R/cβ for a given opacity
coefficient κ, which is achieved at around the luminosity peak.
The upper limit of the NIR flux at ∼20 days in the rest frame
suggests that the luminosity peaks at ∼10 days (Tanvir et al.
2013). The density scales as ρ = ρ0 (t/t0 )−3 and therefore,ρ ∼ 1.4 × 10−16



−1 

κ
β −2
10 cm2 g−1
0.2
−3

t
×
g cm−3 .
7 daysM ∼ 1.4 × 10


M

ΔΩ
4π



κ
10 cm2 g−1

−1 γ /104 K

δ

a0
(Å)

σ
(erg cm−2 )

Teq
(K)

C
Fe
Sr
Hf
Pt

8.640
4.842
1.456
7.390
6.777

18.97416.5577.067
16.22017.826

1.281
1.411
2.364
1.745
1.533

1400
1800
165
1510
1770

1800–2000
1060–1180
430–500
1630–1820
1440–1600

Notes. The Gibbs free energy for the formation of the condensate is approximated by Δg̊/kT = −γ /T + δ, where the numerical values γ and δ arederived by least-squares fittings of the thermodynamics data (Chase et al. 1985;
Arblaster 2005) in the temperature range of T = 200–2500 K. The radius of thecondensate per atom and the surface tension of the condensate are given as a0 and
σ , respectively (Elliott & Gleiser 1980; Nozawa et al. 2003). The equilibrium
temperatures Teq are presented for the density range of ni = 106 –108 cm−3 .
See Nozawa & Kozasa (2013) for the details of the dust formation calculations.

nucleosynthesis, respectively. Hf is taken as a substitution forlanthanoid elements.5
One of the conditions necessary for dust formation is that thetimescale of collisions between atoms τcoll = [π a02 ni v]−1 ismuch shorter than that of the expansion of the ejecta τexp =|(1/ρ)(dρ/dt)|−1 . Here, a0 ∼ 1Å, ni = ρi /mi , mi = Ai mH ,and Ai are the radius, number density, mass, and molecularweight of the element i, respectively. mH is the mass of ahydrogen atom. The mean thermal velocity is represented by
v = (2kB T /mi )1/2 with the Boltzmann constant kB . Then,
using Equations (2) and (3), the ratio τcoll /τexp is(3)   2 1
Ai mH 1/2 T − s − 2
τcoll
3Ai mH=τexp
T0
π a02 fi ρ0 t0 2kB T0−1 32 
Ai
ρ0 0.45fi−1
100
10−16 g cm−321
− s − 2T×.
2000 K

We examine the two cases for ejecta density. One case is
low-density ejecta with κ = 10 cm2 g−1 , which is the casewhere r-process elements are efficiently synthesized and are
responsible for the opacity of the gas (Kasen et al. 2013; Tanaka& Hotokezaka 2013). The other case is high-density ejecta with
κ = 0.1 cm2 g−1 , which corresponds to the opacity coefficientof Fe-rich Type Ia supernovae (e.g., Pinto & Eastman 2000),i.e., inefficient r-process nucleosynthesis.
The corresponding mass of the ejecta M = ΔΩR 3 ρ/3 is−2Grain Species(5)This ratio is sensitive to the temperature (∝ T −3.0 for α = 1.2),
and increases with time. A dust grain does not form if this ratio
is above unity. For instance, the ratio is ∼1 in the low-density
ejecta with fi ∼ 0.5 and Ai ∼ 200, which indicates that dust
grains of r-process elements are difficult to form.
We calculate dust formation by applying the formulation of
non-steady-state dust formation in Nozawa & Kozasa (2013)
with s = 0.8, i.e., α = 1.2 under T and ρ given in Section 2.
The results are summarized in Figure 1. In the low-density
ejecta Sr, Hf, and Pt never condense into dust grains even forfi = 1.0. Here, dust grains are defined as clusters containing
more than a hundred atoms. Fe grains also cannot be formed
even if fi = 1.0 because of its low condensation temperature(1000 K). Note that condensation temperature is lower thanthe equilibrium temperature because supersaturation is requiredfor dust formation. The formation of carbon grains is possible
as a result of the high condensation temperature (1800 K) andsmall molecular weight (see Equation (5)), i.e., large number
density, which achieves fcon = 0.08 and 0.5 for fi = 0.5 and
1.0, respectively. These carbon grains could be responsible for


β
, (4)
0.2

where ΔΩ is the solid angle within which the ejecta areblown off. Regarding dynamical ejecta, general relativistichydrodynamical simulations have indicated ΔΩ/4π ∼ 1 for
NS–NS mergers (Hotokezaka et al. 2013a), and ΔΩ/4π ∼ 0.1
for BH–NS mergers (Kyutoku et al. 2013).
3. DUST FORMATION
3.1. Dust Formation in the Ejecta
Dust can form below the equilibrium temperature at which
the partial pressure of an element i equals the vapor pressure of
the condensate which depends only on temperature and atomic
species. The partial gas pressure can be calculated from T
and ρi = fi ρ with the equation of state of ideal gas, wherefi is the mass fraction of the element i. This study focuses
on representative elements in Table 1 individually instead ofin a complicated composition to avoid complexity. Sr and
Pt are elements in the first and third peaks of the r-process

5

The data necessary for dust formation calculations are not available forlanthanoid elements. The second peak element of the r-process is Xe, but Xedust does not form easily because Xe is a noble gas.

2

The Astrophysical Journal Letters, 789:L6 (5pp), 2014 July 1

Takami, Nozawa, & Ioka

Figure 2. Condensation efficiency and average radius of newly formed carbon
grains as a function of the isotropic mass of carbon MC (4π/ΔΩ) (MC isthe carbon mass available for dust formation). The radius of carbon grains
with 100 atoms is also shown (dotted). The vertical dashed line marks theamount of carbon gas which is required to produce the dust emission spectrum(Md,C = 8 × 10−6 M ) in Figure 3 for ΔΩ = 4π .
(A color version of this figure is available in the online journal.)
Figure 1. Condensation efficiency, defined as the mass fraction of atoms locked
up in dust grains, of carbon, iron, strontium, hafnium, and platinum in the lowdensity (upper) and high-density (lower) cases. Note that the dust formation of
Hf and Pt in the high-density case is unlikely because low fi (10−2 ) is required
for r-process elements in GRB 130603B.

the opacity of ejecta if a significant amount of carbon exists. We
conclude that the dust grains of heavy (Ai  50) elements are
not expected to be formed in the low-density case. In particular,
the condensation of r-process elements (Ai  100) is extremely
difficult unless the inhomogeneity of ejecta is taken into account.
In the high-density ejecta (see Equation (3)), the necessary
condition for dust formation is relaxed. Carbon grains form att ∼ 7 days with fcon = 1.0 for fi = 0.5. Despite the highdensity, the low condensation temperature permits Fe grains
only below fcon = 2 × 10−3 and no Sr grains even for fi = 1.0.
Dust grains of Hf and Pt could form if fi is high enough.
However, for GRB 130603B, such a high fi is unlikely because asignificant amount of r-process elements leads to κ much larger
than 0.1 cm2 g−1 , which is far from the definition of the highdensity case (κ ∼ 0.1 cm2 g−1 ) and therefore is inconsistent withthe observation. Since Fe grains form much later than t0 = 7
days,6 we exclusively focus on carbon grains for GRB 130603B
in the next subsection.

Figure 3. Thermal emission spectrum of carbon grains with 1800 K (red) in theobserver frame. The black square is the observed NIR flux of GRB 130603B(Tanvir et al. 2013). For reference, a spectrum of the r-process model (blue;
Tanaka & Hotokezaka 2013, TH13) and a blackbody spectrum with T = 2000
K (green) are shown. The spectral shape of the dust emission is smoother thanthat of the r-process model. Note that the parameters of TH13 are not optimized
for GRB 130603B.
(A color version of this figure is available in the online journal.)

dust emission spectrum. The required mass of carbon grains is
Md,C ∼ 8 × 10−6 M with a dust temperature of 1800 K. Since
Md,C = fcon MC , the condensation efficiency for achieving thisdust mass is estimated as fcon = 2 × 10−3 (MC = 4 × 10−3 M ;see Figure 2) for isotropic ejecta, i.e., ΔΩ = 4π . For anisotropic
ejecta (ΔΩ < 4π ), a specific MC leads to fcon larger in the casesof smaller ΔΩ because of the higher ejecta density. Thus, asmaller amount of MC is sufficient to obtain a fixed value of Md,C
for a smaller ΔΩ. We can estimate fcon and MC to yield a given
Md,C = fcon MC by using the red line in Figure 2. For instance, inthe case of (4π/ΔΩ) = 10, fcon ∼ 2 × 10−2 , which is achieved
when the mass of carbon gas is MC ∼ 5 × 10−4 M . Note thatthe required mass of carbon gas is consistent with the mass ofejecta which is shown in recent simulations. We also note thatcarbon grains do not evaporate because the dust temperature islower than its evaporation (equilibrium) temperature.
The opacity coefficient of the carbon grains is κC ∼ 1.1 ×
104 cm2 g−1 at the J band (1.2 μm), which does not depend

3.2. Dust Model for Macronovae
Figure 2 shows the condensation efficiency and average radiusof carbon grains in the high-density ejecta (see Equation (3)) as afunction of the isotropic equivalent mass of carbon MC (4π/ΔΩ),
where MC is the mass of carbon available for dust formation.
The density of ejecta is calculated as the isotropic equivalentmass divided by 4π R 3 /3. The condensation efficiency is unity
above MC (4π/ΔΩ) ∼ 10−2 , below which it decreases rapidly.
Once dust grains are formed in the ejecta, they absorb
emission from the ejecta and emit photons with energies
corresponding to their temperature. Assuming that dust emission
is optically thin, we can choose the mass and temperature of dust
so that its thermal emission explains the NIR emission of GRB
130603B. Figure 3 demonstrates one of the examples of the
6

Fe grains could form at an earlier time in non-uniform ejecta, e.g., at thehead of the ejecta where gas is rapidly cooled.

3

The Astrophysical Journal Letters, 789:L6 (5pp), 2014 July 1

21

Takami, Nozawa, & Ioka

We inferred the temperature of ejecta from the observational
result as T0 ∼ 2000 K. A heating source may be the radioactive
decay products of r-process elements in the r-process model. In
r-process nucleosynthesis inefficient ejecta one possibility is theradioactive decay of heavy, but not r-process, elements (Barnes& Kasen 2013). Radioactive nuclei with the lifetime less than
∼10 days release a significant fraction of radioactive energies
and achieve T ∼ 2000 K at ∼7 days under a reasonable choiceof ejecta mass. Shock heating also may be possible.
We should keep in mind that the discussions in this Letter are
based on the observational result of GRB 130603B because
this is the only existing sample. For instance, if the ejecta
temperature is lower and density is much higher in anothermacronova, dust grains of r-process elements could be formed.
Our results have shown that newly formed grains are relatively
small, consisting of ∼100 up to ∼105 atoms. We adopted
the theory of Mie scattering in calculating the absorption
coefficients of dust. However, they might deviate from theprediction of the theory for the dust only containing order-ofhundreds atoms.
We have considered homogeneous ejecta for simplicity. In
reality, ejecta may be inhomogeneous, and dust may be formed
in dense clumps, as in supernovae (e.g., Kotak et al. 2009;
Indebetouw et al. 2014). Larger dust grains may be formed
in higher density clumps, and then opacity by dust can bechanged by reflecting the spatial distribution of dust. Moreover,the consideration of the radial profile of ejecta may modify adust formation history. Such effects are interesting subjects tobe studied in the future.
The dust model for NIR macronovae should be tested observationally. One method of testing this is through the confirmationof a featureless spectrum. As shown in Figure 3, a dust emission spectrum is featureless compared to a broad spectrum inthe r-process model. A spectrum in the dust model also deviates from a blackbody spectrum at long wavelengths. Anotherway of testing is through multi-wavelength observations of light
curves from early epochs (see Figure 4). Without the opacityof r-process elements, a macronova is bright and blue in an
early phase. It becomes red later through the emission of newly
formed dust. Early optical emission was explored for a few short
GRBs (e.g., GRB 050509B; Hjorth et al. 2005). Although theflux limit is strong for these GRBs, continuous searches for early
emission are important because the properties of ejecta in NSB
mergers may not be universal, e.g., depending on progenitors(NS–NS/BH–NS). In both cases, quick follow-up observations
are important to understand the origin of NIR macronovae aswell as the nucleosynthesis in the mergers of compact stellar
objects.

F606W
F160W

22
AB magnitude

23
24
25
Macronova
before Dust
Formation

26
27

Dust

28
29
10

4

5

6

10
10
Time since GRB 130603B (s)Figure 4. Schematic light curves for the interpretation of GRB 130603B by thedust model. The data points and fits by a GRB afterglow model (dashed lines)
are from Tanvir et al. (2013).
(A color version of this figure is available in the online journal.)

on their radius as long as the grain radius is much smaller
than the wavelength. At 7 days in the rest frame, the absorption probability is above unity at wavelengths shorter than the
J band under the parameter choice: (3Md,C /ΔΩR 3 )κC Rβ ∼0.7(4π/ΔΩ)(λ/1.2 μm)−1.2 . The absorption (emission) coefficients are proportional to λ−1.2 (Zubko et al. 1996). Thus, thedust grains absorb macronova emission and re-emit radiation at
NIR wavelengths.
Compared to the r-process model, which predicts a rather
broad-line spectrum, the dust model provides a spectrum witheven fewer features. The spectrum of dust emission also deviatesfrom a blackbody spectrum at wavelengths of 5 μm because of
the λ-dependence of the emission coefficient. Thus, a spectrumof the dust model can be observationally distinguished fromboth the r-process model and a pure blackbody spectrum.
Based on the discussion above, we can propose an alternativemodel for the NIR brightening of GRB 130603B, and macronovae in general, which is schematically drawn in Figure 4. First,
a macronova that is not powered by r-process elements happens. The low line opacity coefficient, e.g., κ ∼ 0.1 cm2 s−1 ,makes this event bright in the blue band on a timescale of afew days, as in the original work (Li & Paczyński 1998). Then,
when the temperature of the ejecta decreases to ∼2000 K, dust
formation begins and the ejecta become opaque again by dust.
The high opacity allows the macronova emission to heat dust
grains, which emit absorbed photons at NIR wavelengths. In
other words, the observed NIR macronova can be the dust emission. The dust model has a featureless spectrum and an earlymacronova in the blue band, compared to the r-process model
which has a broad-line spectrum and no early blue emission.

We thank J. Hjorth and N. R. Tanvir for useful comments, M.
Tanaka for providing us with a macronova spectrum (Figure 3),
and K. Hotokezaka, T. Nakamura, Y. Sekiguchi, and M. Shibata
for discussions. T. Nakamura had also investigated dust formation in macronova independently of us. This work is supported
by KAKENHI 24·9375 (H.T.), 22684004, 23224004, 26400223(T.N.), 24000004, 22244030, 24103006, and 26287051 (K.I.),and by the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan.

4. DISCUSSION AND SUMMARY
We have investigated dust formation in macronovae basedon the temperature and density estimated from GRB 130603B.
We have shown that dust from r-process elements hardly forms
even if these elements are abundantly produced. On the other
hand, dust of light elements, such as carbon, can be formed. We
have also suggested that the NIR macronova of GRB 130603B
can be explained by the emission of light-element dust such ascarbon grains, as an alternative to the r-process model.

REFERENCES
Abadie, J., & LIGO Collaboration., 2010, NIMPA, 624, 223
Accadia, T., Acernese, F., Antonucci, F., et al. 2011, CQGra, 28, 114002
Arblaster, J. W. 2005, Platinum. Metals. Rev., 49, 1414

The Astrophysical Journal Letters, 789:L6 (5pp), 2014 July 1

Takami, Nozawa, & Ioka
Metzger, B. D., & Fernández, R. 2014, arXiv:1402.4803
Metzger, B. D., Martı́nez-Pinedo, G., Darbha, S., et al. 2010, MNRAS,
406, 2650
Nakar, E., & Piran, T. 2011, Natur, 478, 82
Nozawa, T., & Kozasa, T. 2013, ApJ, 776, 24
Nozawa, T., Kozasa, T., Umeda, H., Maeda, K., & Nomoto, K. 2003, ApJ,
598, 785
Pinto, P. A., & Eastman, R. G. 2000, ApJ, 530, 757
Piran, T., Nakar, E., & Rosswog, S. 2013, MNRAS, 430, 2121
Rosswog, S., Korobkin, O., Arcones, A., & Thielemann, F.-K. 2014, MNRAS,
439, 744
Rosswog, S., Liebendörfer, M., Thielemann, F.-K., et al. 1999, A&A, 341, 499
Rosswog, S., Ramirez-Ruiz, E., & Davies, M. B. 2003, MNRAS, 345, 1077
Ruffert, M., & Janka, H.-T. 2001, A&A, 380, 544
Ruffert, M., Janka, H.-T., Takahashi, K., & Schaefer, G. 1997, A&A, 319, 122
Shibata, M., Suwa, Y., Kiuchi, K., & Ioka, K. 2011, ApJL, 734, L36
Surman, R., Caballero, O. L., McLaughlin, G. C., Just, O., & Janka, H.-T.
2014, JPhG, 41, 044006
Takami, H., Kyutoku, K., & Ioka, K. 2014, PhRvD, 89, 063006
Tanaka, M., & Hotokezaka, K. 2013, ApJ, 775, 113
Tanaka, M., Hotokezaka, K., Kyutoku, K., et al. 2014, ApJ, 780, 31
Tanvir, N. R., Levan, A. J., Fruchter, A. S., et al. 2013, Natur, 500, 547
Wanajo, S., Sekiguchi, Y., Nishimura, N., et al. 2014, arXiv:1402.7317
Zubko, V. G., Mennella, V., Colangeli, L., & Bussoletti, E. 1996, MNRAS,
282, 1321

Barnes, J., & Kasen, D. 2013, ApJ, 775, 18
Bauswein, A., Goriely, S., & Janka, H.-T. 2013, ApJ, 773, 78
Berger, E., Fong, W., & Chornock, R. 2013, ApJL, 774, L23
Chase, M. W., Jr., Davies, C. A., Downey, J. R., Jr., et al. 1985, JPCRD, 14, 1
Dessart, L., Ott, C. D., Burrows, A., Rosswog, S., & Livne, E. 2009, ApJ,
690, 1681
Elliott, J. F., & Gleiser, M. 1980, Thermochemistry for Steelmaking, Vol. 1(Reading, MA: Addison-Wesley)
Fernández, R., & Metzger, B. D. 2013, MNRAS, 435, 502
Goriely, S., Bauswein, A., & Janka, H.-T. 2011, ApJL, 738, L32
Hjorth, J., Sollerman, J., Gorosabel, J., et al. 2005, ApJL, 630, L117
Hotokezaka, K., Kiuchi, K., Kyutoku, K., et al. 2013a, PhRvD, 87, 024001
Hotokezaka, K., Kyutoku, K., Tanaka, M., et al. 2013b, ApJL, 778, L16
Indebetouw, R., Matsuura, M., Dwek, E., et al. 2014, ApJL, 782, L2
Jin, Z.-P., Xu, D., Fan, Y.-Z., Wu, X.-F., & Wei, D.-M. 2013, ApJL, 775, L19
Kasen, D., Badnell, N. R., & Barnes, J. 2013, ApJ, 774, 25
Korobkin, O., Rosswog, S., Arcones, A., & Winteler, C. 2012, MNRAS,
426, 1940
Kotak, R., Meikle, W. P. S., Farrah, D., et al. 2009, ApJ, 704, 306
Kulkarni, S. R. 2005, arXiv:astro-ph/0510256
Kuroda, K., & LCGT Collaboration., 2010, CQGra, 27, 084004
Kyutoku, K., Ioka, K., & Shibata, M. 2013, PhRvD, 88, 041503
Kyutoku, K., Ioka, K., & Shibata, M. 2014, MNRAS, 437, L6
Li, L.-X., & Paczyński, B. 1998, ApJL, 507, L59
LIGO Scientific Collaboration, et al. 2013, arXiv:1304.0670

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