Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measuring nickel masses in Type Ia supernovae using cobalt emission in
  nebular phase spectra   The light curves of Type Ia supernovae (SNe Ia) are powered by the
radioactive decay of $^{56}$Ni to $^{56}$Co at early times, and the decay of
$^{56}$Co to $^{56}$Fe from ~60 days after explosion. We examine the evolution
of the [Co III] 5892 A emission complex during the nebular phase for SNe Ia
with multiple nebular spectra and show that the line flux follows the square of
the mass of $^{56}$Co as a function of time. This result indicates both
efficient local energy deposition from positrons produced in $^{56}$Co decay,
and long-term stability of the ionization state of the nebula. We compile 77
nebular spectra of 25 SN Ia from the literature and present 17 new nebular
spectra of 7 SNe Ia, including SN2014J. From these we measure the flux in the
[Co III] 5892 A line and remove its well-behaved time dependence to infer the
initial mass of $^{56}$Ni ($M_{Ni}$) produced in the explosion. We then examine
$^{56}$Ni yields for different SN Ia ejected masses ($M_{ej}$ - calculated
using the relation between light curve width and ejected mass) and find the
$^{56}$Ni masses of SNe Ia fall into two regimes: for narrow light curves (low
stretch s~0.7-0.9), $M_{Ni}$ is clustered near $M_{Ni}$ ~ 0.4$M_\odot$ and
shows a shallow increase as $M_{ej}$ increases from ~1-1.4$M_\odot$; at high
stretch, $M_{ej}$ clusters at the Chandrasekhar mass (1.4$M_\odot$) while
$M_{Ni}$ spans a broad range from 0.6-1.2$M_\odot$. This could constitute
evidence for two distinct SN Ia explosion mechanisms.

13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
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The categories of this paper are: bayes-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph