Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Keck and ESO-VLT View of the Symmetry of the Ejecta of the XRF/SN 2006aj   Nebular-phase spectra of SN 2006aj, which was discovered in coincidence with
X-ray flash 060218, were obtained with Keck in 2006 July and the Very Large
Telescope in 2006 September. At the latter epoch spectropolarimetry was also
attempted, yielding an upper limit of ~ 2% for the polarization. The spectra
show strong emission lines of [OI] and MgI], as expected from a Type Ic
supernova, but weak CaII lines. The [FeII] lines that were strong in the
spectra of SN 1998bw are much weaker in SN 2006aj, consistent with the lower
luminosity of this SN. The outer velocity of the line-emitting ejecta is ~ 8000
km/s in July and ~ 7400 km/s in September, consistent with the relatively low
kinetic energy of expansion of SN 2006aj. All emission lines have similar
width, and the profiles are symmetric, indicating that no major asymmetries are
present in the ejecta at the velocities sampled by the nebular lines (v < 8000
km/s), except perhaps in the innermost part. The spectra were modelled with a
non-LTE code. The mass of 56Ni required to power the emission spectrum is ~
0.20 Msun, in excellent agreement with the results of early light curve
modelling. The oxygen mass is ~ 1.5 Msun, again much less than in SN 1998bw but
larger by ~ 0.7 Msun than the value derived from the early-time modelling. The
total ejected mass is ~ 2 Msun below 8000 km/s. This confirms that SN 2006aj
was only slightly more massive and energetic than the prototypical Type Ic SN
1994I, but also indicates the presence of a dense inner core, containing ~ 1
Msun of mostly oxygen and carbon. The presence of such a core is inferred for
all broad-lined SNe Ic. This core may have the form of an equatorial
oxygen-dominated region, but it is too deep to affect the early light curve and
too small to affect the late polarization spectrum.

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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: math
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The categories of this paper are: nlin
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: chem-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
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The categories of this paper are: mtrl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an