Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Implications of Recent Observations of the Inner Knot in the Crab
  Nebula   Recent observations of the Crab Nebula (Rudy et al 2015) have maintained its
reputation for high energy astrophysical enlightenment and its use as a testbed
for theories of the behaviour of magnetized, relativistic plasma. In
particular, new observations of the inner knot located 0.65" SE from the pulsar
confirm that it is compact, elongated transversely to the symmetry axis and
curved concave towards the pulsar. 60 percent polarization has been measured
along the symmetry axis (Moran et al 2013). The knot does not appear to be
involved in the gamma ray flares. The new observations both reinforce the
interpretation of the knot as dissipation of the pulsar wind at a strong shock
and challenge the details of existing models of this process. In particular, it
is argued that the compactness, high polarization and curvature are difficult
to reconcile with simple relativistic shock models. Alternative possibilities
include deflection of the outflow ahead of the shock and spatial variation in
which the knot is interpreted as a caustic. Some future observations are
proposed and new theoretical investigations are suggested.

37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys