Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Strong Merger Shock in Abell 665   Deep (103 ks) \chandra\ observations of Abell 665 have revealed rich
structures in this merging galaxy cluster, including a strong shock and two
cold fronts. The newly discovered shock has a Mach number of $M$ = 3.0 $\pm$
0.6, propagating in front of a cold disrupted cloud. This makes Abell~665 the
second cluster where a strong merger shock of $M \approx$ 3 has been detected,
after the Bullet cluster. The shock velocity from jump conditions is consistent
with (2.7 $\pm$ 0.7) $\times$ 10$^3$ km sec$^{-1}$. The new data also reveal a
prominent southern cold front, with potentially heated gas ahead of it. Abell
665 also hosts a giant radio halo. There is a hint of diffuse radio emission
extending to the shock at the north, which needs to be examined with better
radio data. This new strong shock provides a great opportunity to study the
re-acceleration model with the X-ray and radio data combined.

2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: nlin
26
The categories of this paper are: bayes-an
36
The categories of this paper are: cmp-lg
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The categories of this paper are: adap-org
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The categories of this paper are: comp-gas