Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: The X-ray spectrum of the cooling-flow quasar H1821+643 : A massive
  black hole feeding off the intracluster medium
23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat