Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The discovery of X-ray emission from the protostellar jet L1551 IRS5 (HH
  154)   We have for the first time detected X-ray emission associated with a
protostellar jet, on the jet emanating from the L1551 IRS5 protostar. The IRS5
protostar is hidden behind a very large absorbing column density, making the
direct observation of the jet's emission possible. The observed X-ray emission
is likely associated with the shock ``working surface'', i.e. the interface
between the jet and the circumstellar medium. The X-ray luminosity emanating
from the jet is moderate, at $L_{\rm X} \simeq 3 \times 10^{29}$ erg/s, a
significant fraction of the luminosity normally associated with the coronal
emission from young stars. The spectrum of the X-ray emission is compatible
with thermal emission from a hot plasma, with a temperature of $\simeq 0.5$ MK,
fully in line with the temperature expected (on the basis of the jet's
velocity) for the shock front produced by the jet hitting the circumstellar
medium.

30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex