Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Zooming in on a sleeping giant: milliarcsecond HSA imaging of the black
  hole binary V404 Cyg in quiescence   Observations of the black hole X-ray binary V404 Cyg with the very long
baseline interferometer HSA (the High Sensitivity Array) have detected the
source at a frequency of 8.4 GHz, providing a source position accurate to 0.3
mas relative to the calibrator source. The observations put an upper limit of
1.3 mas on the source size (5.2 AU at 4 kpc) and a lower limit of 7 x 10^6 K on
its brightness temperature during the normal quiescent state, implying that the
radio emission must be non-thermal, most probably synchrotron radiation,
possibly from a jet. The radio lightcurves show a short flare, with a rise time
of about 30 min, confirming that the source remains active in the quiescent
state.

31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
17
The categories of this paper are: q-fin
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics