Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Short Hard X-ray Flare from the Blazar NRAO 530 Observed by INTEGRAL   We report about a short flare from the blazar NRAO 530 occurred on 17
February 2004 and detected serendipitously by the IBIS/ISGRI detector on board
INTEGRAL. In the 20-40 keV energy range, the source, that is otherwise below
the detection limit, is detected at a level of ~2 x 10^-10 erg cm^-2 s^-1
during a time interval of less than 2000 s, which is about a factor 2 above the
detection threshold. At other wavelengths, only nearly-simultaneous radio data
are available (1 observation at 2 cm on 11 February 2004), indicating a
moderate increase of the polarization. This appears to be the shortest time
variability episode ever detected in a high luminosity blazar at hard X-rays,
unless the blazar is contaminated by the presence of an unknown unresolved
rapidly varying source.

20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
7
The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an