Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A new population of soft X-ray weak quasars   Quasars selected in optical surveys by means of their blue or UV excess are
known to be strong emitters in the X-rays, except for Broad Absorption Line
(BAL) objects. In this paper we study the X-ray emission of quasars selected
through their emission line spectrum rather than their blue excess. X-ray data
are obtained by cross-correlating two optical samples (the Hamburg Survey
Catalogue and the Palomar Transit Catalogue) with the WGA catalogue of ROSAT
observations. We find that a significant fraction of objects are strongly
underluminous in the X-rays. We discuss the physical nature of these sources
and we propose an interpretation for their optical and X-ray properties based
on a dust-poor and gas-rich absorber. Our results suggest the existence of a
population of AGNs having a type 1 optical spectrum and a type 2 X-ray emission

9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
23
The categories of this paper are: solv-int