16 research outputs found
The X-ray spectral properties of X-ray selected AGN : ROSAT spectra of EMSS AGN
Using a sample of 63 AGNs extracted from the Extended Medium
Sensitivity Survey (EMSS), we study the X-ray spectral properties of X-ray
selected AGN in the 0.12.4 keV ROSAT band. These objects are all the EMSS
AGN detected with more than 300 net counts in ROSAT PSPC images available from
the public archive (as of May 31, 1995). A Maximum-Likelihood analysis is used
to find the mean power-law spectral index and the intrinsic
dispersion $\sigma_p$. We find =1.42 with =0.44. This
value is significantly steeper (0.4) than the mean
/IPC spectral index obtained applying the ML analysis on the whole
sample of EMSS AGN. This result shows that the soft excess already noted in
optically selected AGN is present also in X-ray selected AGN. The relatively
high value obtained for the intrinsic dispersion confirms that in the soft band
AGN are characterized by a variety of spectral indices and the increase with
respect to results obtained from the analysis of Einstein data (0.16) suggests a further broadening of the spectral index
distribution as one moves to softer energies. A comparison between the mean
spectral index of Radio-quiet and Radio-loud subsamples shows that the mean
index of the RL sample is flatter than that of RQ, both in the IPC (0.3) and in the PSPC (0.4) data. This suggests
that the additional X-ray component in RL AGN dominates the X-ray emission of
RL AGN over almost two decades of energy (0.110 keV).Comment: 8 pages LaTex file; mn.sty macro (enclosed), 5 LaTex Tables, 12
Postscript figures; accepted for publication in MNRA
A Medium Survey of the Hard X-Ray Sky with ASCA. II.: The Source's Broad Band X-Ray Spectral Properties
A complete sample of 60 serendipitous hard X-ray sources with flux in the
range \ecs to \ecs (2 - 10
keV), detected in 87 ASCA GIS2 images, was recently presented in literature.
Using this sample it was possible to extend the description of the 2-10 keV
LogN(>S)-LogS down to a flux limit of \ecs (the
faintest detectable flux), resolving about a quarter of the Cosmic X-ray
Background. In this paper we have combined the ASCA GIS2 and GIS3 data of these
sources to investigate their X-ray spectral properties using the "hardness"
ratios and the "stacked" spectra method. Because of the sample statistical
representativeness, the results presented here, that refer to the faintest hard
X-ray sources that can be studied with the current instrumentation, are
relevant to the understanding of the CXB and of the AGN unification scheme.Comment: 28 pages plus 6 figures, LaTex manuscript, Accepted for publication
in the Astrophysical Journal, Figure 5 can retrieved via anonymous ftp at
ftp://ftp.brera.mi.astro.it/pub/ASCA/paper2/fig5.ps.g