137 research outputs found
The XMM-Newton view of the relativistic spectral features in AXJ0447-0627
The XMM-Newton observation of the optically Type 1 AGN AXJ0447-0627 (z=0.214)
unambiguously reveals a complex, bright and prominent set of lines in the 4-8
keV rest frame energy range. Although, from a phenomenological point of view,
the observed properties can be described by a simple power law model plus 5
narrow Gaussian lines (at rest frame energies of nearly 4.49, 5.55, 6.39, 7.02
and 7.85 keV), we find that a model comprising a power law (Gamma of the order
of 2.2), a reflected relativistic continuum, a narrow Fe I Kalpha line from
neutral material as well as a broad Fe Kalpha relativistic line from a ionized
accretion disk represents a good physical description of the data. The ''double
horned'' profile of the relativistic line implies an inclination of the
accretion disk of the order of 45 degree, and an origin in a narrow region of
the disk, from R_in of the order of 19 GM/c^2 to R_out of the order of 30
GM/c^2. The narrow Fe I Kalpha line from neutral material is probably produced
far from the central black hole, most likely in the putative molecular torus.
Although some of these properties have been already found in other Type 1 AGN
and discussed in the literature, at odd with the objects reported so far we
measure high equivalent widths (EWs) of the observed lines: nearly 1.4 keV for
the ``double horned'' relativistic line and nearly 0.4 keV for the narrow line.Comment: 16 pages, 3 figures, Latex manuscript; accepted for publication in
Ap
Exploring the X-ray Sky with the XMM-Newton Bright Serendipitous Survey
ABRIDGED. We present "The XMM-Newton Bright Serendipitous Survey", two
flux-limited samples with flux limit fx ~7E-14 cgs in the 0.5-4.5 keV (BSS) and
4.5-7.5 keV (HBSS) energy band, respectively. After discussing the survey
strategy, we present the basic data on a complete sample of 400 X-ray sources
derived from the analysis of 237 XMM-Newton fields. The survey covers an area
of 28.10 (25.17 for the HBSS) sq. deg. Up to now ~71% (~90%) of the sources
have been spectroscopically identified making the BSS (HBSS) the sample with
the highest number of identified XMM-Newton sources published so far. We find
that: a) the optical counterpart in the majority (~90%) of cases has a
magnitude brighter than the POSS II limit; b) the majority of the objects
identified so far are broad line AGN. No obvious trend of the source spectra
(as deduced from the Hardness Ratios analysis) as a function of the count rate
is seen and the average spectra of the "extragalactic" population corresponds
to an X-ray energy spectral index of ~0.8 (~0.64) for the BSS (HBSS) sample.
About 13% (40%) of the sources are described by an energy spectral index
flatter than that of the CXB. We measure a surface density of optically type 1
and type 2 AGN of 1.63+/-0.25 deg-2 and 0.83+/-0.18$ deg-2, respectively;
optically type 2 AGN represent 34+/-9% of the total AGN population. Finally, we
find a clear separation, in the hardness ratio diagram and in the (hardness
ratio) vs. (X-ray to optical flux ratio) diagram, between "coronal emitting"
stars and extragalactic sources.Comment: 42 pages, 7 figures, 8 Tables, Accepted for publication in A&
On the cosmological evolution of BL Lacs
We study the cosmological evolution of BL Lac objects by applying the Ve/Va
analysis to a new sample of 55 objects presented for the first time in this
paper. This sample has been selected from the 239 sources with the brightest
X-ray flux (>4X10^-13 erg s^-1 cm^-2) and relatively bright optical counterpart
(B<20.5) among the ~1600 objects included in the REX survey. The uniform
distribution of the Ve/Va values found in the sample suggests that BL Lac
objects are not affected by a strong cosmological evolution in contrast with
the behavior observed in the emission line AGNs. The Ve/Va analysis applied to
the subsample of the High energy peaked BL Lacs (HBL) does not reveal a
significant departure from a uniform distribution. This result suggests either
that the cosmological evolution is less extreme than that previously found in
other samples or that it is carried out only by a minority of objects, namely
by the most extreme HBLs.Comment: Accepted for publication in Part 1 of The Astrophysical Journa
XMM-Newton observations expose AGN in apparently normal galaxies
We have performed a detailed analysis of 3 optically normal galaxies
extracted from the XMM Bright Serendipitous Source Sample. Thanks to the good
statistics of the XMM-Newton data, we have unveiled the presence of an AGN in
all of them. In particular, we detect both X-ray obscured (N_H>10^{22} cm^{-2})
and unobscured (N_H<10^{22} cm^{-2}) AGN with intrinsic 2--10 keV luminosities
in the range between 10^{42} -- 10^{43} erg s^{-1}. We find that the X-ray and
optical properties of the sources discussed here could be explained assuming a
standard AGN hosted by galaxies with magnitudes M_R<M^*, taking properly into
account the absorption associated with the AGN, the optical faintness of the
nuclear emission with respect to the host galaxy, and the inadequate set--up
and atmospheric conditions during the optical spectroscopic observations. Our
new spectroscopic observations have revealed the expected AGN features also in
the optical band. These results clearly show that optical spectroscopy
sometimes can be inefficient in revealing the presence of an AGN, which instead
is clearly found from an X-ray spectroscopic investigation. This remarks the
importance of being careful in proposing the identification of X-ray sources
(especially at faint fluxes) when only low quality optical spectra are in hand.
This is particularly important for faint surveys (such as those with XMM-Newton
and Chandra), in which optically dull but X-ray active objects are being found
in sizeable numbers.Comment: Accepted for publication on A&A; 11 pages, 8 figure
A sample of X-ray emitting normal galaxies from the BMW -- HRI Catalogue
We have obtained a sample of 143 normal galaxies with X-ray luminosity in the
range erg s from the cross-correlation of the ROSAT
HRI Brera Multi-scale Wavelet (BMW -- HRI) Catalogue with the Lyon-Meudon
Extragalactic Database (LEDA). We find that the average X-ray properties of
this sample are in good agreement with those of other samples of galaxies in
the literature. We have selected a complete flux limited serendipitous sample
of 32 galaxies from which we have derived the logN-logS distribution of normal
galaxies in the flux range erg cm s.
The resulting distribution is consistent with the euclidean -1.5 slope.
Comparisons with other samples, such as the Extended Medium Sensitivity Survey,
the ROSAT All Sky Survey, the XMM - Newton/2dF survey and the Chandra Deep
Field Survey indicate that the logN-logS distribution of normal galaxies is
consistent with an euclidean slope over a flux range of about 6 decades.Comment: Accepted for publication in A&A. 19 pages, 7 figures. Full resolution
version of Figure 2 is available at http://www.brera.mi.astro.it/~tajer
Cluster Evolution in the ROSAT North Ecliptic Pole Survey
The deepest region of the ROSAT All-Sky Survey, at the North Ecliptic Pole,
has been studied to produce a complete and unbiased X-ray selected sample of
clusters of galaxies. This sample is used to investigate the nature of cluster
evolution and explore potential implications for large-scale structure models.
The survey is 99.6% optically identified. Spectroscopic redshifts have been
measured for all the extragalactic identifications. In this Letter, first
results on cluster evolution are presented based on a comparison between the
number of the observed clusters in the North Ecliptic Pole survey and the
number of expected clusters assuming no-evolution models. At z>0.3 there is a
deficit of clusters with respect to the local universe which is significant at
> 4.7sigma. The evolution appears to commence at L_{0.5-2.0} > 1.8x10^{44} erg
s^{-1} in our data. The negative evolution goes in the same direction as the
original EMSS result, the results from the 160 deg^{2} survey by Vikhlinin et
al. (1998) and the recent results from the RDCS (Rosati et al. 2000). At lower
redshifts there is no evidence for evolution, a result in agreement with these
and other cluster surveys.Comment: 17 pages, 3 figures. Accepted for publication in ApJ Letter
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