559 research outputs found
X-ray Line Emitting Objects in XMM-Newton Observations: the Tip of the Iceberg
We present preliminary results from a novel search for X-ray Line Emitting
Objects (XLEOs) in XMM-Newton images. Three sources have been detected in a
test-run analysis of 13 XMM-Newton observations. The three objects found are
most likely extremely absorbed AGN characterized by a column density
NH~10^24cm^-2. Their redshift has been directly determined from the X-ray data,
by interpreting the detected emission line as the 6.4 keV Fe line. The measured
equivalent width of the X-ray line is, in all three cases, several keV. This
pilot study demonstrates the success of our search method and implies that a
large sample of XLEOs can be obtained from the public XMM-Newton data archive.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter
A deep Chandra observation of the interacting star-forming galaxy Arp 299
We present results from a 90 ks Chandra ACIS-S observation of the X-ray
luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25
discrete X-ray sources with luminosities above 4.0x10^38 erg s^-1 covering the
entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray
spectra of the non-nuclear discrete sources identified in Arp 299, and their
association with young, actively star-forming region of Arp 299 we identify
them as HMXBs. We find in total 20 off-nuclear sources with luminosities above
the ULX limit, 14 of which are point-like sources. Furthermore we observe a
marginally significant deficit in the number of ULXs, with respect to the
number expected from scaling relations of X-ray binaries with the star
formation rate (SFR). Although the high metalicity of the galaxy could result
in lower ULX numbers, the good agreement between the observed total X-ray
luminosity of ULXs, and that expected from the relevant scaling relation
indicates that this deficit could be the result of confusion effects. The
integrated spectrum of the galaxy shows the presence of a hot gaseous component
with kT = 0.72+-0.03 keV, contributing 20% of the soft (0.1-2.0 keV) unabsorbed
luminosity of the galaxy. A plume of soft X-ray emission in the west of the
galaxy indicates a large scale outflow. We find that the AGN in NGC 3690
contributes only 22% of the observed broad-band X-ray luminosity of Arp 299.Comment: 20 pages, 14 figures, 9 tables. Accepted for publication in MNRA
GALEX measurements of the Big Blue Bump as a tool to study bolometric corrections in AGNs
Active Galactic Nuclei emit over the entire electromagnetic spectrum with the
peak of the accretion disk emission in the far-UV, a wavelength range
historically difficult to investigate. We use here the GALEX (Galaxy Evolution
Explorer) Near-UV and Far-UV measurements (complemented with optical data from
Sloan Digital Sky Survey (SDSS) and XMM-Newton X-ray spectra) of a sample of 83
X-ray selected type 1 AGN extracted from the XMM-Newton Bright Serendipitous
Survey to study their spectral energy distribution (SED) in the optical, Near
and Far-UV and X-ray energy bands. We have constrained the luminosity of the
accretion disk emission component and calculated the hard X-ray bolometric
corrections for a significant sample of AGN spanning a large range in
properties (z, L(x)).Comment: 2 pages, 2 figures, To appear in refereed Proceedings of "X-ray
Astronomy 2009: Present Status, Multi-Wavelength Approach and Future
Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri,
M. Cappi, and L. Angelin
The role of relativistic jets in the heaviest and most active supermassive black holes at high redshift
In powerful radio-quiet active galactic nuclei (AGN), black holes heavier
than one billion solar masses form at a redshift ~1.5-2. Supermassive black
holes in jetted radio-loud AGN seems to form earlier, at a redshift close to 4.
The ratio of active radio-loud to radio-quiet AGN hosting heavy black holes is
therefore a rather a strong function of redshift. We report on some recent
evidence supporting this conclusion, gathered from the Burst Alert Telescope
(BAT, onboard Swift) and by the Large Area Telescope (LAT, onboard Fermi). We
suggest that the more frequent occurrence of relativistic jets in the most
massive black holes at high redshifts, compared to later times, could be due to
the average black hole spin being greater in the distant past, or else to the
jet helping a fast accretion rate (or some combination of the two scenarios).
We emphasize that the large total accretion efficiency of rapidly spinning
black holes inhibits a fast growth, unless a large fraction of the available
gravitational energy of the accreted mass is not converted into radiation, but
used to form and maintain a powerful jet.Comment: 6 pages, 3 figures, accepted for publication in MNRAS, main journa
A FIRST DETERMINATION OF THE SURFACE DENSITY OF GALAXY CLUSTERS AT VERY LOW X--RAY FLUXES
We present the first results of a serendipitous search for clusters of
galaxies in deep ROSAT-PSPC pointed observations at high galactic latitude. The
survey is being carried out using a Wavelet based Detection Algorithm which is
not biased against extended, low surface brightness sources. A new
flux--diameter limited sample of 10 cluster candidates has been created from
surveyed area. Preliminary CCD observations have revealed
that a large fraction of these candidates correspond to a visible enhancement
in the galaxy surface density, and several others have been identified from
other surveys. We believe these sources to be either low--moderate redshift
groups or intermediate to high redshift clusters. We show X-ray and optical
images of some of the clusters identified to date. We present, for the first
time, the derived number density of the galaxy clusters to a flux limit of (0.5--2.0 keV). This extends the -- of previous cluster surveys by more than one decade in flux.
Results are compared to theoretical predictions for cluster number counts.Comment: uuencoded compressed Postscript, 7 pages including 4 figures.
Accepted for publication in Ap. J. Letters
The REX survey: a search for Radio Emitting X-ray sources
We present the scientific goals, the strategy and the first results of the
REX project, an effort aimed at creating a sizable and statistically complete
sample of Radio Emitting X-ray sources (REX) using the available data from a
VLA survey and the ROSAT PSPC archive. Through a positional cross-correlation
of the two data sets we have derived a sample of about 1600 REX. Among the 393
REX identified so far a high fraction is represented by AGNs, typically radio
loud QSOs and BL Lacs. The remaining sources are galaxies, typically radio
galaxies isolated or in cluster. Thanks to the low flux limits in the radio and
in the X-ray band and the large area of sky covered by the survey, we intend to
derive a new complete and unbiased sample of BL Lacs which will contain both
``RBL'' and ``XBL'' type objects. In this way, the apparent dichotomy resulting
from the current samples of BL Lacs will be directly analyzed in a unique
sample. Moreover, the high number of BL Lacs expected in the REX sample (about
200) will allow an accurate estimate of their statistical properties. To date,
we have discovered 15 new BL Lacs and 11 BL Lac candidates with optical
properties intermediate between those of a typical elliptical galaxy and those
of a typical BL Lac object. These objects could harbour weak sources of
non-thermal continuum in their nuclei and, if confirmed, they could represent
the faint tail of the BL Lac population. The existence of such ``weak'' BL Lacs
is matter of discussion in recent literature and could lead to a re-assessment
of the defining criteria of a BL Lac and, consequently, to a revision of their
cosmological and statistical properties.Comment: 30 pages, 13 figures, accepted for publication to Ap
Emission Line AGNs from the REX survey: Results from optical spectroscopy
We present 71 Emission Line objects selected from the REX survey. Except for
3 of them, for which the presence of an active nucleus is dubious, all these
sources are Active Galactic Nuclei (QSOs, Seyfert galaxies, emission line
radiogalaxies). In addition, we present the spectra of other 19 AGNs included
in a preliminary version of the REX catalog but not in the final one. The
majority (80) of the 90 sources presented in this paper is newly discovered.
Finally, we present the general properties in the radio and in the X-ray band
of all the AGNs discovered so far in the REX survey.Comment: 27 pages. To be published in Astronomy and Astrophysics, Supplement
Series. Better quality figures can be asked to the autho
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