947 research outputs found
An X-ray Survey in SA 57 with XMM-Newton
The maximum number density of Active Galactic Nuclei (AGNs), as deduced from
X-ray studies, occurs at z<~1, with lower luminosity objects peaking at smaller
redshifts. Optical studies lead to a different evolutionary behaviour, with a
number density peaking at z~2 independently of the intrinsic luminosity, but
this result is limited to active nuclei brighter than the host galaxy. A
selection based on optical variability can detect low luminosity AGNs (LLAGNs),
where the host galaxy light prevents the identification by non-stellar colours.
We want to collect X-ray data in a field where it exists an optically-selected
sample of "variable galaxies'', i.e. variable objects with diffuse appearance,
to investigate the X-ray and optical properties of the population of AGNs,
particularly of low luminosity ones, where the host galaxy is visible. We
observed a field of 0.2 deg^2 in the Selected Area 57, for 67ks with
XMM-Newton. We detected X-ray sources, and we correlated the list with a
photographic survey of SA 57, complete to B_J~23 and with available
spectroscopic data. We obtained a catalogue of 140 X-ray sources to limiting
fluxes 5x10^-16, 2x10^-15 erg/cm^2/s in the 0.5-2 keV and 2-10 keV
respectively, 98 of which are identified in the optical bands. The X-ray
detection of part of the variability-selected candidates confirms their AGN
nature. Diffuse variable objects populate the low luminosity side of the
sample. Only 25/44 optically-selected QSOs are detected in X-rays. 15% of all
QSOs in the field have X/O<0.1.Comment: 13 pages, 6 figures, 4 tables, A&A in pres
On the computation of Wasserstein barycenters
The Wasserstein barycenter is an important notion in the analysis of high dimensional data with a broad range of applications in applied probability, economics, statistics, and in particular to clustering and image processing. In this paper, we state a general version of the equivalence of the Wasserstein barycenter problem to the n-coupling problem. As a consequence, the coupling to the sum principle (characterizing solutions to the n-coupling problem) provides a novel criterion for the explicit characterization of barycenters. Based on this criterion, we provide as a main contribution the simple to implement iterative swapping algorithm (ISA) for computing barycenters. The ISA is a completely non-parametric algorithm which provides a sharp image of the support of the barycenter and has a quadratic time complexity which is comparable to other well established algorithms designed to compute barycenters. The algorithm can also be applied to more complex optimization problems like the k-barycenter problem
Blazar surveys with WMAP and Swift
We present the preliminary results from two new surveys of blazars that have
direct implications on the GLAST detection of extragalactic sources from two
different perspectives: microwave selection and a combined deep X-ray/radio
selection. The first one is a 41 GHz flux-limited sample extracted from the
WMAP 3-yr catalog of microwave point sources. This is a statistically well
defined sample of about 200 blazars and radio galaxies, most of which are
expected to be detected by GLAST. The second one is a new deep survey of
Blazars selected among the radio sources that are spatially coincident with
serendipitous sources detected in deep X-ray images (0.3-10 keV) centered on
the Gamma Ray Bursts (GRB) discovered by the Swift satellite. This sample is
particularly interesting from a statistical viewpoint since a) it is unbiased
as GRBs explode at random positions in the sky, b) it is very deep in the X-ray
band (\fx \simgt \ergs) with a position accuracy of a few
arc-seconds, c) it will cover a fairly large (20-30 square deg.) area of sky,
d) it includes all blazars with radio flux (1.4 GHz) larger than 10 mJy, making
it approximately two orders of magnitude deeper than the WMAP sample and about
one order of magnitude deeper than the deepest existing complete samples of
radio selected blazars, and e) it can be used to estimate the amount of
unresolved GLAST high latitude gamma-ray background and its anisotropy
spectrum.Comment: 3 pages, 3 figures, to appear in Proc. of the 1st GLAST Symposium,
Feb 5-8, 2007, Stanford, AIP, Eds. S. Ritz, P. F. Michelson, and C. Meega
Evidence for T Tauri-like emission in the EXor V1118 Ori from near-IR and X-ray data
We present a near-IR study of the EXor variable V1118 Ori, performed by
following a slightly declining phase after a recent outburst. In particular,
the near-IR (0.8 - 2.3 micron) spectrum, obtained for the first time, shows a
large variety of emission features of the HI and HeI recombination and CO
overtone. By comparing the observed spectrum with a wind model, a mass loss
rate value is derived along with other parameters whose values are typical of
an accreting T Tauri star. In addition, we have used X-ray data from the XMM
archive, taken in two different epochs during the declining phase monitored in
IR. X-ray emission (in the range 0.5 - 10 keV) permits to derive several
parameters which confirm the T Tauri nature of the source. In the near-IR the
object maintains a low visual extinction during all the activity phases,
confirming that variable extinction does not contribute to brightness
variations. The lack of both a significant amount of circumstellar material and
any evidence of IR cooling from collimated jet/outflow driven by the source,
indicates that, at least this member of the EXor class, is in a late stage of
the Pre-Main Sequence evolution. In the X-ray regime, an evident fading is
present, detected in the post-outburst phase, that cannot be reconciled with
the presence of any absorbing material. This circumstance, combined with the
persistence (in the pre- and post-outburst phases) of a temperature component
at about 10 MK, suggests that accretion has some influence in regulating the
coronal activity
The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow
We present the best sensitivity and angular resolution maps of the molecular
disk and outflow of Mrk 231, as traced by CO observations obtained with
IRAM/PdBI, and we analyze archival Chandra and NuSTAR observations. We
constrain the physical properties of both the molecular disk and outflow, the
presence of a highly-ionized ultra-fast nuclear wind, and their connection. The
molecular outflow has a size of ~1 kpc, and extends in all directions around
the nucleus, being more prominent along the south-west to north-east direction,
suggesting a wide-angle biconical geometry. The maximum projected velocity of
the outflow is nearly constant out to ~1 kpc, thus implying that the density of
the outflowing material decreases from the nucleus outwards as . This
suggests that either a large part of the gas leaves the flow during its
expansion or that the bulk of the outflow has not yet reached out to ~1 kpc,
thus implying a limit on its age of ~1 Myr. We find and erg s.
Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow
(UFO) with velocity -20000 km s, , and momentum load .We find as predicted for outflows undergoing an energy
conserving expansion. This suggests that most of the UFO kinetic energy is
transferred to mechanical energy of the kpc-scale outflow, strongly supporting
that the energy released during accretion of matter onto super-massive black
holes is the ultimate driver of giant massive outflows. We estimate a momentum
boost . The ratios and agree
with the requirements of the most popular models of AGN feedback.Comment: 16 pages, 17 figures. Accepted for publication in A&
The Nustar Extragalactic Surveys: Overview and Catalog from the Cosmos Field
To provide the census of the sources contributing to the X-ray background peak above 10 keV, NuSTAR is performing extragalactic surveys using a three-tier wedding cake approach. We present the NuSTAR survey of the COSMOS field, the medium sensitivity and medium area tier, covering 1.7 deg2 and overlapping with both Chandra and XMM-Newton data. This survey consists of 121 observations for a total exposure of ~3 Ms. To fully exploit these data, we developed a new detection strategy, carefully tested through extensive simulations. The survey sensitivity at 20% completeness is 5.9, 2.9 and 6.4 x 10^-14 erg/cm2/s in the 3-24 keV, 3-8 keV and 8-24 keV bands, respectively. By combining detections in 3 bands, we have a sample of 91 NuSTAR sources with 10^42 -10^45.5 erg/s luminosities and redshift z=0.04-2.5. Thirty two sources are detected in the 8-24 keV band with fluxes ~100 times fainter than sources detected by Swift-BAT. Of the 91 detections, all but four are associated with a Chandra and/or XMM-Newton point-like counterpart. One source is associated with an extended lower energy X-ray source. We present the X-ray (hardness ratio and luminosity) and optical-to-X-ray properties. The observed fraction of candidate Compton-thick AGN measured from the hardness ratio is between 13-20%. We discuss the spectral properties of NuSTAR J100259+0220.6 (ID 330) at z=0.044, with the highest hardness ratio in the entire sample. The measured column density exceeds 10^24 /cm2, implying the source is Compton-thick. This source was not previously recognized as such without the \u3e10 keV data
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