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 $10^{-15}$ \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

An interview with Roger Cooke

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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 $r^{-2}$. 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 $\dot M_{OF}=[ 500-1000]~ M_{\odot}~yr^{-1}$ and $\dot E_{kin,OF}=[7-10]\times 10^{43}$ erg s$^{-1}$. Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow (UFO) with velocity -20000 km s$^{-1}$, $\dot M_{UFO}=[0.3- 2.1] ~M_\odot yr^{-1}$, and momentum load $\dot P_{UFO}/\dot P_{rad}=[0.2-1.6]$.We find $\dot E_{kin,UFO}\sim \dot E_{kin,OF}$ 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 $\dot P_{OF}/\dot P_{UFO}\approx [30-60]$. The ratios $\dot E_{kin, UFO}/L_{bol,AGN} =[ 1-5]\%$ and $\dot E_{kin,OF}/L_{bol,AGN} = [1-3]\%$ 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