235 research outputs found

    X-ray variability with WFXT: AGNs, transients and more

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    The Wide Field X-ray Telescope (WFXT) is a proposed mission with a high survey speed, due to the combination of large field of view (FOV) and effective area, i.e. grasp, and sharp PSF across the whole FOV. These characteristics make it suitable to detect a large number of variable and transient X-ray sources during its operating lifetime. Here we present estimates of the WFXT capabilities in the time domain, allowing to study the variability of thousand of AGNs with significant detail, as well as to constrain the rates and properties of hundreds of distant, faint and/or rare objects such as X-ray Flashes/faint GRBs, Tidal Disruption Events, ULXs, Type-I bursts etc. The planned WFXT extragalactic surveys will thus allow to trace variable and transient X-ray populations over large cosmological volumes.Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in Bologna, Italy, Nov. 25-26 2009 (arXiv:1010.5889). To appear in Memorie della Societ\`a Astronomica Italiana 2010 - Minor corrections to text

    AGN in overdense environments at high-zz with AXIS

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    Overdense regions at high redshift (z2z \gtrsim 2) are perfect laboratories to study the relations between environment and SMBH growth, and the AGN feedback processes on the surrounding galaxies and diffuse gas. In this white paper, we discuss how AXIS will 1) constrain the AGN incidence in protoclusters, as a function of parameters such as redshift, overdensity, mass of the structure; 2) search for low-luminosity and obscured AGN in the satellite galaxies of luminous QSOs at z>6z>6, exploiting the large galaxy density around such biased objects; 3) probe the AGN feedback on the proto-ICM via the measurement of the AGN contribution to the gas ionization and excitation, and the detection of extended X-ray emission from the ionized gas and from radio jets; 4) discover new large-scale structures in the wide and deep AXIS surveys as spikes in the redshift distribution of X-ray sources. These goals can be achieved only with an X-ray mission with the capabilities of AXIS, ensuring a strong synergy with current and future state-of-the-art facilities in other wavelengths. This White Paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS White Papers can be found at http://axis.astro.umd.edu/ with a mission overview at https://arxiv.org/abs/2311.00780.Comment: 8 pages, 3 figures. This White Paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS White Papers can be found at the AXIS website (http://axis.astro.umd.edu/) with a mission overview at arXiv:2311.0078

    Endovascular repair of abdominal infrarenal penetrating aortic ulcers: a prospective observational study.

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    Abstract Objective Penetrating atherosclerotic ulcer generally occurs in elderly patients with systemic atherosclerosis, predominantly in the descending thoracic aorta, and it is uncommon in the infrarenal aorta. We reviewed our experience of endovascular treatment of penetrating aortic ulcer in the infrarenal aorta. Methods In the last 4years, out of 348 patients who underwent abdominal aortic procedures, a total of 13 patients (12 men and 1 woman) were found to have an abdominal penetrating aortic ulcer, corresponding to an incidence of 3.7%. Mean age was 73±7years. All patients had hypertension. Three lesions were discovered incidentally and 10 were symptomatic. All patients underwent endovascular treatment in the operating room. Follow-up included CT-A control at 1, 4 and 12months after the intervention, and yearly thereafter. Results Primary technical success was 100%. No postoperative death was observed. Mean operative time was 100±29min. Mean blood loss was 168±133ml. No patient required intensive care unit stay. We observed one major complication (transient ischemic attack). Mean hospital stay was 4±1days. During a mean follow-up period of 26months no endoleak, aneurysm evolution or stent graft failure was recognized in any patient. One patient died 24months after the intervention after a stroke. Conclusions In our experience, endovascular or repair of infrarenal aortic ulcer appears feasible, and midterm results satisfactory

    Complications after endovascular stent-grafting of thoracic aortic diseases

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    BACKGROUND: To update our experience with thoracic aortic stent-graft treatment over a 5-year period, with special consideration for the occurrence and management of complications. METHODS: From December 2000 to June 2006, 52 patients with thoracic aortic pathologies underwent endovascular repair; there were 43 males (83%) and 9 females, mean age 63 ± 19 years (range 17–87). Fourteen patients (27%) were treated for degenerative thoracic aortic aneurysm, 12 patients (24%) for penetrating aortic ulcer, 8 patients (15%) for blunt traumatic injury, 7 patients (13%) for acute type B dissection, 6 patients (11%) for a type B dissecting aneurysm; 5 patients (10%) with thoraco-abdominal aortic aneurysms were excluded from the analyses. Fifteen patients (32%) underwent emergency treatment. Overall, mean EuroSCORE was 9 ± 3 (median 15, range 3–19). All procedures were performed in the theatre under general anesthesia. All complications occurring during hospitalisation were recorded. Follow-up protocol featured CT-A, and chest X-rays 1, 4 and 12 months after intervention, and annually thereafter. RESULTS: Primary technical success was achieved in all patients; procedures never aborted because of access difficulty. Conversion to standard open repair was never required. Mean duration of the procedure was 119 ± 75 minutes (median 90, range 45–285). Mean blood loss was 254 mL (range 50–1200 mL). The mean length of the aorta covered by the SGs was 192 ± 21 mm (range 100–360). The LSA was over-stented in 17 cases (17/47, 36%). Overall 30-day operative mortality was 6.4% (3/47). Major complications included pneumonia (n = 9), cerebrovascular accidents (n = 4), arrhythmia (n = 4), acute renal failure (n = 3), and colic ischemia (n = 1). Overall, endoleak rate was 14%. CONCLUSION: Although this report is a retrospective and not comparative analysis of thoracic aortic repair, the combined minor and major morbidity rate was lower than previous reported to results of either electively and emergency performed conventional repair

    Pure laparoscopic formal right hepatectomy versus anatomical posterosuperior segmental resections : a comparative study

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    Background: To analyze the differences in perioperative outcomes between laparoscopic formal right hepatectomies (RH) and laparoscopic anatomical posterosuperior (PS) resections, including segmentectomies in PS segment SVII and right posterior sectionectomies (segment VI and VII resection). Methods: A retrospective analysis of all patients undergoing laparoscopic formal RHs and anatomical PS resections, including segmentectomies in PS segment SVII and right posterior sectionectomies (segment VI and VII resection), between January 2010 and August 2017 was performed. The two groups were compared in terms of patients’ characteristics, intraoperative parameters, and short-term outcomes. Results: Sixty-eight patients were included of which 32 RHs and 36 anatomical PS resections. In the PS resection group, 18 had a segmentectomy of segment VII and 18 had a bisegmentectomy of both segments VI and VII. Patients’ preoperative data were comparable. The lesion size was higher in the RHs (P<0.001). A significant shorter operative time was found in the PS group: 280 [230–315] vs. 357 [300–463] min in the RH group (P<0.001). Blood loss was comparable: 520 [390–906] in the RHs vs. 560 [370–1,030] in the PS group (P=0.595). The overall morbidity rate was comparable being 25% in the RHs and 22.2% in the PS group (P=1.000). A longer length of stay (LOS) {7 [5–8] vs. 5 [4–7] days, P=0.012} and higher readmission rate (12.5% vs. 0%, P=0.044) was observed in the RHs compared to the PS cohort. Concerning surgical margins, the R0 rate was comparable in the two groups; 90.9% in the RHs vs. 95.2% in the PS group (P=1.000). Conclusions: When deemed feasible based on lesion position and size, the laparoscopic parenchyma-preserving approach using anatomical PS segmental resections is associated with shorter hospital stay and a lower readmission rate in respect to formal RH. Overall, short-term surgical parameters indicated that both procedures are safe and feasible in experienced hands, however both demand a great deal of technical expertise

    The Chandra Deep Field South: the 1 Million Second

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    We present the main results from our 940 ksec observation of the Chandra Deep Field South (CDFS), using the source catalog described in an accompanying paper (Giacconi et al. 2001). We extend the measurement of source number counts to 5.5e-17 erg/cm^2/s in the soft 0.5-2 keV band and 4.5e-16 erg/cm^2/s in the hard 2-10 keV band. The hard band LogN-LogS shows a significant flattening (slope~=0.6) below ~1e-14 erg/cm^2/s, leaving at most 10-15% of the X-ray background (XRB) to be resolved, the main uncertainty lying in the measurement of the total flux of the XRB. On the other hand, the analysis in the very hard 5-10 keV band reveals a relatively steep LogN-LogS (slope ~=1.3) down to 1e-15 erg/cm^2/s. Together with the evidence of a progressive flattening of the average X-ray spectrum near the flux limit, this indicates that there is still a non negligible population of faint hard sources to be discovered at energies not well probed by Chandra, which possibly contribute to the 30 keV bump in the spectrum of the XRB. We use optical redshifts and identifications, obtained with the VLT, for one quarter of the sample to characterize the combined optical and X-ray properties of the CDFS sample. Different source types are well separated in a parameter space which includes X-ray luminosity, hardness ratio and R-K color. Type II objects, while redder on average than the field population, have colors which are consistent with being hosted by a range of galaxy types. Type II AGN are mostly found at z<~1, in contrast with predictions based on AGN population synthesis models, thus suggesting a revision of their evolutionary parameters.Comment: Accepted by The Astrophysical Journal, 24 pages, 8 figures, 1 color jpg plate (fig.1

    Surgical treatment of malignant involvement of the inferior vena cava

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    BACKGROUND: Resection and replacement of the inferior vena cava to remove malignant disease is a formidable procedure. The purpose of this review is to describe our experience with regard to patient selection, operative technique, and early and late outcome. METHODS: The authors retrospectively reviewed a 12-year series of 11 patients; there were 10 males, with a mean age 57 ± 13 years (range 27–72) who underwent caval thrombectomy and/or resection for primary (n = 9) or recurrent (n = 2) vena cava tumours. Tumour location and type, clinical presentation, the segment of vena cava treated, graft patency, and tumour recurrence and survival data were collected. Late follow-up data were available for all patients. Graft patency was determined before hospital discharge and in follow-up by CT scan or ultrasonography. More than 80% of patients had symptoms from their caval involvement. The most common pathologic diagnosis was renal cell carcinoma (n = 6), and hepatocarcinoma (n = 2). In all but 2 patients, inferior vena cava surgical treatment was associated with multivisceral resection, including extended nephrectomy (n = 5), resection of neoplastic mass (n = 3), major hepatic resection (n = 2), and adrenal gland resection (n = 1). Prosthetic repair was performed in 5 patients (45%). RESULTS: There were no early deaths. Major complications occurred in 1 patient (9%). Mean length of stay was 16 days. Late graft thrombosis or infection did not occur. The mean follow-up was 22.7 months (range 6–60). There have been no other late graft-related complications. All late deaths were caused by the progression of malignant disease and the actuarial survival rate was 100% at 1 year. Mean survival was 31 months (median 15). CONCLUSION: Aggressive surgical management may offer the only chance for cure or palliation for patients with primary or secondary caval tumours. Our experience confirms that vena cava surgery for tumours may be performed safely with low graft-related morbidity and good patency in carefully selected patients

    Unveiling hidden active nuclei in MaNGA star-forming galaxies with HeIIλ\lambda4686 line emission

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    Nebular HeIIλ\lambda4686\AA~line emission is useful to unveil active galactic nuclei (AGN) residing in actively star-forming (SF) galaxies, typically missed by the standard BPT classification. Here we adopt the HeII diagnostic to identify hidden AGN in the Local Universe using for the first time spatially-resolved data from the Data Release 15 of the Mapping Nearby Galaxies at APO survey (MaNGA DR15). By combining results from HeII and BPT diagnostics, we overall select 459 AGN host candidates (\sim10% in MaNGA DR15), out of which 27 are identified as AGN by the HeII diagram only. The HeII-only AGN population is hosted by massive (M1010_*\gtrsim10^{10} M_{\odot}) SF Main Sequence galaxies, and on average less luminous than the BPT-selected AGN. Given the HeII line faintness, we revisit our census accounting for incompleteness effects due to the HeII sensitivity limit of MaNGA. We thus obtain an overall increased fraction (11%) of AGN in MaNGA compared to the BPT-only census (9%), which further increases to 14% for galaxies more massive than 101010^{10} M_{\odot}; interestingly, on the SF Main Sequence the increase is by about a factor of 2. A substantial number of AGN in SF galaxies points to significant, coeval star formation and black hole accretion, consistently with results from hydrodynamical simulations and with important implications on quenching scenarios. In view of exploring unprecedented high redshifts with JWST and new ground-based facilities, revisiting the standard BPT classification through novel emission-line diagnostics is fundamental to discover AGN in highly SF environments.Comment: 13 pages, 12 figures. Accepted for publication in MNRA

    Piercing Through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields: I. X-ray Spectral and Long-term Variability Analyses

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    We present a detailed X-ray spectral analysis of 1152 AGNs selected in the Chandra Deep Fields (CDFs), in order to identify highly obscured AGNs (NH>1023 cm2N_{\rm H} > 10^{23}\ \rm cm^{-2}). By fitting spectra with physical models, 436 (38%) sources with LX>1042 erg s1L_{\rm X} > 10^{42}\ \rm erg\ s^{-1} are confirmed to be highly obscured, including 102 Compton-thick (CT) candidates. We propose a new hardness-ratio measure of the obscuration level which can be used to select highly obscured AGN candidates. The completeness and accuracy of applying this method to our AGNs are 88% and 80%, respectively. The observed logN-logS relation favors cosmic X-ray background models that predict moderate (i.e., between optimistic and pessimistic) CT number counts. 19% (6/31) of our highly obscured AGNs that have optical classifications are labeled as broad-line AGNs, suggesting that, at least for part of the AGN population, the heavy X-ray obscuration is largely a line-of-sight effect, i.e., some high-column-density clouds on various scales (but not necessarily a dust-enshrouded torus) along our sightline may obscure the compact X-ray emitter. After correcting for several observational biases, we obtain the intrinsic NH distribution and its evolution. The CT-to-highly-obscured fraction is roughly 52% and is consistent with no evident redshift evolution. We also perform long-term (~17 years in the observed frame) variability analyses for 31 sources with the largest number of counts available. Among them, 17 sources show flux variabilities: 31% (5/17) are caused by the change of NH, 53% (9/17) are caused by the intrinsic luminosity variability, 6% (1/17) are driven by both effects, and 2 are not classified due to large spectral fitting errors.Comment: 32 pages, 21 figures, 9 tables, accepted for publication in Ap
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