X-ray spectral variability of seven LINER nuclei with XMM-Newton and Chandra data

One of the most important features in active galactic nuclei (AGN) is the variability of their emission. Variability has been discovered at X-ray, UV, and radio frequencies on time scales from hours to years. Among the AGN family and according to theoretical studies, Low-Ionization Nuclear Emission Line Region (LINER) nuclei would be variable objects on long time scales. Our purpose is to investigate spectral X-ray variability in LINERs and to understand the nature of these kinds of objects, as well as their accretion mechanism. Chandra and XMM-Newton public archives were used to compile X-ray spectra of seven LINER nuclei at different epochs with time scales of years. To search for variability we fit all the spectra from the same object with a set of models, in order to identify the parameters responsible for the variability pattern. We also analyzed the light curves in order to search for short time scale (from hours to days) variability. Whenever possible, UV variability was also studied. We found spectral variability in four objects, with variations mostly related to hard energies (2-10 keV). These variations are due to changes in the soft excess, and/or changes in the absorber, and/or intrinsic variations of the source. Another two galaxies seem not to vary. Short time scale variations during individual observations were not found. Our analysis confirms the previously reported anticorrelation between the X-ray spectral index and the Eddington ratio, and also the correlation between the X-ray to UV flux ratio and the Eddington ratio. These results support an Advection Dominated Accretion Flow (ADAF) as the accretion mechanism in LINERs.Comment: 35 pages, 53 figures, recently accepted pape

X-ray spectral variability of Seyfert 2 galaxies

Variability across the electromagnetic spectrum is a property of AGN that can help constraining the physical properties of these galaxies. This is the third of a serie of papers with the aim of studying the X-ray variability of different families of AGN. The main purpose of this work is to investigate the variability pattern in a sample of optically selected type 2 Seyfert galaxies. We use the 26 Seyferts in the Veron-Cetty and Veron catalogue with data available from Chandra and/or XMM-Newton public archives at different epochs, with timescales ranging from a few hours to years. All the spectra of the same source are simultaneously fitted and we let different parameters to vary in the model. Whenever possible, short-term variations and/or long-term UV flux variations are studied. We divide the sample in Compton-thick, Compton-thin, and changing-look candidates. Short-term variability at X-rays is not found. From the 25 analyzed sources, 11 show long-term variations; eight (out of 11) are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look candidates are also variable. The main driver for the X-ray changes is related to the nuclear power (nine cases), while variations at soft energies or related with absorbers at hard X-rays are less common, and in many cases these variations are accompained with variations of the nuclear continuum. At UV frequencies nuclear variations are nor found. We report for the first time two changing-look candidates, MARK273 and NGC7319. A constant reflection component located far away from the nucleus plus a variable nuclear continuum are able to explain most of our results; the Compton-thick candidates are dominated by reflection, which supresses their continuum making them seem fainter, and not showing variations, while the Compton-thin and changing-look candidates show variations.Comment: Accepted for publication in A&

X-ray spectral variability of LINERs selected from the Palomar sample

Variability is a general property of active galactic nuclei (AGN). At X-rays, the way in which these changes occur is not yet clear. In the particular case of low ionisation nuclear emission line region (LINER) nuclei, variations on months/years timescales have been found for some objects, but the main driver of these changes is still an open question. The main purpose of this work is to investigate the X-ray variability in LINERs, including the main driver of such variations, and to search for eventual differences between type 1 and 2 objects. We use the 18 LINERs in the Palomar sample with data retrieved from Chandra and/or XMM-Newton archives corresponding to observations gathered at different epochs. All the spectra for the same object are simultaneously fitted in order to study long term variations. The nature of the variability patterns are studied allowing different parameters to vary during the spectral fit. Whenever possible, short term variations from the analysis of the light curves and UV variability are studied.Comment: 49 pages, accepted. arXiv admin note: text overlap with arXiv:1305.222

Nodal involvement evaluation in advanced cervical cancer: a single institutional experience

Purpose: To assess the usefulness of different imaging techniques in the detection of nodal involvement in patients with advanced cervical carcinoma. Moreover, to analyze the correlation between the presurgical (FIGO) and postsurgical (pTNM) staging classifications. Materials and Methods: All patients diagnosed with advanced cervical cancer (FIGO Stages IIB-IV) from 2005 to 2012 were selected. The medical charts of 51 patients that underwent presurgical assessment with posterior surgical staging by means of paraaortic lymphadenectomy, were reviewed. Nodal status assessment by computed tomography scan (CT scan), magnetic resonance imaging (MRI), positron emission tomography (PET), and sonography was compared, as well as the size given in imaging techniques compared to the final pathologic report information. Results: Presurgical analysis by CT scan, MRI, PET, and sonography showed pelvic nodal involvement in 51.3% of patients, and para-aortic involvement in 30.8% of cases. CT scan showed positive pelvic nodes in 35% of cases, but pathologic confirmation was observed in just 17.6% of cases. However, MRI resulted in higher rates of up to 48.8% of cases. Concerning para-aortic nodal involvement, CT scan showed positive nodes in 25% of cases, MRI in 3.2% of cases, and the pathologic report in 15.6% of cases. The authors found significant differences between staging groups among both classifications (FIGO vs. pTNM; p < 0.001). Eight cases (15.7%) were understaged by FIGO classification. Conclusions: Despite all imaging techniques available, none has demonstrated to be efficient enough to avoid the systematic study of para-aortic nodal status by means of surgical evaluatio

The Black Hole Binary Nova Scorpii 1994 (GRO J1655-40): An improved chemical analysis

The chemical analysis of secondary stars of low mass X-ray binaries provides an opportunity to study the formation processes of compact objects, either black holes or neutron stars. Following the discovery of overabundances of $\alpha$-elements in the HIRES/Keck spectrum of the secondary star of Nova Scorpii 1994 (Israelian et al. 1999), we obtained UVES/VLT high-resolution spectroscopy with the aim of performing a detailed abundance analysis of this secondary star. Using a $\chi2$-minimization procedure and a grid of synthetic spectra, we derive the stellar parameters and atmospheric abundances of O, Mg, Al, Ca, Ti, Fe and Ni, using a new UVES spectrum and the HIRES spectrum.The abundances of Al, Ca, Ti, Fe and Ni seem to be consistent with solar values, whereas Na, and especially O, Mg, Si and S are significantly enhanced in comparison with Galactic trends of these elements. A comparison with spherically and non-spherically symmetric supernova explosion models may provide stringent constraints to the model parameters as mass-cut and the explosion energy, in particular from the relative abundances of Si, S, Ca, Ti, Fe and Ni. Most probably the black hole in this system formed in a hypernova explosion of a 30--35 \Msun progenitor star with a mass-cut in the range 2--3.5 \Msun. However, these models produce abundances of Al and Na almost ten times higher than the observed values.Comment: New Accepted version for publication in Astronomy and Astrophysics Table 2: Correcte

A note on the behavior of majority voting in multi-class domains with biased annotators

Majority voting is a popular and robust strategy to aggregate different opinions in learning from crowds, where each worker labels examples ac- cording to their own criteria. Although it has been extensively studied in the binary case, its behavior with multiple classes is not completely clear, specifically when annotations are biased. This paper attempts to fill that gap. The behavior of the majority voting strategy is studied in-depth in multi-class domains, emphasizing the effect of annotation bias. By means of a complete experimental setting, we show the limitations of the stan- dard majority voting strategy. The use of three simple techniques that infer global information from the annotations and annotators allows us to put the performance of the majority voting strategy in context.TIN2016-78365-