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

Unprecedented layered coordination polymers of dithiolene group 10 metals: Magnetic and electrical properties

One-pot reactions between Ni(ii), Pd(ii) or Pt(ii) salts and 3,6-dichloro-1,2-benzenedithiol (HSC6H2Cl2SH) in KOH medium under argon lead to a series of bis-dithiolene coordination polymers. X-ray analysis shows the presence of a common square planar complex [M(SC6H2Cl2S)2]2- linked to potassium cations forming either a two-dimensional coordination polymer network for {[K2(μ-H2O)2(μ-thf)(thf)2][M(SC6H2Cl2S)2]}n [M = Ni (1) and Pd (2)] or a one-dimensional coordination polymer for {[K2(μ-H2O)2(thf)6][Pt(SC6H2Cl2S)2]}n (3). In 3 the coordination environment of the potassium ions may slightly change leading to the two-dimensional coordination polymer {[K2(μ-H2O)(μ-thf)2][Pt(SC6H2Cl2S)2]}n (4) that crystallizes together with 3. The physical characterization of compounds 1-3 show similar trends, they are diamagnetic and behave as semiconductorsWe thank financial support from MICINN (MAT2013-46753-C2-1-P, CTQ2014-52758-P and MAT2014-56143-R) and Generalitat Valenciana (PrometeoII/2014/076

Habitat and development. Exploring paths of educational innovation in architecture and urbanism

Han pasado dos décadas desde que aparecieron las primeras asignaturas que incorporaban la habitabilidad básica o la cooperación al desarrollo en la formación del arquitecto en España. Desde entonces, las escuelas de arquitectura han ido incorporando contenidos que son cada vez más demandados, tanto por la sociedad como por los propios alumnos. La crisis económica iniciada en 2008, o los Objetivos de Desarrollo Sostenible aprobados en 2015 por Naciones Unidas, nos deben hacer reflexionar sobre la centralidad de estos temas en la formación de la arquitectura y el urbanismo. Desde el año de su creación, en 2001, la asignatura optativa Hábitat y desarrollo se ha propuesto visibilizar la arquitectura social como una parte importante en la formación del arquitecto, en la que se prioriza el proceso arquitectónico, íntimamente relacionado con el habitar (el habitante, los hábitos y su relación con el lugar), frente al producto (el objeto, el edificio, como una síntesis formal de esa arquitectura). En la asignatura se hace una lectura del papel que la cooperación al desarrollo puede jugar en la formación del arquitecto. La participación ciudadana es otro de los temas transversales que se incorporan en la asignatura, formando a los estudiantes en técnicas específicamente aplicables al campo de la arquitectura y del urbanismo. Hábitat y desarrollo se imparte en el primer semestre de quinto curso del grado en arquitectura de la Universidad de Las Palmas de Gran Canaria.Habitat and development. Exploring paths of educational innovation in architecture and urbanism. It has been two decades since the first subjects that incorporated basic habitability or development cooperation appeared in the training of the architect in Spain. Since then the schools of architecture have been incorporating content that is increasingly demanded by both society and students themselves. The economic crisis initiated in 2008 or the Sustainable Development Objectives approved in 2015 by the United Nations should make us reflect on the centrality of these issues in the formation of architecture and urbanism. Since the year of its creation, in 2001, the optional Habitat and Development has been proposed to make visible the social architecture as an important part in the architect’s training, in which the architectural process is prioritized, closely related to the habitat (the inhabitant, the habits and their relation to the place), in front of the product (the object, the building, as a formal synthesis of that architecture). The subject makes a reading of the role that development cooperation can play in the training of the architect. Citizen participation is another of the cross-cutting themes that are incorporated into the subject by training students in techniques specifically applicable to the field of architecture and urbanism. Habitat and development is taught in the first semester of fifth year of the degree in architecture of the University of Las Palmas de Gran Canaria