Cross-Calibration of the XMM-Newton EPIC pn & MOS On-Axis Effective Areas Using 2XMM Sources

We aim to examine the relative cross-calibration accuracy of the on-axis effective areas of the XMM-Newton EPIC pn and MOS instruments. Spectra from a sample of 46 bright, high-count, non-piled-up isolated on-axis point sources are stacked together, and model residuals are examined to characterize the EPIC MOS-to-pn inter-calibration. The MOS1-to-pn and MOS2-to-pn results are broadly very similar. The cameras show the closest agreement below 1 keV, with MOS excesses over pn of 0-2% (MOS1/pn) and 0-3% (MOS2/pn). Above 3 keV, the MOS/pn ratio is consistent with energy-independent (or only mildly increasing) excesses of 7-8% (MOS1/pn) and 5-8% (MOS2/pn). In addition, between 1-2 keV there is a `silicon bump' - an enhancement at a level of 2-4% (MOS1/pn) and 3-5% (MOS2/pn). Tests suggest that the methods employed here are stable and robust. The results presented here provide the most accurate cross-calibration of the effective areas of the XMM-Newton EPIC pn and MOS instruments to date. They suggest areas of further research where causes of the MOS-to-pn differences might be found, and allow the potential for corrections to and possible rectification of the EPIC cameras to be made in the future.Comment: 8 Pages, 2 figures (3 panels), 1 table. Accepted for publication in A&

Potential solar axion signatures in X-ray observations with the XMM-Newton observatory

The soft X-ray flux produced by solar axions in the Earth's magnetic field is evaluated in the context of ESA's XMM-Newton observatory. Recent calculations of the scattering of axion-conversion X-rays suggest that the sunward magnetosphere could be an observable source of 0.2-10 keV photons. For XMM-Newton, any conversion X-ray intensity will be seasonally modulated by virtue of the changing visibility of the sunward magnetic field region. A simple model of the geomagnetic field is combined with the ephemeris of XMM-Newton to predict the seasonal variation of the conversion X-ray intensity. This model is compared with stacked XMM-Newton blank sky datasets from which point sources have been systematically removed. Remarkably, a seasonally varying X-ray background signal is observed. The EPIC count rates are in the ratio of their X-ray grasps, indicating a non-instrumental, external photon origin, with significances of 11(pn), 4(MOS1) and 5(MOS2) sigma. After examining the constituent observations spatially, temporally and in terms of the cosmic X-ray background, we conclude that this variable signal is consistent with the conversion of solar axions in the Earth's magnetic field. The spectrum is consistent with a solar axion spectrum dominated by bremsstrahlung- and Compton-like processes, i.e. axion-electron coupling dominates over axion-photon coupling and the peak of the axion spectrum is below 1 keV. A value of 2.2e-22 /GeV is derived for the product of the axion-photon and axion-electron coupling constants, for an axion mass in the micro-eV range. Comparisons with limits derived from white dwarf cooling may not be applicable, as these refer to axions in the 0.01 eV range. Preliminary results are given of a search for axion-conversion X-ray lines, in particular the predicted features due to silicon, sulphur and iron in the solar core, and the 14.4 keV transition line from 57Fe.Comment: Accepted for publication in MNRAS. 67 pages total, including 39 figures, 6 table

Complex X-ray spectral variability in Mkn 421 observed with XMM-Newton

The bright blazar Mkn 421 has been observed four times for uninterrupted durations of ~ 9 - 13 hr during the performance verification and calibration phases of the XMM-Newton mission. The source was strongly variable in all epochs, with variability amplitudes that generally increased to higher energy bands. Although the detailed relationship between soft (0.1 - 0.75 keV) and hard (2 - 10 keV) band differed from one epoch to the next, in no case was there any evidence for a measurable interband lag, with robust upper limits of $| \tau | < 0.08$ hr in the best-correlated light curves. This is in conflict with previous claims of both hard and soft lags of ~1 hr in this and other blazars. However, previous observations suffered a repeated 1.6 hr feature induced by the low-Earth orbital period, a feature that is not present in the uninterrupted XMM-Newton data. The new upper limit on $|\tau|$ leads to a lower limit on the magnetic field strength and Doppler factor of B \delta^{1/3} \gs 4.7 G, mildly out of line with the predictions from a variety of homogeneous synchrotron self-Compton emission models in the literature of $B \delta^{1/3} = 0.2 - 0.8$ G. Time-dependent spectral fitting was performed on all epochs, and no detectable spectral hysteresis was seen. We note however that the source exhibited significantly different spectral evolutionary behavior from one epoch to the next, with the strongest correlations in the first and last and an actual divergance between soft and hard X-ray bands in the third. This indicates that the range of spectral variability behavior in Mkn 421 is not fully described in these short snippets; significantly longer uninterrupted light curves are required, and can be obtained with XMM-Newton.Comment: 21 pages, 4 figures, accepted for ApJ, scheduled for August 1, 200

High Temporal Resolution XMM Monitoring of PKS 2155-304

The bright, strongly variable BL Lac object PKS 2155-304 was observed by XMM for two essentially uninterrupted periods of ~11 and 16 hr on 30-31 May 2000. The strongest variations occurred in the highest energy bands. After scaling for this effect, the three softest bands (0.1-1.7 keV) showed strong correlation with no measurable lag to reliable limits of \tau \ls 0.3 hr. However, the hardest band (~3 keV) was less well-correlated with the other three, especially on short time scales, showing deviations of ~10-20% in ~1 hr although, again, no significant interband lag was detected. This result and examination of previous ASCA and BeppoSAX cross-correlation functions suggest that previous claims of soft lags on time scales of 0.3-4 hr could well be an artifact of periodic interruptions due to Earth-occultation every 1.6 hr. Previous determinations of the magnetic field/bulk Lorentz factor were therefore premature, as these data provide only a lower limit of B \gamma^{1/3} \gs 2.5 G. The hardest band encompasses the spectral region above the high-energy break; its enhanced variability could be indicating that the break energy of the synchrotron spectrum, and therefore of the underlying electron energy distribution, changes independently of the lower energies.Comment: 13 pages, 3 figures, accepted by Ap

Timing analysis of the isolated neutron star RX J0720.4-3125

We present a combined analysis of XMM-Newton, Chandra and Rosat observations of the isolated neutron star RXJ0720.4-3125, spanning a total period of \sim 7 years. We develop a maximum likelihood periodogramme for our analysis based on the \Delta C-statistic and the maximum likelihood method, which are appropriate for the treatment of sparse event lists. Our results have been checked "a posteriori" by folding a further BeppoSAX dataset with the period predicted at the time of that observation: the phase is found to be consistent. The study of the spin history and the measure of the spin-down rate is of extreme importance in discriminating between the possible mechanisms suggested for the nature of the X-ray emission. The value of \dot P, here measured for the first time, is \approx 10^{-14} s/s. This value can not be explained in terms of torque from a fossil disk. When interpreted in terms of dipolar losses, it gives a magnetic field of B \approx 10^{13} G, making also implausible that the source is accreting from the underdense surroundings. On the other hand, we also find unlikely that the field decayed from a much larger value (B\approx 10^{15} G, as expected for a magnetar powered by dissipation of a superstrong field) since this scenario predicts a source age of \approx 10^4 yrs, too young to match the observed X-ray luminosity. The observed properties are more compatible with a scenario in which the source is \approx 10^6 yrs old, and its magnetic field has not changed substantially over the lifetime.Comment: 11 Pages, 6 Figures. Accepted for publication in MNRA

Educação a distância: bibliotecas de pólos de apoio presencial e bibliotecários

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências da Educação, Programa de Pós-Graduação em Ciência da Informação, Florianópolis, 2009.O cenário da sociedade passa por mudanças contínuas, com destaque no aspecto de tratamento da informação e na relevância da educação, especialmente nas universidades ou Instituições Federais de Ensino Superior, no Brasil e no mundo. Nesse cenário, a informação é um elemento crucial para a construção dos alicerces da sociedade da informação. Justifica-se o estudo da Educação a Distância neste trabalho pela expansão da educação nas Instituições Federais de Ensino Superior brasileiras por meio do avanço dos canais e suportes eletrônicos por onde a informação trafega, chegando aos pontos mais remotos do país. Essa pesquisa apresenta cinco modelos de sistemas institucionais de Educação a Distância que se concentram diretamente em atender as necessidades do aluno, ou seja, o aluno como centro do processo de aprendizagem, além dos papéis que os bibliotecários desenvolvem nos sistemas de Educação a Distância e bibliotecas de Pólos de Apoio Presencial. Portanto, este estudo teve por objetivo analisar a atuação dos bibliotecários na Educação a Distância dos cursos de graduação e pós-graduação à distância nos Pólos de Apoio Presencial da Universidade Aberta do Brasil. Trata-se de um estudo de natureza exploratória e descritiva com abordagem quantiqualitativa, sendo que o método empregado foi o estudo de campo. Os instrumentos utilizados para coleta de dados foram questionários e entrevistas. Dois grupos de atores que integraram o universo dessa pesquisa responderam os questionários e foram entrevistados: Trinta Coordenadores de Pólos de Apoio Presencial e três Coordenadores de Produção de Materiais de Educação a Distância. No primeiro grupo de atores, o resultado em relação à existência de bibliotecas de Pólos de Apoio Presencial é de 76,7%, e 50% afirmam que essas bibliotecas possuem menos de 500 livros no acervo. A falta de bibliotecários nos Pólos de Apoio Presencial é de 86,7%, e 13,3% das respostas afirmam a existência desse profissional nesse cenário em dedicação em tempo parcial. No segundo grupo de atores, um participante afirma a existência de bibliotecários formados nas Equipes de Produção de Material de Educação a Distância em tempo parcial, e os outros dois afirmam a inexistência desses profissionais nesse cenário. Os padrões e normas de formatação dos materiais mais utilizados pelas equipes de produção de material de Educação a Distância, são o MEC e ABNT. Evidencia-se que os Pólos de Apoio Presencial estão sendo credenciados com a existência de bibliotecas e com a falta do ator principal para a organização da informação nesses ambientes, o bibliotecário. As equipes de produção de material de Educação a Distância contam com poucos bibliotecários na padronização de processos documentais para integração dos sistemas de Educação a Distância.The scenario of the company undergoes continuous change, especially in the aspect of information handling and relevance of education, especially in universities and Federal Institutions of Higher Education in Brazil and the world. In this scenario, the information is crucial to the construction of the cornerstones of the information society. It is appropriate to the study of distance education in this work by the expansion of education in the Federal Institutions of Higher Education in Brazil through the advancement of electronic media and channels through which information travels, reaching the farthest reaches of the country. This survey presents five models of institutional systems of Distance Education that focus directly on meeting the needs of the student, or student-centered learning process, and the roles that librarians have developed systems of Distance Education and libraries Poles Support Classroom. Therefore, this study aimed to analyze the performance of librarians in Distance Education of undergraduate and graduate distance in Poles Support Classroom in the Open University Brazil. This is a study of exploratory and descriptive with quantitative and qualitative approach, and the method used was the field study. The instruments used to collect data were questionnaires and interviews. Two groups of actors who comprised the universe of this research answered the questionnaires and were interviewed: Thirty Coordinators Classroom Support Poles and three Coordinators Production Materials Distance Education. In the first group of actors, the result for the existence of libraries of Poles Support Attendance is 76.7% and 50 say that these libraries have fewer than 500 books in the collection. The lack of librarians in centers of support attendance is only 86.7%, and 13.3% of respondents claim the existence of a trader in this scenario, in part-time dedication. In the second group of actors, one participant said that there are librarians trained in Teams to Produce Material for Distance Education, but in time, and the other two say the lack of professionals in this scenario. The standards and format of the materials most used by teams of production of material for Distance Education are the MEC and ABNT. It is evident that the Poles to Support Classroom being accredited with the existence of libraries and the lack of leading main the organization of information in these environments, the librarian. Teams Production of Material for Distance Education has few librarians in the standardization of document processes for integrated systems for Distance Education

The Diversity of Tropical Orchids of South Papua

Papua is an area with very wide range, from lowland with altitude 0 m to highland area with 4730 m above sea level. Orchids species constitute the greater part of orchids diversity, which can grow on the bare branches of tall trees, or embedded in moss dripping in wet and cool mountain forests, as well as in the eternal shade of tropical rain forest. Numerous plants world-wide are threatened with extinction because of degradation or destruction of their habitat. Orchids are among the most threatened plants of all, especially when pressure from dealers and collectors aggravales the problems. South Papua is a lowland area with the elevation around 0-7 m above sea level, temperature 23-300 C, and 1500 m rainfall per year. The aims of these investigations were to explore the diversity of tropical orchids in South Papua. The exploration and collection were done in Asmat, Boven Digul, Mappi, and Merauke. The study found 22 genera and 75 species, mostly are epiphytic. Key words: orchids, exploration, diversity, South Papua. 

Statistical evaluation of the flux cross-calibration of the XMM-Newton EPIC cameras

The second XMM-Newton serendipitous source catalogue, 2XMM, provides the ideal data base for performing a statistical evaluation of the flux cross-calibration of the XMM-Newton European Photon Imaging Cameras (EPIC). We aim to evaluate the status of the relative flux calibration of the EPIC cameras on board XMM-Newton (MOS1, MOS2, and pn) and investigate the dependence of the calibration on energy, position in the field of view of the X-ray detectors, and lifetime of the mission. We compiled the distribution of flux percentage differences for large samples of 'good quality' objects detected with at least two of the EPIC cameras. The mean offset of the fluxes and dispersion of the distributions was then found by Gaussian fitting. Count rate to flux conversion was performed with a fixed spectral model. The impact on the results of varying this model was investigated. Excellent agreement was found between the two EPIC MOS cameras to better than 4% from 0.2 keV to 12.0 keV. MOS cameras register 7-9% higher flux than pn below 4.5 keV and 10-13% flux excess above 4.5 keV. No evolution of the flux ratios is seen with time, except at energies below 0.5 keV, where we found a strong decrease in the MOS to pn flux ratio with time. This effect is known to be due to a gradually degrading MOS redistribution function. The flux ratios show some dependence on distance from the optical axis in the sense that the MOS to pn flux excess increases with off-axis angle. Furthermore, in the 4.5-12.0 keV band there is a strong dependence of the MOS to pn excess flux on the azimuthal-angle. These results strongly suggest that the calibration of the Reflection Grating Array (RGA) blocking factors is incorrect at high energies. Finally, we recommend ways to improve the calculation of fluxes in future versions of XMM-Newton source catalogues.Comment: 11 pages, 10 figures, 3 tables. Abridged Abstract. Accepted for publication in Astronomy and Astrophysic