1,721,001 research outputs found
Gamma-ray emission from massive star forming regions
Full text linkRecent radio observations support a picture for star formation where there is accretion of matter onto a central protostar with the ejection of molecular outflows that can affect the surrounding medium. The impact of a supersonic outflow on the ambient gas can produce a strong shock that could accelerate particles up to relativistic energies. A strong evidence of this has been the detection of non-thermal radio emission coming from the jet termination region of some young massive stars. In the present contribution, we study the possible high-energy emission due to the interaction of relativistic particles, electrons and protons, with the magnetic, photon and matter fields inside a giant molecular cloud. Electrons lose energy via relativistic Bremsstrahlung, synchrotron radiation and inverse Compton interactions, and protons cool mainly through inelastic collisions with atoms in the cloud. We conclude that some massive young stellar objects might be detectable at gamma-rays by next generation instruments, both satellite-borne and ground based.Fil: Araudo, Anabella Teresa. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Bosch Ramon, Valentí. Max Planck Institut für Kernphysik; AlemaniaFil: Paredes, Josep Maria. Universidad de Barcelona; Españ
Spectral and Variability Properties of LS 5039 from Radio to very High-Energy Gamma-Rays
No full textMicroquasars are X-ray binaries with relativistic jets. The microquasar LS 5039 turned out to be the first high-energy gamma-ray microquasar candidate due to its likely association with the EGRET source 3EG J1824−1514 [9]. Further theoretical studies supported this association [2], which could be extended to other EGRET sources ([7, 11, 3]). Very recently, [1] have communicated the detection of LS 5039 at TeV energies. This fact confirms the EGRET source association and leaves no doubt about the gamma-ray emitting nature of this object. The aim of the present work is to show that, applying a cold-matter dominated jet model to LS 5039, we can reproduce many of the spectral and variability features observed in this source. Jet physics is explored, and some physical quantities are estimated as a by-product of the performed modeling. Although at the moment only LS 5039 has been detected on the entire electromagnetic spectrum, it does not seem unlikely that other microquasars will show similar spectral properties. Therefore, an in-depth study of the first gamma-ray microquasar, on theoretical grounds supported by observations, can render a useful knowledge applicable elsewhere.Fil: Bosch Ramon, Valentí. Universidad de Barcelona; EspañaFil: Paredes, Josep Maria. Universidad de Barcelona; EspañaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaProceedings of the MPE/USM/MPA/ESO Joint Astronomy Conference HeldMunichAlemaniaEuropean Southern Observator
On the nature of the variable gamma-ray sources at low galactic latitudes
Full text linkPopulation studies of EGRET gamma-ray sources indicate that there is a distinctive population of bright sources at low galactic latitudes. The sources have a distribution consistent with that of young galactic objects, with a concentration toward the inner spiral arms. There is a subgroup that displays strong variability with timescales from days to months. Following an earlier suggestion by Kaufman Bernadó et al. (2002), we explore the possibility that these sources could be high-mass microquasars. Detailed models for the gamma-ray emission that include inverse Compton interactions of electrons in the relativistic jets and photons from all local fields (stellar UV photons, synchrotron photons, soft X-ray photons from the accretion disk, and hard X-ray photons from a corona) are presented. We conclude that microquasars are excellent candidates for the parent population of the subgroup of variable low-latitude EGRET sources.Fil: Bosch Ramon, Valentí. Universidad de Barcelona; EspañaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Paredes, Josep Maria. Universidad de Barcelona; Españ
Gamma-Ray Emission from Microquasars: Leptonic vs. Hadronic Models
No full textSummary. In this work we discuss two different types of models for the high-energy gamma ray production in microquasars. On the one hand, we introduce a new leptonic model where the emission arises from inverse Compton interactions with both internal (synchrotron) and external photon fields, and relativistic Bremsstrahlung from interactions with cold protons in the jet and the stellar wind material. On the other hand, we introduce a hadronic model where the gamma rays are the result of interactions between relativistic protons in the jet and cold protons from the anisotropic stellar wind. Spectral differences and similarities between both types of models are briefly discussed.Fil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Bosch Ramon, Valentí. Universidad de Barcelona; EspañaFil: Paredes, Josep Maria. Universidad de Barcelona; EspañaFil: Orellana, Mariana Dominga. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaProceedings of the MPE/USM/MPA/ESO Joint Astronomy Conference HeldMunichAlemaniaEuropean Southern Observator
Identifying variable gamma-ray sources through radio observations
Full text linkWe present preliminary results of a campaign undertaken with different radio interferometers to observe a sample of the most variable unidentified EGRET sources. We expect to detect which of the possible counterparts of the γ -ray sources (any of the radio emitters in the field) varies in time with similar timescales as the γ -ray variation. If the γ -rays are produced in a jet-like source, as we have modelled theoretically, synchrotron emission is also expected at radio wavelengths. Such radio emission should appear variable in time and correlated with the γ -ray variability.Fil: Paredes, Josep Maria. Universidad de Barcelona; EspañaFil: Martí, Josep. Universidad de Jaén; EspañaFil: Torres, Diego F.. Lawrence Livermore National Laboratory; Estados UnidosFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Combi, Jorge Ariel. Universidad de Jaén; España. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bosch Ramon, Valentí. Universidad de Barcelona; EspañaFil: García Sánchez, J.. Universidad de Barcelona; Españ
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
