This thesis considers the various morphologies of radio supernova remnants (SNRs), and attempts to determine whether their appearance results from the properties of the progenitor star and its supernova explosion, or from the structure of the interstellar medium (ISM) and ambient magnetic field into which a SNR consequently expands. High-resolution observations of Supernova 1987A show a young remnant whose appearance and evolution are completely dominated by the structure of its progenitor wind. A statistical study of the Galactic population of bilateral SNRs demonstrates that the symmetry axes of these remnants run parallel to the Galactic Plane. This result can be explained by the interaction of main sequence stellar wind-bubbles with the ambient magnetic field; expansion of SNRs into the resulting elongated cavities results in a bilateral appearance with the observed alignment. Radio observations of SNR G296.8-00.3 show a double-ringed morphology which is best explained by expansion either into an anisotropic main-sequence progenitor wind or into multiple cavities in the ISM. Data on SNRs G309.2-00.6 and G320.4-01.2 (MSH 15-52) make a strong case that the appearance of both remnants is significantly affected by collimated outflows from a central source; for G309.2-00.6 the source itself is not detected, but for G320.4-01.2 there is now compelling evidence that the remnant is associated with and is interacting with the young pulsar PSR B1509-58. I conclude that, while the youngest SNRs are shaped by their progenitor's circumstellar material, the appearance of most SNRs reflects the properties of the local ISM and magnetic field. Remnants which interact with an associated pulsar or binary system appear to be rare, and are easily distinguished by their unusual and distorted morphologies.

One of the most significant current discussions in Astrophysics relates to the origin of high-energy cosmic rays. According to our current knowledge, the abundance distribution of the elements in cosmic rays at their point of origin indicates, within plausible error limits, that they were initially formed by nuclear processes in the interiors of stars. It is also believed that their energy distribution up to 1018 eV has Galactic origins. But even though the knowledge about potential sources of cosmic rays is quite poor above „ 1015 eV, that is the “knee” of the cosmic-ray spectrum, up to the knee there seems to be a wide consensus that supernova remnants are the most likely candidates. Evidence of this comes from observations of non-thermal X-ray radiation, requiring synchrotron electrons with energies up to 1014 eV, exactly in the remnant of supernovae. To date, however, there is not conclusive evidence that they produce nuclei, the dominant component of cosmic rays, in addition to electrons. In light of this dearth of evidence, γ-ray observations from supernova remnants can offer the most promising direct way to confirm whether or not these astrophysical objects are indeed the main source of cosmic-ray nuclei below the knee. Recent observations with space- and ground-based observatories have established shell-type supernova remnants as GeV-to- TeV γ-ray sources. The interpretation of these observations is however complicated by the different radiation processes, leptonic and hadronic, that can produce similar fluxes in this energy band rendering ambiguous the nature of the emission itself. The aim of this work is to develop a deeper understanding of these radiation processes from a particular shell-type supernova remnant, namely RX J1713.7–3946, using observations of the LAT instrument onboard the Fermi Gamma-Ray Space Telescope. Furthermore, to obtain accurate spectra and morphology maps of the emission associated with this supernova remnant, an improved model of the diffuse Galactic γ-ray emission background is developed. The analyses of RX J1713.7–3946 carried out with this improved background show that the hard Fermi-LAT spectrum cannot be ascribed to the hadronic emission, leading thus to the conclusion that the leptonic scenario is instead the most natural picture for the high-energy γ-ray emission of RX J1713.7–3946. The leptonic scenario however does not rule out the possibility that cosmic-ray nuclei are accelerated in this supernova remnant, but it suggests that the ambient density may not be high enough to produce a significant hadronic γ-ray emission. Further investigations involving other supernova remnants using the improved back- ground developed in this work could allow compelling population studies, and hence prove or disprove the origin of Galactic cosmic-ray nuclei in these astrophysical objects. A break- through regarding the identification of the radiation mechanisms could be lastly achieved with a new generation of instruments such as CTA. / Eine der gegenwärtigen bedeutendsten geführten Diskussionen in der Astrophysik bezieht sich auf den Ursprung der hochenergetischen Kosmischen Strahlung. Nach unserem heutigen Verständnis weist die am Ort des Ursprungs elementare Zusam- mensetzung der Kosmischen Strahlung darauf hin, dass diese zu Beginn mittels nuklearer Prozesse im Inneren von Sternen gebildet wurde. Weiterhin wird ange- nommen, dass die Kosmische Strahlung bis 1018 eV galaktischen Ursprungs ist. Auch wenn das Verständnis über die potentiellen Quellen der Kosmischen Strahlung ober- halb von 1015 eV, dem sogenannten „Knie“ des Spektrums der Kosmischen Strah- lung, lückenhaft ist, so liegt doch der Konsens vor, dass Supernovaüberreste (SNR) die wahrscheinlichsten Quellen für Energien bis 1015 eV sind. Unterstützt wird die- ser Sachverhalt durch Beobachtungen von nichtthermischer Röntgenstrahlung von SNR, deren Emission Elektronen mit Energien bis zu 1014 eV erfordern. Jedoch gibt es bis heute keinen überzeugenden Beweis, dass SNR zusätzlich zu den Elektronen auch Atomkerne, die den dominierenden Anteil in der Kosmischen Strahlung bilden, beschleunigen. Trotz fehlender überzeugender Beweise ermöglichen nun Beobachtungen von SNR im γ-Strahlungsbereich einen vielversprechenden Weg zur Aufklärung der Fra- ge, ob diese astrophysikalischen Objekte in der Tat die Hauptquelle der Kosmischen Strahlung unterhalb des Knies sind. Kürzlich durchgeführte Beobachtungen im Welt- raum und auf der Erdoberfläche haben zu der Erkenntnis geführt, dass schalenartige SNR γ-Strahlung im GeV- und TeV-Bereich emittieren. Die Interpretation dieser Beobachtungen ist jedoch schwierig, da sowohl Atomkerne als auch Elektronen im betrachteten Energiebereich zu ähnlichen γ-Emissionen führen. Dadurch wird die eindeutige Identifizierung der Emission als das Resultat hadronischer oder leptoni- scher Emissionsprozesse erschwert. Das Ziel dieser Arbeit ist es, am Beispiel des schalenartigen SNR RX J1713.7- 3946 ein tieferes Verständnis über die Strahlungsprozesse zu erhalten, indem vom γ-Weltraumteleskop Fermi durchgeführte Beobachtungen analysiert werden. Um ge- naue Spektren und die Ausdehnung der Region der Emission zu erhalten, wird ein verbessertes Modell für die diffuse galaktische γ-Hintergrundstrahlung entwickelt. Die mit diesem verbesserten Hintergrund durchgeführte Analyse von RX J1713.7- 3946 zeigt, dass das vom Fermi-Satelliten beobachtete Spektrum nicht dem hadro- nischen Szenario zugeschrieben werden kann, sodass das leptonische Szenario für die γ-Emissionen von diesem SNR verantwortlich ist. Das leptonische Szenario schließt jedoch nicht die Möglichkeit aus, dass auch Atomkerne in diesem SNR beschleu- nigt werden. Aber es deutet darauf hin, dass die umgebende Teilchendichte nicht ausreichend hoch genug ist, um zu einer signifikanten hadronischen γ-Emission zu führen. Weitere Untersuchungen, die andere SNR in Kombination mit dem hier ent- wickelten verbesserten Modell der Hintergrundstrahlung beinhalten, können Popu- lationsstudien erlauben. Dies könnte klären, ob die SNR tatsächlich die Quellen der galaktischen Kosmischen Strahlung sind. Ein Durchbruch bezüglich der Identi- fikation des Strahlungsmechanismus könnte auch durch eine neue Generation von Beobachtungsinstrumenten, wie das Cherenkov Telescope Array, erreicht werden.

This thesis considers the various morphologies of radio supernova remnants (SNRs), and attempts to determine whether their appearance results from the properties of the progenitor star and its supernova explosion, or from the structure of the interstellar medium (ISM) and ambient magnetic field into which a SNR consequently expands. High-resolution observations of Supernova 1987A show a young remnant whose appearance and evolution are completely dominated by the structure of its progenitor wind. A statistical study of the Galactic population of bilateral SNRs demonstrates that the symmetry axes of these remnants run parallel to the Galactic Plane. This result can be explained by the interaction of main sequence stellar wind-bubbles with the ambient magnetic field; expansion of SNRs into the resulting elongated cavities results in a bilateral appearance with the observed alignment. Radio observations of SNR G296.8-00.3 show a double-ringed morphology which is best explained by expansion either into an anisotropic main-sequence progenitor wind or into multiple cavities in the ISM. Data on SNRs G309.2-00.6 and G320.4-01.2 (MSH 15-52) make a strong case that the appearance of both remnants is significantly affected by collimated outflows from a central source; for G309.2-00.6 the source itself is not detected, but for G320.4-01.2 there is now compelling evidence that the remnant is associated with and is interacting with the young pulsar PSR B1509-58. I conclude that, while the youngest SNRs are shaped by their progenitor's circumstellar material, the appearance of most SNRs reflects the properties of the local ISM and magnetic field. Remnants which interact with an associated pulsar or binary system appear to be rare, and are easily distinguished by their unusual and distorted morphologies.

Thesis (Doctoral)--Technische Universität München, 1993. / "August 1993." Includes bibliographical references (p. 108-111).

We develop a simple one-zone model of the steady-state Crab nebula spectrum encompassing both the radio/soft X-ray and the GeV/multi-TeV observations. By solving the transport equation for GeV-TeV electrons injected at the wind termination shock as a log-parabola momentum distribution and evolved via energy losses, we determine analytically the resulting differential energy spectrum of photons. We find an impressive agreement with the observed spectrum of synchrotron emission, and the synchrotron self-Compton component reproduces the previously unexplained broad 200-GeV peak that matches the Fermi/Large Area Telescope (LAT) data beyond 1 GeV with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) data. We determine the parameters of the single log-parabola electron injection distribution, in contrast with multiple broken power-law electron spectra proposed in the literature. The resulting photon differential spectrum provides a natural interpretation of the deviation from power law customarily fitted with empirical multiple broken power laws. Our model can be applied to the radio-to-multi-TeV spectrum of a variety of astrophysical outflows, including pulsar wind nebulae and supernova remnants, as well as to interplanetary shocks.

A porção paulista do Vale do Ribeira concentra a maior quantidade de comunidades remanescentes de quilombos do estado de São Paulo, abrangendo uma área de cerca de 10% de seu território. Por meio das análises de marcadores moleculares, de frequências de casais com mesmo sobrenome e de dados genealógicos, procuramos obter parâmetros globais de caracterização das comunidades: sistema de cruzamentos e medidas de subestruturação populacional. Utilizamos dados genealógicos de cerca de 2000 indivíduos e moleculares de cerca de 1000 indivíduos das comunidades de Maria Rosa, Pilões, Galvão, São Pedro, Pedro Cubas, Ivaporanduva, Sapatu, André Lopes, Nhunguara, Abobral (margens esquerda e direita), Poça e Reginaldo. A estimativa média de F obtida pela análise de genealogias apresentou valor 0,00134, o qual, embora subestimado devido à falta de informações genealógicas, é cerca de 1,5 vezes mais elevado do que a estimativa apresentada para a população total brasileira e duas vezes maior que a obtida para o estado de São Paulo, comparando-se a valores apresentados em outros isolados da literatura. A partir das análises de locos genômicos obtivemos, para as comunidades separadamente, os valores médios de F relativos aos 239 locos de todas as comunidades, dentre os quais 12 (5%) mostraram-se estatisticamente diferentes de zero ao nível de P <= 0,05/n, frequência esperada de desvios ocorrendo ao acaso. Quando analisada de forma conjunta, a população apresentou quatro dos 30 locos (13,33%) com desvios significativos de pan-mixia, valor acima do esperado ao acaso, o que indica um excesso de homozigose no isolado total. Obtivemos o valor médio total de F pela ponderação dos F de cada um dos locos pelos recíprocos de suas variâncias, estas calculadas por meio de uma metodologia inédita proposta neste trabalho, a qual é aplicável a casos de marcadores contendo mais de dois alelos. O valor médio de F que obtivemos é comparável aos obtidos de outros isolados da literatura. Os valores do índice Fst obtidos em uma análise de subestruturação populacional tiveram valores modestos geralmente bem menores que 5%, indicando a presença de níveis de subestruturação muito modestos. / Vale do Ribeira is a region located at the southern part of the state of São Paulo, corresponding to about 10% of its territory. Most of the quilombo remnants of the state are placed inside this region. Using both molecular markers and genealogical data analyses, we estimated population genetic parameters from the communities (breeding system and subestructure organization). Genealogical and molecular data (collected from 2000 and 1000 individuals respectively) were obtained from 13 quilombo communities: Maria Rosa, Pilões, Galvão, São Pedro, Pedro Cubas, Ivaporanduva, Sapatu, André Lopes, Nhunguara, Abobral (both left and right edges), Poça e Reginaldo. Genealogical analysis enabled us to obtain a mean F value of 0.00134, that represents an underestimate of the true value due to lack of reliable genealogical information. Even so, this value is almost 1.5 times higher than the value estimated for the total Brazilian population and almost twice as high than the same parameter estimated for the state of São Paulo. By means of genomic loci data analysis, we obtained mean nF/n value for the quilombo communities separately. Twelve (5%) out of a total of 239 loci from eight communities were in p2:2pq:q2 ratios, as expected by chance; and for the set of all quilombo communities, four (13.33%) out of 30 loci deviated significantly from Hardy-Weinberg ratios, indicating an excess of homozygosis. We also estimated the weighted mean value of F for the whole population by averaging the nF/n values obtained from each locus by the reciprocal of their corresponding variances. For calculating the variance of estimated nF/n values we developed a novel method that can be easily generalized to the case of any number of alleles segregating at an autosomal locus/ No significant levels of population subtructure were detected since the estimated Fst values among populations were in general quite modest. We present also, as attachment to this work, the listings of the main computer program codes we used in our calculations and a section on the evolution of the fixation index F under different systems of regular endogamy.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23706号 / 理博第4796号 / 新制||理||1686(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)講師 LEE Shiu Hang, 教授 嶺重 慎, 准教授 前田 啓一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

1720 MHz OH masers have been detected towards a number of supernova remnants (SNRs) at the shock interface where the SNR slams into the interstellar medium. Models indicate that these masers are shock excited and can only be produced under tight constraints of the physical conditions. In particular, the masers can only form behind a C-type shock. Jets from newlyformed stars plow into the surrounding gas, creating nebulous regions known as Herbig Haro (HH) objects. Signatures of C-type shocks have been found in many HH objects. If conditions behind the shock fronts of HH objects are able to support 1720 MHz OH masers they would be a usefull diagnostic tool for star formation. A survey toward HH objects detected a number of 1720 MHz OH lines in emission, but future observations with arrays are required to confirm the presence of masers. / Physics / M.Sc. (Astronomy)

1720 MHz OH masers have been detected towards a number of supernova remnants (SNRs) at the shock interface where the SNR slams into the interstellar medium. Models indicate that these masers are shock excited and can only be produced under tight constraints of the physical conditions. In particular, the masers can only form behind a C-type shock. Jets from newlyformed stars plow into the surrounding gas, creating nebulous regions known as Herbig Haro (HH) objects. Signatures of C-type shocks have been found in many HH objects. If conditions behind the shock fronts of HH objects are able to support 1720 MHz OH masers they would be a usefull diagnostic tool for star formation. A survey toward HH objects detected a number of 1720 MHz OH lines in emission, but future observations with arrays are required to confirm the presence of masers. / Physics / M.Sc. (Astronomy)

We present a range of steady-state photoionization simulations, corresponding to different assumed shell geometries and compositions, of the unseen postulated rapidly expanding outer shell to the Crab Nebula. The properties of the shell are constrained by the mass that must lie within it, and by limits to the intensities of hydrogen recombination lines. In all cases the photoionization models predict very strong emission from high ionization lines that will not be emitted by the Crab’s filaments, alleviating problems with detecting these lines in the presence of light scattered from brighter parts of the Crab. The NIR [Ne VI] λ 7.652 mm line is a particularly good case; it should be dramatically brighter than the optical lines commonly used in searches. The C IV λ1549Å doublet is predicted to be the strongest absorption line from the shell, which is in agreement with HST observations. We show that the cooling timescale for the outer shell is much longer than the age of the Crab, due to the low density. This means that the temperature of the shell will actually “remember” its initial conditions. However, the recombination time is much shorter than the age of the Crab, so the predicted level of ionization should approximate the real ionization. In any case, it is clear that IR observations present the best opportunity to detect the outer shell and so guide future models that will constrain early events in the original explosion. Infrared observations have discovered a variety of objects, including filaments in the Crab Nebula and cool-core clusters of galaxies, where the H2 1-0 S(1) line is stronger than the infrared H I lines. A variety of processes could be responsible for this emission. Although many complete shock or PDR calculations of H2 emission have been published, we know of no previous simple calculation that shows the emission spectrum and level populations of thermally excited low-density H2. We present a range of purely thermal collisional simulations, corresponding to constant gas kinetic temperature at different densities. We consider the cases where the collisions affecting H2 are predominantly with atomic or molecular hydrogen. The resulting level population (often called “excitation”) diagrams show that excitation temperatures are sometimes lower than the gas kinetic temperature when the density is too low for the level populations to go to LTE. The atomic case goes to LTE at much lower densities than the molecular case due to larger collision rates. At low densities for the v=1 and 2 vibrational manifolds level populations are quasi-thermal, which could be misinterpreted as showing the gas is in LTE at high density. At low densities for the molecular case the level population diagrams are discontinuous between v=0 and 1 vibrational manifolds and between v=2, J=0, 1 and other higher J levels within the same vibrational manifold. These jumps could be used as density diagnostics. We show how much the H2 mass would be underestimated using the H2 1-0 S(1) line strength if the density is below that required for LTE. We give diagnostic diagrams showing level populations over a range of density and temperature. The density where the level populations are given by a Boltzmann distribution relative to the total molecular abundance (required to get the correct H2 mass), is shown for various cases. We discuss the implications of these results for the interpretation of H2 observations of the Crab Nebula and filaments in cool-core clusters of galaxies.