京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20900号 / 理博第4352号 / 新制||理||1625(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)教授 田中 貴浩, 教授 向山 信治, 教授 川合 光 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Supernova remnants (SNRs) are the end products of supernova (SN) explosions. These explosions happen when certain massive stars face the ends of their evolutionary cycle and create shock waves propagating in the surrounding medium by ejecting part of the star’s material. An SNR is the region defined by these powerful shocks. Due to the nature of SNRs spreading stellar material to their surroundings, they play a major part in the chemical evolution of the universe.  Some SNRs are observed to contain a pulsar (PSR), a spinning neutron star emitting electromagnetic radiation through its magnetic poles, and a pulsar-wind nebula (PWN), where relativistic particles and magnetic fields escaping the pulsar interact with the surroundings. This is the case for SNR 0540-69.3 (SNR0540), the so called twin of one of the most studied astronomical objects in the sky, the Crab Nebula. The attached paper (Paper I) is based on VLT observations of the central regions of SNR 0540 with the instruments MUSE and X-Shooter. The MUSE observations provide a possibility to study the optical spatial variations of SNR 0540 for the first time utilising spectroscopy, and are in general one of the few such studies of PWNe in the optical. On the other hand, earlier works focusing on the shape of the SNR 0540 continuum spectrum in the optical wavelengths have mostly utilised narrow band photometry, which has yielded conflicting results. The X-shooter observations of SNR 0540 providing the first near-infrared (NIR) spectrum with a good coverage in the optical can be used to tackle these problems.  In Paper I, the continuum emission is modelled by power-law models to constrain the underlying conditions in the PSR and PWN in SNR 0540. An important parameter in these models is called the spectral index (α), which determines the slope of the spectrum. We find significant spatial variations in the spectral index that reveal a torus-jet structure around the PSR, confirming earlier results. Surprisingly, we also find that the spectral index decreases (from α ~ 1.7 to α ~ 0.5) toward the outer parts of the PWN and is the largest for the PSR (α1 ~ 1 in the low and α2 ~ 2 in the high frequencies), in contrast to theoretical expectations for the basic scenario of synchrotron cooling. Additionally, two spectral indices seem to be required to characterise both the PSR’s and PWN’s optical(-NIR) spectra.  Future observations in the optical but also in the infrared and X-rays would help understanding the complex conditions in the central regions of SNRs. Most importantly, optical observations of other SNRs would shed light on whether SNR 0540 is a special case. The unexpected spectral index variations in SNR 0540 highlight the need for further theoretical work to better understand the origin of the optical synchrotron emission in PSRs and PWNe. / Supernovarester (SNR) är slutprodukterna av supernovaexplosioner (SN). Dessa explosioner inträffar när vissa massiva stjärnor möter ändarna av sin evolutionära cykel och skapar chockvågor som fortplantar sig i det omgivande mediet genom att stöta ut en del av stjärnans material. En SNR är regionen som definieras av dessa kraftfulla stötar. På grund av naturen hos SNR som sprider stjärnmaterial till sin omgivning spelar de en stor roll i universums kemiska utveckling.  Vissa SNR:er har observerats innehålla en pulsar (PSR), en snurrande neutronstjärna som sänder ut elektromagnetisk strålning genom sina magnetiska poler, och en pulsar-vindnebulosa (PWN), där relativistiska partiklar och magnetfält som flyr pulsarn interagerar med omgivningen. Detta är fallet för SNR 0540-69.3 (SNR 0540), den så kallade tvillingen till ett av de mest studerade astronomiska objekten på himlen, Krabbanebulosan. Bifogade papper (Paper I) är baserad på VLT-observationer av de centrala regionerna i SNR 0540 med instrumenten MUSE och X-Shooter. MUSE-observationerna ger en möjlighet att studera de optiska rumsliga variationerna av SNR 0540 för första gången med hjälp av spektroskopi, och är i allmänhet en av få sådana studier av PWNe i optiken. A andra sidan har tidigare arbeten med fokus på formen av SNR 0540-kontinuumspektrumet i de optiska våglängderna mestadels använt smalbandsfotometri, vilket har gett motstridiga resultat. X-shooter-observationerna av SNR 0540 som ger det första nära-infraröda (NIR) spektrumet med en bra täckning i optiken kan användas för att ta itu med dessa problem.  I Paper I modelleras synkrotronemissionen av potenslagsmodeller för att begränsa de underliggande förhållandena i PSR och PWN i SNR 0540. En viktig parameter i dessa modeller kallas spektralindex (α), som bestämmer spektrumets lutning. Vi hittar betydande rumsliga variationer i det spektrala indexet som avslöjar en torus-jet-struktur runt PSR, vilket bekraftar tidigare resultat. Överraskande nog finner vi också att spektralindexet minskar (från α ~ 1.7 till α ~ 0.5) mot de yttre delarna av PWN och är störst för PSR (α1 ~ 1 i de låga och α2 ~ 2 i de höga frekvenserna), i motsats till teoretiska förväntningar på grundscenariot med synkrotronkylning. Dessutom verkar två spektrala index krävas för att karakterisera både PSR:s och PWN:s optiska(-NIR) spektra.  Framtida observationer inom det optiska, men också i det infraröda och röntgenstrålar skulle hjälpa till att förstå de komplexa förhållandena i de centrala regionerna av SNR. Det viktigaste är att optiska observationer av andra SNR:er skulle belysa om SNR 0540 är ett specialfall. De oväntade spektrala indexvariationerna i SNR 0540 belyser behovet av ytterligare teoretiskt arbete för att bättre förstå ursprunget till den optiska synkrotronemissionen i PSR och PWNe. / <p>QC 2023-05-23</p>

In this report calibration of the four probes attached onto the JUICE spacecraft has been made.The JUICE spacecraft (JUpiter Icy Moon Explorer) is a spacecraft which will investigate theenvironment on and around Jupiter and its four biggest moons. On the spacecraft are 10different instruments onboard, where one of the instruments is the Radio and Plasma WaveInvestigator (RPWI). The mission of RPWI is to measure the electromagnetic field and plasmaparticles, among other things around the Jovian system. To analyse the measured data fromthe probe, the data has to be calibrated. In this report test data and raw flight data of the probeshas been calibrated by digital-analog converting the signal. The data SID 1 and SID 3, whichboth measure the electric field, the calibration was successful both for the ground test data andthe raw flight data. However, the calibration of SID 2, which measure the plasma density, didnot give the calibrated analog signal within expected range. Possible sources of error for thatdeviation includes error in the Fourier Transform of the transfer function. The raw flight data forSID 1 and 2 was further disturbed by solar wind, resulting in high measured signals for theelectric field and the plasma density. For future improvements this calibration method could berepeated on another set of data without disturbance to verify the calibration method and identifypotential source of error.

No description available.

In this report, we constrain properties of foreground objects in the Milky Way that have the potential of being confused with accretion disks of Population III stellar- mass black holes at high redshift. Following Windhorst et al. (2018), a model for multicolour accretion disks of Population III stellar-mass black holes is presented. The resulting spectra are used to derive observable magnitudes with the James Webb Space Telescope (JWST). Magnification of a factor 103 to 106, depending on the black hole mass, through gravitational lensing is necessary to surpass the JWST detection limit. Spectra of faint Milky Way objects of low-mass main sequence or pre-main sequence stars (Baraffe et al. 2015) and cool brown dwarfs and giant exoplanets (Phillips et al. 2020) were fitted to a distance such that their observable JWST magnitudes are similar to those of the accretion disk. We find that the spectral energy distributions that have the highest chances of being confused with high redshift Population III black hole accretion disks belong to pre-main sequence and low-mass main sequence stars of temperature 1500 K to 4200 K. At redshift 𝑧 = 7, accretion disks most closely resemble the spectral energy distributions of 2830 K Milky Way objects. Cool brown dwarfs or giant exoplanets with chemical equilibrium atmospheres at temperature ∼ 2700 K or chemical non-equilibrium atmospheres at ∼ 1790 K most closely resemble the spectral energy distribution of redshift 𝑧 = 7–8. Although the SEDs produce good fits, a confusion probability can sometimes be reduced because the models are very young (0.5 to 10 Myr) or have distances corresponding to the stellar halo (≳ 200 kpc).

Abstract Not Provided / Thesis / Master of Arts (MA)

In this project, we investigate the plasma heating associated with coherent structures, such as current sheets and vortices, in different solar wind conditions: slow solar wind, stream interaction regions, and heliospheric current sheets, observed by the Solar Or- biter mission. To unravel this mystery, we first use the Partial Variance of Increment method [1] to locate these coherent structures. We then employ correlation functions to determine the coexistence of these structures and investigate the global elevation of plasma temperature [2]. Additionally, we employ a quantitative analysis of conditioned PVI [3] to examine the local increase in plasma temperature [4]. The results clearly indicate that plasma heating takes place at and near these struc- tures. Specifically, current sheets locally heat the plasma, while plasma vortices have a global impact on heating. A characteristic timescale of approximately 200 seconds emerges, separating the local heating of coherent structures from other heating sources. In slow solar wind and stream interaction regions, we observe clusters of coherent structures with sizes ranging from 4 to 6 hours, underlain by a scale of 1 to 2 hours. The heliospheric current sheet does not exhibit such modulation. These coherent struc- ture clusters are embedded within larger macroscopic structures spanning 12 to 24 hours.

In this thesis, we study slowly rotating relativistic stars by modeling them as perfect fluids. The Hartle formalism is used to perturb a spherically symmetric static solution into slow rotation and the corresponding field equations to second order are presented. Five of the seven equations form a subsystem that decouples and can thus be solved independently. It is solely this system we focus on in this work. Two new variables are introduced to rewrite the field equations such that they become algebraic in one of the variables, the other one is used as a generating function and can be chosen to generate desired perfect fluid configurations. To adapt for numerical integration, the field equations are further reformulated as a coupled system of ordinary differential equations, which is solved numerically using a fourth order Runge-Kutta method. Two choices of the generating function are examined, namely a simple polynomial case as well as the Kuch2 III solution, and the related field equations are solved to find the perturbative functions. By studying physical quantities such as the pressure, energy density and speed of sound to zeroth order, we show that both of the studied configurations correspond to physically realistic solutions within a range of parameter values. Additionally, the shape of the zero pressure surface to second order is analyzed and found to be oblate for both cases, which coincides with the expected shape of a rotating fluid. We also investigate whether the Petrov type D condition is fulfilled, and the results indicate that both solutions fail to satisfy the condition and are thus not of Petrov type D. Moreover, it is shown that both the polynomial case and the perturbed Kuch2 III solution can be matched to a suitable asymptotically flat vacuum exterior, using the Darmois-Israel procedure. It should be noted that even though we are solely examining the slowly rotating limit, our results are in fact valid even up to fairly high rotational velocities. This indicates that the perturbative generating method of this thesis may be used to produce models describing physically reasonable configurations, e.g. rotating neutron stars.

No description available.

This thesis introduces briefly physical processes operating in the ISM around massive starsand focuses on the impact strong stellar feedback has in creating large-scale structures in a galaxy.Stellar feedback is ubiquitous in star forming galaxies and its effect on the ISM depends strongly on the energy output from the most massive stars (M$\geq$7 \Mo ) and the properties of the surrounding gas. Starburst galaxies are among the most active in producing %galaxies are among the most active galaxies and produce a large amount of massive star clusters %or even super star clusters (SSC; M$_{cl} \geq 10^5$ \Mo ), with stellar populations up to thousands of massive stars. %The most massive stars (M$\geq$30 \Mo ) are lives short, but they In the first 4 Myr of the star clusters evolution, radiative feedback of the most massive stars (M$\geq$30 \Mo ) are at work. Large amount of ionizing photons are released to the ambient medium while radiative pressure compress the surrounding gas. At the same time their stellar winds inject continuously mechanical energy and momentum in their surrounding. This mechanical feedback is then at later ages, until $\sim$ 40 Myrs, maintained by supernova explosions from the less massive stars. Strong stellar feedback tends to develop large-scale structures such as bubbles, loops, filaments and outflows. These are transient structures and can be seen as imprints of how the released energy is clearing or has cleared paths in the ISM. Strong stellar feedback can have devastating consequences in dwarf galaxies due to their shallow gravitational potential. It can accelerate outflows with velocities larger than their escape velocities. In this way, dwarf galaxies can lose a large fraction of their gas mass, which will be crucial in their subsequent evolution.On the other hand, galactic winds might be responsible to create holes in the ISM, allowing the easily-absorbed ionizing photons (Lyman continuum photons, LyC) to escape the galaxy. Studies on a few LyC leaking galaxies have shown that this mechanisms might have preference from a density-bound scenario, which takes place in galaxies with a highly ionized halo. In my paper I used deep MUSE observations to analyse the impact strong stellar feedback has in the starburst and Lyman continuum emitting galaxy: Haro 11. The paper presents three emission line diagnostics aiming to analyse the condition of the warm ionized gas in this galaxy, which are the \Ha\ emission, the level of ionization in gas and the presence of fast shocks. These diagnostics are presented in maps of 50 \kms\ bins in a velocity range from -400 to 350 \kms . Haro 11 shows a violent ISM whose warm ionized gas is almost completely shaped by effect of stellar feedback from the most massive star forming regions in the centre. Arcs, shells, outflows paths and galactic scale ionizing cones are imprinted in ISM of Haro 11. Our analysis suggests the presence of a kpc-scale superbubble which might have created galactic holes in the ISM. Beside of that, Haro 11 shows a highly ionized halo. Both mechanisms appear to facilitate the escape of LyC in this galaxy. %Finally, we observe emission at velocities up to thousand \kms\ which could hints to gas escaping the galaxy. Finally the paper presents estimates of the gas mass fraction that could escape the gravitational potential of the galaxy.