It has been shown that ionospheric irregularities can disturb our GNSS (Global Navigation Satellite System) communication. This disturbance is caused by scintillation of the radio signals when they pass through the ionosphere, leading to lock-on difficulties or in worst case, a loss of position for the GNSS-receiver. In this study, a large number of ground based GNSS reference stations spread across Sweden (known as the Swepos-network) was used to measure the variability of the GNSS-signal. These measurements were then combined with observations of ionospheric irregularities made by the Langmuir probes on ESA’s SWARM satellites. The study is a collaboration between Uppsala University and the Swedish Institute of Space Physics and covers five events between December 2013 to Mars 2021, when both datasets were available. The purpose is to determine the shape and extension of these ionospheric irregularities and how localized in time and space they are. The study also tries to answer whether it is possible to draw any conclusions regarding physical models such as diffraction or refraction from this comparison. It was found that during the event days, there was in general a clear increase (of often several hundred percent) of the spatial variability on different scales according to the standard deviation. This increase was seen for both the lower orbiting SWARM A and C satellites and the higher orbiting SWARM B. It was also possible to see that the increase of spatial variability was spread across all the studied latitudes, (magnetic latitude 49° to 70°). This corresponds well with the fact that all the analysed event days had an GNSS-signal variability above average for the same latitudes. There seems to be a clear connection between increased GNSS-signal variability and ionospheric irregularities, although more studies need to be done to be able to draw more accurate conclusions.

In this thesis, we investigate the interaction between electromagnetic, gravitational, and plasma related perturbations on homogeneous and hypersurface orthogonal Locally Rotationally Symmetric (LRS) class II spacetimes. By using these spacetimes, which allow for the inclusion of a non-zero magnetic field, as backgrounds in a perturbative approach, we are able to see interactions between the electromagnetic and gravitational variables already to first order in the perturbations. This is in contrast to earlier works using isotropic Friedmann-Lemaı̂tre-Robertson-Walker (FLRW) backgrounds, where one is usually faced with going to second order in the perturbations. To get the equations governing our perturbations, we use a 1+1+2 covariant approach and gather relations from the Ricci and Bianchi identities, Maxwell’s equations, particle conservation, and energy-momentum conservation for the individual plasma components. After linearising these equations around a LRS background, performing a harmonic decomposition, and using the Magnetohydrodynamic (MHD) approximation for a cold plasma, we then arrive at a closed system for the first order perturbations. This system, consisting of ordinary differential equations in time and a set of constraints, is then reduced to two separate subsectors, containing seven and nine variables respectively. These variables include quantities related to the Weyl tensor, the vorticity, and the electromagnetic fields, as well as perturbations in the plasma velocity and energy density. Through numerical calculations, we use the equations for these variables to show that perturbations in the magnetic field can be sourced by perturbations in both the plasma velocity and the gravitational variables. We also observe beat-like interference patterns for large values of the Alfvén velocity. These results can be of interest when considering the large scale cosmic magnetic fields, as their origin still seems to elude us. However, since we neglect thermal pressures and dissipative fluxes, it should be noted that our results are mainly applicable in the limit of low temperature and in cases where the thermal pressure is smaller than the pressure due to the electromagnetic fields.

The interaction of supernova (SN) ejecta with the circumstellar medium (CSM) drives a strong shock wave into the CSM. These shocks are ideal places where effective particle acceleration and magnetic field amplification can take place. The accelerated relativistic particles, in the presence of magnetic field, could emit a part of their energy via synchrotron radiation in radio wavelengths. The flux of this radiation, when compared with observations, gives an estimate of the CSM density. This could either be the particle density ($\rm n_{ISM}$) in case of the SN exploding in a constant density medium, characteristic of interstellar medium, or pre-SN mass loss rate ($\mdot$) of the progenitor system for a wind medium. In this work we have modeled the synchrotron luminosities and compared that with the radio upper limits measured for the Type Ia SNe 2011fe and 2014J. Assuming equipartition of energy between electric and magnetic fields, with 10$\%$ of the thermal shock energy in each field, we found a very low density medium, having $\rm n_{ISM} < \sim $ 0.35 $\ccc$,around both the SNe. In terms of $\mdot$ this implies an upper limit of $10^{-9}$ \msunyr for a wind velocity of 100 \kms. From the measurements of H I column density it could be expected that $\rm n_{ISM} \sim $ 1 $\ccc$ around both the SNe. If this is the true value close to the SNe, this would indicate that the energy density in magnetic field is less than that presumed for energy equipartition. The progenitors of both SNe 2011fe and 2014J are not clear. However previous studies have pointed toward a few potential  channels. Here, we have compared the CSM densities estimated by our models with that predicted by those different plausible formation channels and have tried to constrain the amplification of magnetic fields in SN shocks.

The cubic-kilometer sized IceCube neutrino observatory is burieddeep in the glacial ice at the Earth’s South Pole. Its low-energyextension array DeepCore enables physicists to search indirectlyfor light Dark Matter (DM) particles with masses as low as tensof GeV/c2 situated within our home galaxy, the Milky Way. GeVneutrinos could be produced through DM particle annihilations,propagating to the Earth where they could be detected by IceCube. This licentiate thesis presents a search for Weakly Interacting Mas-sive Particles (WIMPs) with masses as low as 30 GeV/c2 in theGalactic center (GC) using the 79-string configuration of the IceCubeneutrino detector. Data from 319.7 live-days have been analyzedusing a cut-and-count analysis approach, and found to be consistentwith the background-only hypothesis with expected backgroundfrom atmospheric muons and neutrinos. Thus, upper limits wereset on the velocity averaged DM annihilation cross-section. The Precision IceCube Next Generation Upgrade (PINGU) as apossible future neutrino detector within DeepCore would reducethe neutrino energy detection threshold to a few GeV. In additionto the data analysis with DeepCore, a sensitivity study has beenconducted to investigate the performance of PINGU for indirectDM searches in the GC and the Sun. In the Sun WIMPs could begravitationally captured through elastic scattering off nucleons. Inthis thesis, we derive PINGU sensitivities for the velocity averagedDM annihilation cross-section of WIMPs in the GC, and for theSpin-Dependent (SD) and Spin-Independent (SI) WIMP-protonscattering cross-sections, under the assumption of thermodynamicequilibrium between the WIMP capturing and annihilation rate inthe Sun. / IceCube

In the year 2011 the construction of IceCube, a neutrino observatory buried in deep clear Antarctic ice, was completed. IceCube now consists of an array of 5160 digital light detection modules assembled on 86 strings, which encloses a instrumented volume of roughly 1~km$^3$ optimized for detection of neutrinos down to energies of 100~GeV. In this detector eight of these strings are arranged in a denser configuration of the low energy extension DeepCore, which pushes the neutrino energy threshold further down to 10~GeV.\\This allows probing for fluxes from various astrophysical sources. Of special interest in context of Dark Matter theories is the Sun as a potential source of energetic neutrinos. There neutrinos can be messenger particles created in annihilations of trapped Dark Matter particles (WIMPs). Searches for solar WIMPs have a tradition in IceCube and shall be continued with data recorded in the completed detector configuration (IC86). Since the detector configuration does not substantially change further, it is worthwhile to revisit, investigate and refine analysis methods developed during the construction phases and improve on them.\\Described in this thesis is the preparation work for such an improved analysis: filter and data treatment studies have been conducted during three years ensuring the quality of the experimental data stream. In parallel the simulation codes 'WimpSim' and 'WimpSim-Reader' have been improved, which provide the signal definition for solar WIMP studies. Also in an extensive investigation about event splitting and hit clustering algorithms has been conducted. This yielded an alternative event splitting and recombination approach using 'MaxDist-Splitter' and 'CoincidentSuite'. In a subsequent study it could be shown that thereby the performance was increased compared to previous solutions by up to 50\%. Also the general benefit of these alternative solutions for general data processing has been investigated, which can remedy so far unregarded problems in lowest level data treatment. Furthermore the analysis strategy has been reviewed and adjusted to the new conditions, which is expected to bring furtherimprovements.\\By this work the foundation for the next solar WIMP analysis has been laid and the achieved improvements are expected to improve the sensitivity. / <p>I like Cats</p> / IceCube

The main mission of the JEM-EUSO (Extreme Universe Space Observatory) Collaborationis to observe Cosmic Rays. These high energy particles come from a variety of sources and bombard the Earth all the time. However, the higher the energy, the lower the flux, and particles with an energy above 1018eV (called Ultra High Energy Cosmic Rays or UHECRs) are so sparse that just a few might hit the atmosphere in a year. When CRs, and UHECRs, hit the atmosphere they cause what is called Extensive Air Showers, EAS, a cascade of secondary particles. This limits the effectiveness of ground based observatories, and that is where theJEM-EUSO Collaboration comes in. The goal is to measure UHECRs, by observing the fluorescence of the EAS from space. This way huge areas of the atmosphere can be covered and both galactic hemispheres can be studied. Since the JEM-EUSO instruments are telescopes measuring in the near UV range, a lot of other phenomena can be observed. One of these applications is UV nightglow. Airglow in general are lights in the sky which are emitted from the atmosphere itself, while nightglow is simply the nighttime airglow. There are many uses of airglow, and one of these is as a medium to observe atmospheric gravity waves. The aim of this thesis is to investigate how a space-based photon counting telescope, such as those of the JEM-EUSO Collaboration, can be used to measure disturbances in the terrestrial nightglow, to identify atmospheric gravity waves. To accomplish this, a theoretical basis for these interactions was explored and a simple scenario was built to explore the plausibility of measuring UV nightglow modulations. The aim was to see what variables would affect a measurement, and how important they were. Along side this, a calibration was conducted on one of the JEM-EUSO Collaborations instruments, the EUSO-TA (EUSO-Telescope Array). The goal in the end was to try and measurethe night sky, to complement the calculations. The investigation showed that the conditions during the measurement are very important to the measurement. This includes things like background intensity, nightglow activity, and magnitude/shape of the modulations. Of more importance though are the parameters which can be actively changed to improve the measurement, the most important of which is measurement time. It was concluded that a measurement of the nightglow modulation should be, under the right conditions, possible to do with a currently operating instrument, the Mini-EUSO, or similar instrument. The calibration of the EUSO-TA involved a series of repairs and tests, which highlighted some strengths and weaknesses of the instrument. However, the calibration itself produced few workable results that in the best case scenario reduced the focal surface to an unevenly biased 2-by-2 Elementary Cell square. Unfortunately this would not be sufficient to do proper measurements with, but the process did point out shortcomings with the then involved sensors, as well as some problematic aspects of the software operating the instrument.

This thesis treats the findings and current theories of the active galactic nuclei 3454.3. It mainly aims to describe the behavior of the specific source in the gamma-ray energy band as recorded by the Fermi-LAT satellite. Using NASA’s computational tools and all recorded data the variability of the source was assessed. As the received flux from the source varies substantially over time several periods of time for which the flux differs considerably were analysed. Spectral analysis for the various time-frames was performed in order to determine how we best can describe the results from each period. The Fermi-LAT results were then examined in the wider context of multi-wavelength astronomy. Finally, data retrieved at all wavelengths were modeled and compared in accordance with currently held theories.

As a result of the standardizability of SNe Ia light curves over a wide range of photometric bands, they are used as standard candles to accurately measure distances in the cosmos up to z ≈ 1 [22]. As dust extinction is smaller in the NIR than in the optical [21] there is less dispersion seen in the peak brightnesses of SNe Ia, making them truly standard candles. We use SNPY to fit light curves for 192 SNe Ia. The mean of all Hubble residuals of our sample is ≈ 0.101 mag with a standard deviation of ≈ 0.234 mag. After applying an original set of cuts, the mean of 173 Hubble residuals reduces to ≈ 0.080 mag with a standard deviation of 0.203 mag. We next estimate host galaxy stellar masses of 175 SNe. From our sample we detect a 0.039 ± 0.026 mag (1−2σ) mass-step. For reasons outlined in section 4.1.1 and 4.1.2 respectively, we increase our sBV cut to sBV &gt; 0.8 and decrease our extinction cut to E(B −V ) ≤ 0.2 mag to see the mass step disappear entirely (0.004 ± 0.034 mag). Fast-declining SNe occur with preference in high-mass galaxies, possibly pointing to an intrinsic contribution to this mass step [22]. As NIR data is seen to significantly reduce the 3−4σ [14] mass-step detected with optical data, it is concluded that extinction likely plays a large role in the mass-step, as proposed in Brout &amp; Scolnic 2020 [2]. / <p>Presentation given over zoom due to the COVID-19 crisis.</p>

The search for extrasolar planets had been ongoing for many years when Mayorand Queloz discovered 51 Pegasi b in 1995. It was a giant gas planet similar to Jupiter, but with a larger radius and of only half of Jupiter’s mass. Theso called Hot Jupiter was observed to orbit its host star 7 times closer thanMercury is orbiting the Sun. Theoretical models at the time stated that gasgiants could not form in such a short distance to the host star. Thus, thisdiscovery was completely unexpected. It was the beginning of a new field ofresearch where the diversity of exoplanets is the most remarkable discovery, challenging theoretical models. Thanks to the Kepler space telescope and anew generation of space missions such as TESS, thousands of exoplanets havebeen discovered and thousands of planet candidates await confirmation. In this thesis I have studied all confirmed exoplanets to this date, which havebeen discovered by the radial velocity and/or the transit method. The planetparameters and their stellar hosts are available on NASA’s Exoplanet Archive.For all planets &lt; 100 M⊕, I have assessed and updated the parameters for eachplanet in particular when several solutions exist. There are several types ofplanets, but the focus of this work are small planets which come in two sizes: Rocky super-Earths, and the slightly larger and lower density sub-Neptune. Different types of planets have different radii and mass ranges, which togetherwith composition and interior structure are separating the types from each other. These mass and radii ranges are however not universally defined, and in thisreport the super-Earth and sub-Neptune ranges are discussed together with their typical characteristics. The radii and mass ranges of the two different classes of small planets are overlapping and are often difficult to classify. In particularfor planets in between 2 R⊕ and 3 R⊕, there is an ambiguity of structure and composition. This report will also investigate how planet properties depend on the stellarhost properties and on the orbital distances to the stars. One of my mainresults is that sub-Neptunes are common orbiting host stars with low metallicity, in contrast to super-Earths which are common orbiting host stars with highmetallicity. Other parameters, such as stellar effective temperature, seem to have no influence on planet properties. Super-Earth’s are found at a wide range of orbital distances while the sub-Neptunes cluster in a narrow range of orbital distances to their host star. Sub-Neptunes have an atmosphere, and are orbiting at distances where the atmosphere does not evaporate from intense host star radiation. If an atmospheree vaporates, only the rocky core of the planet is left. Thus, some super-Earths might have been sub-Neptunes that have lost their atmospheres. My second main result is that planets with characteristics of sub-Neptunes (with respect to density and interior structure) of 10 M⊕ to 15 M⊕ have radiibetween 2 R⊕ and 4.5 R⊕. Sub-Neptunes in the upper mass limit, between 15M⊕ to 17 M⊕, have radii from 2.6 R⊕ to 7.5 R⊕. And finally, my third result is the relation between planet density and equilibrium temperature. The density of all planets with masses &lt; 15 M⊕ is Earth-like for equilibrium temperatures &gt; 1400 K. For lower equilibrium temperatures corresponding to longer orbital periods, or lower-mass and cooler stars, planetswith masses &lt; 15 M⊕ have a larger spread in densities. However, it never fallsbelow a diagonal linear trend in the density against equilibrium temperature diagram described by ρ = 2.6 × log10(Teq) − 7.46.

The  rst stars to illuminate the universe are said to belong to a group called Population III. Having knowledge of their atmospheric conditions would be useful in many endeavours. The aimof this project was to compile and run the FORTRAN code TLUSTY (Hubeny and Lanz 2017) inorder to create stellar atmospheres for Pop III stars. With a working version of TLUSTY, severalcontrol runs were then performed to make sure that everything worked as intended with the  final goal to create a large grid of calculated atmospheres in the parameter space of effective temperatureand surface gravity. Successful comparisons were made against earlier calculations made by Schaerer(2002) and Windhorst et al. (2019). Constructing such a grid required several codes to work togetherwith TLUSTY by constructing a shell script. The result is a grid  lled with many points that werewell converged, as well as a few that did not appear to converge. Comparing the converged part ofthe grid with stellar evaluations tracks made by Yoon et al. (2012) showed that heavy, rotating PopIII stars fell almost within the grid. One problem that arose, however, was that as the grid did notfully converge all the way to the tracks some could not be uniquely mapped to di erent points on thegrid. Thus, some di erent tracks would become degenerate which should not be physically expected. However this may not be a fatal problem.