Gamma-ray bursts (GRBs) are some of the most energetic events in the universe. Shocks occurring below the photosphere are likely radiation mediated shocks (RMSs) and are suspected to shape the spectra. Due to computational costs of simulating RMSs, models had not been fitted to data and a faster model was needed. The Kompaneets RMS Approximation (KRA) is an analog model of RMSs, creating spectra which are identical to full RMS simulation spectra and it is significantly faster. For a sample of short GRBs I found that spectra are very hard and close to a non-dissipative photosphere (NDP). Therefore any trace of energy dissipation is lost to thermalization and many KRA solutions are possible with statistics similar to the Band model. A sample of long GRBs have typical spectra, i.e. spectra much broader than a blackbody (BB) and the KRA can model these spectra very well. Statistically, KRA is as good as the Band model and significantly better for GRB211211. I also found two spectral shapes describing observed data equally well. First, a broadened BB for a steady-state outflow, and secondly, optically shallow shocks for a non steady-state outflow. To distinguish between these solutions, upcoming detectors with lower-energy data are important. In conclusion, the KRA can reproduce photospheric spectra altered by a RMS, and these spectra can explain observed GRB spectra. If the spectrum is not thermalized, information about the properties of the shock can be deduced from observed GRB spectra. / Gamma-blixtar är några av de mest energirika händelserna i universum. Chocker som uppkommer under fotosfären är troligtvis strålnings medlade chocker (RMSer) och misstänks forma spektra. Höga beräkningsmässiga kostnader för simuleringar av RMSer har lett till att modeller inte har anpassats till data. The Kompaneets RMS Approximation (KRA) är en analog modell av RMSer som skapar identiska spektra och är mycket snabbare. För ett urval av korta gamma-blixtar hittar jag väldigt hårda spektra, nära en icke-dissiperad fotosfär (NDP). Alla spår av dissipering har därför försvunnit p.g.a. termaliseringen och många olika KRA lösningar kan anpassa dessa spektra lika bra som Band modellen. Ett urval av långa gamma-blixtar har typiska spektra, d.v.s. spektra mycket bredare än svartkropp spektra och KRA kan anpassa dessa spektra väldigt bra. Statistiskt är KRA lika bra som Band modellen och t.o.m. mycket bättre för GRB211211. Jag har också hittat två olika former på spektra som anpassar data lika bra. Först, en breddad svartkropp för ett utflöde i jämvikt och den andra, optiskt grunda shocker för ett utflöde som inte är i jämvikt. För att urskilja mellan dessa lösningar är framtida detektorer med data för lägre energies viktiga. För att sammanfatta, KRA kan reproducera fotosfäriska spektra påverkade av en RMS och dessa spektra can förklara observerade gamma-blixt spektra. Om spektrumet inte är termaliserat kan information om chockens egenskaper hämtas från observerade gamma-blixt spektra.

Three-dimensional (3D) planetary general circulation models (GCMs) have been derived from global climate models used to project 21st century changes in Earth's climate. GCMs are used to address questions regarding the climate-and habitability aspects of terrestrial planets within the solar system and assess the habitability of planets outside of the solar system, so called exoplanets. The development of GCMs has given rise to various results for concepts essential for determining potential habitable exoplanets such as the Habitable zone, hence intercomparison studies are of interest. In this project, the climate of an exoplanet with a static thermodynamic ocean will be modelled using ROCKE-3D, an open-source (3D) GCM developed at the NASA Goddard Institute for Space Studies. This is done in order to simulate the climate and examine how the simulations compare to other GCMs. The climate simulation will also be applied to an Earth-like planet in order to determine how an Earth-like climate will impact the results. We find that the climate on a rapidly rotating Aquaplanet receiving a G-star spectral energy distribution is surprisingly Earth-like. By contributing to a higher albedo, the ocean ice fraction of a rapidly rotating Aquaplanet was shown to impact the temperature and humidity structure considerably, despite the absence of Ocean Heat Transport. However, small differences between the simulations with and without sea ice were found for a tidally locked Aquaplanet receiving a M-star spectral energy distribution, which indicates that ROCKE-3D is not shutting off sea ice properly. Generally, ROCKE-3D shows similar results as CAM4 for the G-star runs and for the M-star, ROCKE-3D shows similar results to LMDG. / Tredimensionella (3D) planetariska allmänna cirkulationsmodeller (GCM) har härletts från de globala klimatmodeller som används för att projicera 2000-talets förändringar i jordens klimat. GCM används för att bemöta frågor om klimat- och beboelighetsaspekter av jordlika planeter inom solsystemet och bedöma beboeligheten för planeter utanför solsystemet, så kallade exoplaneter. Utvecklingen av GCM har gett upphov till olika resultat för begrepp som är väsentliga för att bestämma potentiella beboeliga exoplaneter såsom den beboerliga zonen, därför är jämförande studier av intresse. I detta projekt kommer klimatet för en exoplanet med ett statiskt termodynamiskt hav att modelleras av ROCKE-3D, en öppen källkod (3D) GCM utvecklad vid NASA Goddard Institute for Space Studies. Detta görs för att simulera klimatet och undersöka hur simuleringarna står sig i jämförelse med andra GCMs. Klimatsimuleringen kommer också att tillämpas på en jordliknande planet för att avgöra hur ett jordliknande klimat kommer att påverka resultaten. Vi finner att klimatet på en snabbt roterande vattenplanet som mottar en G-stjärnig spektral energifördelning är överraskande jordliknande. Genom att bidra till ett högre albedo visade havsisfraktionen av en snabbt roterande Aquaplanet att påverka temperatur- och fuktstrukturen avsevärt, trots frånvaron av havsvärmetransport. Små skillnader mellan simuleringarna med-och utan havsis påvisades för en tidvattenlåst vattenplanet som mottar en M-stjärnig spektral energifördelning, vilket tyder på att ROCKE-3D inte bortser havsis ordentligt. Generellt visar ROCKE-3D liknande resultat som CAM4 för en G-stjärna. För en M-stjärna visar ROCKE-3D liknande resultat som LMDG.

At higher redshift galaxies exhibit increasingly irregular and clumpy morphologies, withstar-forming clumps dominating the FUV output of their host galaxies thus being inti-mately related to star formation and the formation and evolution of galaxies. This workexamines star-forming clumps in a remarkable, young spiral galaxy at Cosmic Noon witha redshift ofz= 2.584, lensed by the galaxy cluster Abell 2744. To this aim, NIRCamobservations in 7 filter bands are utilized to determine photometry of clumps and performbroadband SED fitting to determine characteristic sizes, ages and masses and infer theirdynamical ages and mass surface densities. The clump within this galaxy spans a widerange of properties with sizes between 20 to 200 pc and masses between 105M⊙and109M⊙. While clumps are not resolved down to scales of individual star clusters, small,dense clumps may host star clusters. A number of clumps exhibits agestage>100 Myr,thus being able to survive feedback up to these timescales. This population of clumpsalso appears to be dynamically evolved and gravitationally bound as well as the denseststructures within the investigated sample, with roughly∼20% of clumps exhibiting masssurface densities comparable to bound stellar clusters in the local Universe.

No description available.

The first billion years from the beginning of the Universe is the focus of multiple astronomical facilities in the upcoming decade. This unique era is marked by the formation of the first stars and galaxies, which release ionising radiation into the intergalactic medium(IGM). As a result, these sources initiate a period during which the cold and dense IGM, primarily consisting of neutral hydrogen (HI ), is heated and ionised. We refer to this era as the Epoch of Reionisation (EoR). How the EoR transpired hence depends on the properties of these ionising sources, and this forms a vital piece to the puzzle of understanding the early Universe. This licentiate thesis aims to educate the reader on the power spectrum (PS) statistic of the 21-cm signal from HI during the EoR. The PS is a prospective observable by radio interferometers, such as the Low-Frequency Array (LOFAR) and the future Square Kilometre Array (SKA). It is an essential stepping stone in comprehending the dominant physical processes affecting the IGM at a given length scale during the EoR. In Paper I, we analyse the decomposition of the 21-cm PS from Lidz et al. (2007) (eq. 2)and study the evolution of its terms. We conduct our investigation for a set of C 2 -Ray and 21cmFAST simulations with volumes of (714 cMpc)3, concentrating on large-scales (k < 0.3 Mpc−1 ) as the signal-to-noise ratio of observing these scales will be high. We find that the 21-cm PS tracks the PS of neutral hydrogen fluctuations, which itself past a certain scale tracks the matter PS after a global ionisation fraction of x̄HII∼ 0.1. Hence, the 21-cm PS possesses a two-regime form for which the large-scale PS is a biased version of the cosmological density field and the small-scale PS depends on the astrophysics of the EoR. We construct a bias parameter to explore whether the 21-cm PS can be used as a probe of cosmology on large k-scales. We discover a transition feature for both simulations, following the ktrans ≈ 2/λMFP empirical formula. The transition scale between the scale-independent and scale-dependent bias regimes is directly related to the value of the mean free path of ionising photons (λMFP ).

This paper uses the Pantheon+ data set that consists of 1701 light curves of 1550 unique type IaSupernova to find constraints on various cosmological models and compare them with a varying darkenergy model proposed by Chevallier, Polarski and Linder in the early 2000s and analyze it deeper.The results show a tipping point from a decelerating universe to an accelerating one at a redshift ofz = 0.35, and a second tipping point back to a decelerating universe in the future at z = −0.19. The flatChevallier-Polarski-Linder (CPL) model leads to a matter dominated universe with Ωm = 0.52 ± 0.08while the relative dark energy density Ωde = 0.48±0.08. Finally, taking all these models and comparingthem with the results that are found from Taylor expanding the distance relation shows that they aremostly consistent with a deceleration parameter around q0 = −0.28.

This work is a preliminary study of the background of a search for dark, long-lived particles in the IceCube detector. The high flux of atmospheric muons in IceCube is considered background to the detector's primary science goal, which is to detect astrophysical neutrinos through the emission of Cherenkov radiation. However, high muon rates may break fresh ground for the detection of hypothetical dark particles. These could be created during the Bremsstrahlung-like interaction of an energetic muon and decay into a muon and an electron. Such an event is expected to produce a characteristic signal in the detector: A track-like signal produced by the Cherenkov-photon emitting muon, followed by a gap due to the electric neutrality of the dark particle. The subsequent decay of the dark particle into a muon produces a further track-like signal. In order to probe the success rate of this endeavor, two precursory statistical analyses are made using simulated data provided by CORSIKA. In order to obtain a clear track-gap signature that is not diluted by other particles, atmospheric muons should preferably travel in a bundle of few to no other muons. The muon multiplicity in incident bundles is estimated. The study reveals that 50% of all muons are single muons at the point of production, while their relative number increases to 70% by the time they reach the detector boundary. A possible background to this search is assumed to be produced by a collinear neutrino interacting after a stop of the muon. The muon may stop due to energy loss or spontaneous decay. In that case, the resulting signal is expected to be identical to the desired track-gap signature. A preliminary background rate is obtained by performing an event selection. The resulting background rate after the selection process is 5e-5 Hz, which is a reasonable result given a neutrino flux of mHz. A more thorough selection taking into account the particle energies as well as IceCube's limited energy resolution is expected to lower the rate.

Aims. The aim of this work is to investigate any presence of transit timing variations (TTVs) in a sample of observed targets that has light curves in both K2 mission data and TESS mission data.  Methods. The original sample utilised here was one from the doctoral thesis of D. Soto (2020) with candidates from K2 data. Cross-referencing for corresponding light curves in TESS was done with a customised Python script created for the purposes of this work, automating the process of obtaining light curves using only one mission ID. A transit search was performed on the light curves of each mission separately with the Python software package OpenTS. The candidates with transits in both light curves were subjected to a TTV search using the Python software package PyTTV. The PyTTV software utilises both mission light curves in creating a joint light curve.  Results. Orbital periods, Porb, and transit center times, t0, for 30 targets were updated using joint light curves from the K2 and TESS missions. Seventeen of these systems are found to have non-linear trends in their transit times. These also have constraints for the periods and amplitudes of the TTVs.  The disposition distribution of the 30 systems is that 19 candidates are unregistered candidates, ten are registered planetary candidates or TOIs and eight are registered known planets.  Conclusions. Out of the reference sample by D. Soto (2020) consisting of 564 targets, 257 targets had a corresponding TESS light curve. Out of the 257 targets, a new sample of 45 targets was contrived through a transit search where they all show distinct transits in both missions light curves. Out of these, fifteen targets were not suitable for a TTV search. A final sample of 30 targets are presented, with seventeen targets showing signs of TTVs and thirteen targets showing a linear trend. The parameters of orbital period and transit centre times are updated for all 30 final candidates. Seventeen candidates are shown to have variations in the transit times and are presented with diagnostics. The candidates with transit timing variations should be further investigated for potential validation or follow-up observations. The unregistered candidates as well as the planetary candidates and TOIs should be considered for follow-up observations or similar validation, to confirm or discard a planetary status.

The determination of the solar oxygen abundance is a topic that has long beenunder debate, where the exact value has varied between researchers. These variationsin the oxygen abundance have implications on our understanding of the Sun and itsinterior as well as our understanding of other stars. The aim of this report is to explorethe di erences between three observations; the Liège, Hamburg and SST, and their effecton the solar oxygen abundance calculated from the 777 nm triplet. In the reportit was found that the abundance from the Liège and SST data was lower and in betteragreement (A(O) ≈ 8.709 dex) compared to the Hamburg data (A(O) ≈ 8.732 dex).One of the potential reasons for these di erences explored in the thesis were the e ectsof magnetic  elds. After comparing the di erences it was argued that the SST dataset as well as the Liège could be considered more reliable compared to the Hamburg.The argued abundance was therefore of a somewhat lower value which does not helplessen the inconsistency between solar models and helioseismology. / Bestämningen av mängden syre i solen har länge varit ett debatterat område där det exakta numeriska värdet varierat bland forskare. Dessa variationer av mängden syre ger konsekvenser för vår förståelse av solen och dess inre samt för vår förståelse av andra stjärnor. Syftet med denna rapport är att utforska skillnaderna mellan tre observationer; från Liège, Hamburg och SST, samt deras påverkan på mängden syre i solen beräknad från 777 nm tripletten. Rapporten fann att mängden syre beräknad från Liège- och SST-datan både var lägre samt stämde bättre överens (A(O) ≈ 8.709 dex) i jämförelse med mängden från Hamburg observationen (A(O) ≈ 8.732 dex). En potentiell anledning till skillnaden i resultat som utforskades i denna uppsats var påverkan av magnetiska fält. Efter jämförelse av skillnaderna kunde det konstateras att datan från SST så väl som från Liège kan anses mer pålitliga i förhållande till Hamburg-datan. Den förespråkade mängden syre var åt det lägre hållet vilket inte bidrar till minskningen av avvikelserna mellan modeller av solen och mätningar via helioseismologi.

Detecting neutrinos, especially ultra-high-energy (UHE) neutrinos, is inherently challenging. Highly sensitive detection devices are required to effectively capture these rare particles, which often results in significant noise in the data. This project focuses on enhancing the detection sensitivity of UHE neutrinos interacting with glacier ice by employing deep learning and transformer models. These models are trained on simulated data that mimics the radio signals produced by neutrino interactions in ice. The developed models have demonstrated improved performance compared to current hardware implementations, offering a promising advancement in neutrino detection technology.