The influence of the explosion anisotropies and of the circumstellar medium on the evolution of Supernova Remnants and on particle acceleration at their shocks
This thesis is dedicated to the analysis of X-ray observations of supernova remnants (SNRs), complemented with the synthesis of X-ray spectra employing 3-Dimensional Magneto-Hydrodynamic (MHD) models. The primary objective of this work is to acquire a deeper understanding of how the supernova (SN) explosion and the circumstellar medium (CSM) impact both on the evolution of SNRs and on the mechanisms governing particle acceleration.In particular, I address three key challenges: i) investigating the impact of the environment on electron acceleration through the analysis of the non-thermal radiation in the Kepler's SNR, ii) revealing explosion anisotropies and wind residuals in the Vela SNR through the analysis of X-ray observations, iii) predicting the X-ray emission of the fast expanding ejecta in SN 1987A through the synthesis of the XRISM-Resolve spectrum from a dedicated 3D MHD model.Synchrotron X-ray emission in young SNRs serves as a diagnostic tool to explore the population of high-energy electrons accelerated at the shock front and to understand the acceleration process. By conducting a spatially resolved spectral analysis using NuSTAR and XMM-Newton observations of Kepler's SNR, I study the non-thermal emission in hard X-rays, using a synchrotron radiation model in the loss-limited regime.The analysis reveals two distinct regimes of particle acceleration characterized by different Bohm factors.In the northern region, where the shock interacts with a dense CSM, I observe more efficient acceleration compared to the southern region, where the shock velocity is higher, and there are no indications of shock interaction with dense CSM. These results suggest an enhanced efficiency of the acceleration process in regions where the shock-CSM interaction generates an amplified and turbulent magnetic field.In the proposed scenario, the synchrotron cooling time scale aligns with the acceleration time scale. Conversely, the low speed of a shock propagating in a dense medium is expected to increase the acceleration time scale, resulting in a lower maximum electron energy (and fainter non-thermal X-ray flux) for a given SNR age. To deepen this scenario at smaller scales, I investigate the temporal evolution of the synchrotron flux, taking advantage of the two deepest Chandra/ACIS X-ray observations of Kepler's SNR, performed in 2006 and 2014. Analyzing the spectra of different filaments in the northern shell, I measure their proper motion and estimate the ratio between the acceleration time-scale and the synchrotron cooling time.I identify a region with very low shock velocity and find that the acceleration time-scale is longer than the synchrotron cooling time therein. In this region, I measure a significant decrease in flux from 2006 to 2014, thus obtaining the first evidence of fading synchrotron emission in Kepler's SNR. Overall, these results contribute to a coherent understanding of the diverse electron acceleration regimes observed in Kepler's SNR and associated with its expansion into a non-uniform CSM.Core-collapse SNRs have intricate morphologies arising from inherent asymmetries in the SN explosion and the propagation of explosion shock waves in highly heterogeneous environments.The Vela SNR, indeed, exhibits multiple ejecta fragments, commonly referred to as shrapnel, extending beyond the forward shock. Recent investigations have identified elevated silicon (Si) abundance in two specific shrapnel, denoted as A and G, positioned in opposite directions relative to the SNR center.This observation hints at the potential presence of a Si-rich jet-counterjet structure.To address this issue I conduct an analysis of an XMM-Newton observation focused on a luminous clump situated behind shrapnel G, which aligns with the trajectory connecting shrapnel A and G, with the aim to scrutinize its physical and chemical properties, determining its association with the supposed jet-like structure. I identify two distinct structures, each exhibiting different physical characteristics. The first structure displays a remarkable elongation along the axis connecting shrapnel A and G.Despite its X-ray spectrum being considerably softer than that of the other two shrapnel, hindering Si abundance determination, its physical and chemical properties are found to be consistent with those of shrapnel A and G.The second structure exhibits a higher temperature and resembles a thin filament. Thanks to the analysis of archived ROSAT data, I find that this filament is part of an extensive and cohesive structure identified in the western rim of the shell.This feature is interpreted as a signature of a prior interaction between the remnant and the stellar wind from its progenitor star.The peculiar Ne/O ratio identified in the wind residual raises the possibility of a Wolf-Rayet progenitor for the Vela SNR. As for the case of SN 1987A, my research consists in evaluating the efficacy of the newly launched XRISM-Resolve high-resolution spectrometer in discerning distinctive signatures associated with shocked ejecta in SN 1987A.This celestial object presents a unique opportunity to scrutinize the transformation of a SN into a nascent SNR.Historically, the dominant source of X-ray emission has been the shocked CSM, with no conclusive identification of shocked ejecta. However, recent investigations provide compelling indications that the future X-ray emissions from SN 1987A will increasingly originate from the ejecta.Leveraging a state-of-the-art, self-consistent MHD simulation that intricately depicts the evolutionary stages from SN 1987A to its remnant, I generated a synthetic XRISM-Resolve spectrum for SN 1987A performance verification phase observation anticipated in 2024.My predictions distinctly highlight the prominent role of shocked ejecta in shaping the emission line profiles.Doppler broadening, resulting from the bulk motion along the line of sight of the rapidly expanding ejecta, is demonstrated to significantly increase the line widths beyond previously observed values. The quantitative comparison between my synthetic spectra and the actual XRISM spectra will provide a robust diagnostic for establishing a direct correlation between the broadened line emission and the newly shocked ejecta. This correlation, in turn, will facilitate the retrieval of essential information regarding the dynamics and chemical composition of the ejecta from the X-ray emission
