Context. The morphology and the distribution of material observed in supernova remnants (SNRs) reflect the interaction of the supernova (SN) blast wave with the ambient environment, the physical processes associated with the SN explosion, and the internal structure of the progenitor star. IC 443 is a mixed-morphology (MM) SNR located in a quite complex environment: it interacts with a molecular cloud in the northwestern and southeastern areas and with an atomic cloud in the northeast. Aims. In this work, we aim to investigate the origin of the complex morphology and multi-thermal X-ray emission observed in SNR IC 443 through the study of the effect of the inhomogeneous ambient medium in shaping its observed structure and an exploration of the main parameters characterizing the remnant. Methods. We developed a 3D hydrodynamic (HD) model for IC 443, which describes the interaction of the SNR with the environment, parametrized in agreement with the results of the multi-wavelength data analysis. We performed an ample exploration of the parameter space describing the initial blast wave and the environment, including the mass of the ejecta, the energy and position of the explosion, as well as the density, structure, and geometry of the surrounding clouds. From the simulations, we synthesized the X-ray emission maps and spectra and compared them with actual X-ray data collected by XMM-Newton. Results. Our model explains the origin of the complex X-ray morphology of SNR IC 443 in a natural way, with the ability to reproduce, for the first time, most of the observed features, including the centrally-peaked X-ray morphology (characteristic of MM SNRs) when considering the origin of the explosion at the position where the pulsar wind nebula CXOU J061705.3+222127 was at the time of the explosion. In the model that best reproduces the observations, the mass of the ejecta and the energy of the explosion are ~7 M⊙ and ~1 × 1051 erg, respectively. From the exploration of the parameter space, we find that the density of the clouds is n > 300 cm−3 and that the age of SNR IC 443 is ~8000 yr. Conclusions. The observed inhomogeneous ambient medium is the main property responsible for the complex structure and the X-ray morphology of SNR IC 443, resulting in a very asymmetric distribution of the ejecta due to the off-centered location of the explosion inside the cavity formed by the clouds. It can be argued that the centrally peaked morphology (typical of MM SNRs) is a natural consequence of the interaction with the complex environment. A combination of high resolution X-ray observations and accurate 3D HD modeling is needed to confirm whether this scenario is applicable to other MM SNRs.

Context. X-ray observations of protostellar jets show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary. They are interpreted as shock diamonds. Aims. We aim at investigating the physics that guides the formation of X-ray emitting stationary shocks in protostellar jets, the role of the magnetic field in determining the location, stability, and detectability in X-rays of these shocks, and the physical properties of the shocked plasma. Methods. We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations modelling supersonic jets ramming into a magnetized medium and explored different configurations of the magnetic field. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. We compared the model results with observations, via the emission measure and the X-ray luminosity synthesized from the simulations. Results. Our model explains the formation of X-ray emitting stationary shocks in a natural way. The magnetic field collimates the plasma at the base of the jet and forms there a magnetic nozzle. After an initial transient, the nozzle leads to the formation of a shock diamond at its exit which is stationary over the time covered by the simulations (∼ 40 − 60 yr; comparable with time scales of the observations). The shock generates a point-like X-ray source located close to the base of the jet with luminosity comparable with that inferred from X-ray observations of protostellar jets. For the range of parameters explored, the evolution of the post-shock plasma is dominated by the radiative cooling, whereas the thermal conduction slightly affects the structure of the shock.

Context. The manifold phases in the evolution of a core-collapse (CC) supernova (SN) play an important role in determining the physical properties and morphology of the resulting supernova remnant (SNR). Thus, the complex morphology of SNRs is expected to reflect possible asymmetries and structures developed during and soon after the SN explosion. Aims. The aim of this work is to bridge the gap between CC SNe and their remnants by investigating how post-explosion anisotropies in the ejecta influence the structure and chemical properties of the remnant at later times. Methods. We performed three-dimensional magneto-hydrodynamical simulations starting soon after the SN event and following the evolution of the system in the circumstellar medium, which includes the wind of the stellar progenitor, for 5000 yr, obtaining the physical scenario of a SNR. Here we focused the analysis on the case of a progenitor red supergiant of 19.8 M⊙. We also investigated how a post-explosion large-scale anisotropy in the SN affects the ejecta distribution and the matter mixing of heavy elements in the remnant during the first 5000 yr of evolution. Results. In the case of a spherically symmetric SN explosion without large-scale anisotropies, the remnant roughly keeps memory of the original onion-like layering of ejecta soon after the SN event. Nevertheless, as the reverse shock hits the ejecta, the element distribution departs from a homologous expansion because of the slowing down of the outermost ejecta layers due to interaction with the reverse shock. In the case of a large-scale anisotropy developed after the SN, we found that the chemical stratification in the ejecta can be strongly modified and the original onion-like layering is not preserved. The anisotropy may cause spatial inversion of ejecta layers, for instance leading to Fe/Si-rich ejecta outside the O shell, and may determine the formation of Fe/Si-rich jet-like features that may protrude the remnant outline. The level of matter mixing and the properties of the jet-like feature are sensitive to the initial physical (density and velocity) and geometrical (size and position) initial characteristics of the anisotropy.

Vera C. Rubin Observatory, through the Legacy Survey of Space and Time (LSST), will allow us to derive a panchromatic view of variability in young stellar objects (YSOs) across all relevant timescales. Indeed, both short-term variability (on timescales of hours to days) and long-term variability (months to years), predominantly driven by the dynamics of accretion processes in disk-hosting YSOs, can be explored by taking advantage of the multiband filters option available in Rubin LSST, in particular the u, g, r, i filters that enable us to discriminate between photospheric stellar properties and accretion signatures. The homogeneity and depth of sky coverage that will be achieved with LSST will provide us with a unique opportunity to characterize the time evolution of disk accretion as a function of age and varying environmental conditions (e.g., field crowdedness, massive neighbors, metallicity) by targeting different star-forming regions. In this contribution to the Rubin LSST Survey Strategy Optimization Focus Issue, we discuss how implementing a dense observing cadence to explore short-term variability in YSOs represents a key complementary effort to the Wide–Fast–Deep observing mode that will be used to survey the sky over the full duration of the main survey (≈10 yr). The combination of these two modes will be vital to investigate the connection between the inner-disk dynamics and longer-term eruptive variability behaviors, such as those observed on EX Lupi–type objects.

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