Early X-ray emission from Type Ia supernovae originating from symbiotic progenitors or recurrent novae

One of the key observables for determining the progenitor nature of Type Ia supernovae is provided by their immediate circumstellar medium, which according to several models should be shaped by the progenitor binary system. So far, X-ray and radio observations indicate that the surroundings are very tenuous, producing severe upper-limits on the mass loss from winds of the progenitors. In this study, we perform numerical hydro-dynamical simulations of the interaction of the SN ejecta with circumstellar structures formed by possible mass outflows from the progenitor systems and we estimate numerically the expected numerical X-ray luminosity. We consider two kinds of circumstellar structures: a) A circumstellar medium formed by the donor star's stellar wind, in case of a symbiotic binary progenitor system; b) A circumstellar medium shaped by the interaction of the slow wind of the donor star with consecutive nova outbursts for the case of a symbiotic recurrent nova progenitor system. For the hydro-simulations we used well-known Type Ia supernova explosion models, as well as an approximation based on a power law model for the density structure of the outer ejecta. We confirm the strict upper limits on stellar wind mass loss, provided by simplified interpretations of X-ray upper limits of Type Ia supernovae. However, we show that supernova explosions going off in the cavities created by repeated nova explosions, provide a possible explanation for the lack of X-ray emission from supernovae originating from symbiotic binaries. Moreover, the velocity structure of circumstellar medium, shaped by a series of nova explosion matches well with the Na absorption features seen in absorption toward several Type Ia supernovae.Comment: 11 pages, 12 figures, submitted to MNRA

The many sides of RCW 86: a type Ia supernova remnant evolving in its progenitor's wind bubble

We present the results of a detailed investigation of the Galactic supernova remnant RCW 86 using the XMM-Newton X-ray telescope. RCW 86 is the probable remnant of SN 185 A.D, a supernova that likely exploded inside a wind-blown cavity. We use the XMM-Newton Reflection Grating Spectrometer (RGS) to derive precise temperatures and ionization ages of the plasma, which are an indication of the interaction history of the remnant with the presumed cavity. We find that the spectra are well fitted by two non-equilibrium ionization models, which enables us to constrain the properties of the ejecta and interstellar matter plasma. Furthermore, we performed a principal component analysis on EPIC MOS and pn data to find regions with particular spectral properties. We present evidence that the shocked ejecta, emitting Fe-K and Si line emission, are confined to a shell of approximately 2 pc width with an oblate spheroidal morphology. Using detailed hydrodynamical simulations, we show that general dynamical and emission properties at different portions of the remnant can be well-reproduced by a type Ia supernova that exploded in a non-spherically symmetric wind-blown cavity. We also show that this cavity can be created using general wind properties for a single degenerate system. Our data and simulations provide further evidence that RCW 86 is indeed the remnant of SN 185, and is the likely result of a type Ia explosion of single degenerate origin.Comment: Accepted for publication in MNRAS. 16 pages, 13 figure

Modeling the interaction of thermonuclear supernova remnants with circumstellar structures: The case of Tycho's supernova remnant

The well-established Type Ia remnant of Tycho's supernova (SN 1572) reveals discrepant ambient medium density estimates based on either the measured dynamics or on the X-ray emission properties. This discrepancy can potentially be solved by assuming that the supernova remnant (SNR) shock initially moved through a stellar wind bubble, but is currently evolving in the uniform interstellar medium with a relatively low density. We investigate this scenario by combining hydrodynamical simulations of the wind-loss phase and the supernova remnant evolution with a coupled X-ray emission model, which includes non-equilibrium ionization. For the explosion models we use the well-known W7 deflagration model and the delayed detonation model that was previously shown to provide good fits to the X-ray emission of Tycho's SNR. Our simulations confirm that a uniform ambient density cannot simultaneously reproduce the dynamical and X-ray emission properties of Tycho. In contrast, models that considered that the remnant was evolving in a dense, but small, wind bubble reproduce reasonably well both the measured X-ray emission spectrum and the expansion parameter of Tycho's SNR. Finally, we discuss possible mass loss scenarios in the context of single- and double-degenerate models which possible could form such a small dense wind bubble.Comment: 12 pages, 7 figures, accepted for publication in MNRA

Progenitor's signatures in Type Ia supernova remnants

The remnants of Type Ia supernovae can provide important clues about their progenitor-histories. We discuss two well-observed supernova remnants (SNRs) that are believed to result from a Type Ia SN and use various tools to shed light on the possible progenitor history. We find that Kepler's SNR is consistent with a symbiotic binary progenitor consisted of a white dwarf and an AGB star. Our hydrosimulations can reproduce the observed kinematic and morphological properties. For Tycho's remnant we use the characteristics of the X-ray spectrum and the kinematics to show that the ejecta has likely interacted with dense circumstellar gas.Comment: 4 pages, 9 figures, proceedings for IAU Symposium 281, Padova, July 201

Rebellion in Southern Rhodesia 1896-1897

Η παρούσα μελέτη εξετάζει τις εξεγέρσεις των Ndebele και Shona εναντίον της Βρετανικής Εταιρείας Νοτίου Αφρικής κατά τα έτη 1896-1897. Στόχος της έρευνας είναι να αναδειχθούν η φύση, τα αίτια, η εξέλιξη και τα αποτελέσματα της αντιαποικιακής εξέγερσης των δύο φυλών, της πρώτης σοβαρής αντιαποικιακής απόπειρας στον χώρο της Υποσαχάριας Αφρικής. Οι εξεγέρσεις αυτές συνιστούν προνομιακό πεδίο έρευνας διότι επιτρέπουν την ενδελεχή μελέτη των τοπικών κοινωνιών και ταυτόχρονα υποδεικνύουν το ποιόν της βρετανικής αποικιακής παρουσίας στην περιοχή της επονομαζόμενης Νότιας Ροδεσίας. Ιδιαίτερη έμφαση δίνεται στα νέα δεδομένα που επέβαλλε η αποικιακή κυριαρχία στην περιοχή, τα οποία οδήγησαν στην εξέγερση του ιθαγενούς πληθυσμού. Τέλος παρουσιάζεται ο αποικιακός νομιμοποιητικός λόγος ως απόπειρα δικαιολόγησης των βρετανικών πολεμικών πρακτικών αλλά και της αποικιακής παρουσίας των Βρετανών στη Νότια Ροδεσία εν γένει.The present study examines the rebellion of Ndebele and Shona against the rule of the British South Africa Company in 1896-97. The purpose of this study is to point out the nature, the causes, the development, and the results of the natives’ anti-colonial struggle. This was the first serious attempt to overthrow the British colonial rule in Sub-Saharan Africa. The study of this rebellion sheds light not only on the characteristics of the local societies but also on the nature of the British colonial engagement in Southern Rhodesia. A major concern of this study is to give prominence to the new situation caused by the British conquest and the grievances of Shona and Ndebele, which led to the rebellion. Last but not least, special focus will be given to the legitimizing colonial discourse, as an attempt to justify not only the British war conduct but also the British colonial expansion in Southern Rhodesia in general

The Interaction of Type Ia Supernovae with Planetary Nebulae: the Case of Kepler's Supernova Remnant

One of the key methods for determining the unknown nature of Type Ia supernovae (SNe Ia) is the search for traces of interaction between the SN ejecta and the circumstellar structures at the resulting supernova remnants (SNRs Ia). So far, the observables that we receive from well-studied SNRs Ia cannot be explained self-consistently by any model presented in the literature. In this study, we suggest that the circumstellar medium (CSM) being observed to surround several SNRs Ia was mainly shaped by planetary nebulae (PNe) that originated from one or both progenitor stars. Performing two-dimensional hydrodynamic simulations, we show that the ambient medium shaped by PNe can account for several properties of the CSM that have been found to surround SNe Ia and their remnants. Finally, we model Kepler's SNR considering that the SN explosion occurred inside a bipolar PN. Our simulations show good agreement with the observed morphological and kinematic properties of Kepler's SNR. In particular, our model reproduces the current expansion parameter of Kepler's SNR, the partial interaction of the remnant with a dense CSM at its northern region and finally the existence of two opposite protrusions (`ears') at the equatorial plane of the SNR.Comment: Accepted for publication in Galaxies, 7 page

The imprint of a symbiotic binary progenitor on the properties of Kepler's supernova remnant

We present a model for the Type Ia supernova remnant (SNR) of SN 1604, also known as Kepler's SNR. We find that its main features can be explained by a progenitor model of a symbiotic binary consisting of a white dwarf and an AGB donor star with an initial mass of 4-5 M_sun. The slow, nitrogen rich wind emanating from the donor star has partially been accreted by the white dwarf, but has also created a circumstellar bubble. Based on observational evidence, we assume that the system moves with a velocity of 250 km/s. Due to the systemic motion the interaction between the wind and the interstellar medium has resulted in the formation of a bow shock, which can explain the presence of a one-sided, nitrogen rich shell. We present two-dimensional hydrodynamical simulations of both the shell formation and the SNR evolution. The SNR simulations show good agreement with the observed kinematic and morphological properties of Kepler's SNR. Specifically, the model reproduces the observed expansion parameters (m=V/(R/t)) of m=0.35 in the north and m=0.6 in the south of Kepler's SNR. We discuss the variations among our hydrodynamical simulations in light of the observations, and show that part of the blast wave may have traversed through the one-sided shell completely. The simulations suggest a distance to Kepler's SNR of 6 kpc, or otherwise require that SN 1604 was a sub-energetic Type Ia explosion. Finally, we discuss the possible implications of our model for Type Ia supernovae and their remnants in general.Comment: 13 pages, 9 figures. Submitted to A&

Unconventional Control of Electromagnetic Waves with Applications in Electrically Small Antennas, Nondiffracting Waves, and Metasurfaces

Although electromagnetics is a well-established field within physics and engineering, it is also a rather dynamic one. Our ever increasing need for connectivity and the rise of medical and military applications constantly create new challenges for researchers in electromagnetics. In this thesis, unconventional methods are proposed for tackling some of these challenges by manipulating the electromagnetic fields in different regions: reactive near field, radiative near field, and far field. The first topic examined pertains to the development of antennas for Internet of Things (IoT) nodes with extremely small form factors and low power consumption. As a result, they require small and relatively efficient antennas that can be tightly integrated within the node. The antennas should be able to operate with lossy and metallic components in their near field, while maintaining adequate performance. A type of antenna, called a 3D loop, is designed to fulfill these specifications, and is used in two compact IoT systems. The second thrust aims at developing devices that generate Bessel beams and X waves in their radiative near field. Bessel beams are a class of exotic beams with nondiffracting and self-healing properties. Here, two radiator designs are presented, capable of generating Bessel beams with minimal deviation of their parameters over a broad bandwidth. This allows the generation of nondiffracting and nondispersive pulses (X waves) that remain highly localized within the device’s radiative near field. The final topic examined aims at analytically modeling the electromagnetic properties of patterned metallic sheets. Such sheets are the building blocks of metasurfaces, which are two dimensional devices that manipulate the properties of a propagating wavefront (amplitude, phase, polarization). Having analytical models for sheets that realize arbitrary electromagnetic properties significantly expedites their design, as opposed to relying on databases of simulated geometries.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/150024/1/nchiot_1.pd