We present an analysis of archival Chandra observations of the mixed-morphology remnant 3C400.2. We analysed spectra of different parts of the remnant to observe if the plasma properties provide hints on the origin of the mixed-morphology class. Thes
e remnants often show overionization, which is a sign of rapid cooling of the thermal plasma, and super-solar abundances of elements which is a sign of ejecta emission. Our analysis shows that the thermal emission of 3C400.2 can be well explained by a two component non-equilibrium ionization model, of which one component is underionized, has a high temperature ($kT approx 3.9$ keV) and super-solar abundances, while the other component has a much lower temperature ($kT approx 0.14$ keV), solar abundances and shows signs of overionization. The temperature structure, abundance values and density contrast between the different model components suggest that the hot component comes from ejecta plasma, while the cooler component has an interstellar matter origin. This seems to be the first instance of an overionized plasma found in the outer regions of a supernova remnant, whereas the ejecta component of the inner region is underionized. In addition, the non-ionization equilibrium plasma component associated with the ejecta is confined to the central, brighter parts of the remnant, whereas the cooler component is present mostly in the outer regions. Therefore our data can most naturally be explained by an evolutionary scenario in which the outer parts of the remnant are cooling rapidly due to having swept up high density ISM, while the inner parts are very hot and cooling inefficiently due to low density of the plasma. This is also known as the relic X-ray scenario.
Astrophysical shocks are often collisionless shocks. An open question about collisionless shocks is whether electrons and ions each establish their own post-shock temperature, or whether they quickly equilibrate in the shock region. Here we provide s
imple relations for the minimal amount of equilibration to expect. The basic assumption is that the enthalpy-flux of the electrons is conserved separately, but that all particle species should undergo the same density jump across the the shock. This assumption results in an analytic treatment of electron-ion equilibration that agrees with observations of collisionless shocks: at low Mach numbers ($<2$) the electrons and ions are close to equilibration, whereas for Mach numbers above $M sim 60$ the electron-ion temperature ratio scales with the particle masses $T_e/T_i = m_e/m_i$. In between these two extremes the electron-ion temperature ratio scales as $T_e/T_i propto 1/M_s^2$. This relation also hold if adiabatic compression of the electrons is taken into account. For magnetised plasmas the compression is governed by the magnetosonic Mach number, whereas the electron-ion temperatures are governed by the sonic Mach number. The derived equations are in agreement with observational data at low Mach numbers, but for supernova remnants the relation requires that the inferred Mach numbers for the observations are over- estimated, perhaps as a result of upstream heating in the cosmic-ray precursor. In addition to predicting a minimal electron/ion temperature ratio, we also heuristically incorporate ion-electron heat exchange at the shock, quantified with a dimensionless parameter ${xi}$. Comparing the model to existing observations in the solar system and supernova remnants suggests that the data are best described by ${xi} sim 5$ percent. (Abridged abstract.)
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 XM
M-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.
It is shown that, under some generic assumptions, shocks cannot accelerate particles unless the overall shock Mach number exceeds a critical value M > sqrt(5). The reason is that for M <= sqrt(5) the work done to compress the flow in a particle precu
rsor requires more enthalpy flux than the system can sustain. This lower limit applies to situations without significant magnetic field pressure. In case that the magnetic field pressure dominates the pressure in the unshocked medium, i.e. for low plasma beta, the resistivity of the magnetic field makes it even more difficult to fulfil the energetic requirements for the formation of shock with an accelerated particle precursor and associated compression of the upstream plasma. We illustrate the effects of magnetic fields for the extreme situation of a purely perpendicular magnetic field configuration with plasma beta = 0, which gives a minimum Mach number of M = 5/2. The situation becomes more complex, if we incorporate the effects of pre-existing cosmic rays, indicating that the additional degree of freedom allows for less strict Mach number limits on acceleration. We discuss the implications of this result for low Mach number shock acceleration as found in solar system shocks, and shocks in clusters of galaxies.
Aims: We want to probe the physics of fast collision-less shocks in supernova remnants. In particular, we are interested in the non-equilibration of temperatures and particle acceleration. Specifically, we aim to measure the oxygen temperature with r
egards to the electron temperature. In addition, we search for synchrotron emission in the northwestern thermal rim. Methods: This study is part of a dedicated deep observational project of SN 1006 using XMM-Newton, which provides us with currently the best resolution spectra of the bright northwestern oxygen knot. We aim to use the reflection grating spectrometer to measure the thermal broadening of the O vii line triplet by convolving the emission profile of the remnant with the response matrix. Results: The line broadening was measured to be {sigma}_e = 2.4 pm 0.3 eV, corresponding to an oxygen temperature of 275$^{+72}_{-63}$ keV. From the EPIC spectra we obtain an electron temperature of 1.35 pm 0.10 keV. The difference in temperature between the species provides further evidence of non-equilibration of temperatures in a shock. In addition, we find evidence for a bow shock that emits X-ray synchrotron radiation, which is at odds with the general idea that due to the magnetic field orientation only in the NE and SW region X-ray synchrotron radiation should be emitted. We find an unusual H{alpha} and X-ray synchrotron geometry, in that the H{alpha} emission peaks downstream of the synchrotron emission. This may be an indication for a peculiar H{alpha} shock, in which the density is lower and neutral fraction are higher than in other supernova remnants, resulting in a peak in H{alpha} emission further downstream of the shock.
The origin of cosmic rays holds still many mysteries hundred years after they were first discovered. Supernova remnants have for long been the most likely sources of Galactic cosmic rays. I discuss here some recent evidence that suggests that superno
va remnants can indeed efficiently accelerate cosmic rays. For this conference devoted to the Astronomical Institute Utrecht I put the emphasis on work that was done in my group, but placed in a broader context: efficient cosmic-ray acceleration and the im- plications for cosmic-ray escape, synchrotron radiation and the evidence for magnetic- field amplification, potential X-ray synchrotron emission from cosmic-ray precursors, and I conclude with the implications of cosmic-ray escape for a Type Ia remnant like Tycho and a core-collapse remnant like Cas A.
RX J0720.4-3125 is the most peculiar object among a group of seven isolated X-ray pulsars (the so-called Magnificent Seven), since it shows long-term variations of its spectral and temporal properties on time scales of years. This behaviour was expla
ined by different authors either by free precession (with a seven or fourteen years period) or possibly a glitch that occurred around $mathrm{MJD=52866pm73 days}$. We analysed our most recent XMM-Newton and Chandra observations in order to further monitor the behaviour of this neutron star. With the new data sets, the timing behaviour of RX J0720.4-3125 suggests a single (sudden) event (e.g. a glitch) rather than a cyclic pattern as expected by free precession. The spectral parameters changed significantly around the proposed glitch time, but more gradual variations occurred already before the (putative) event. Since $mathrm{MJDapprox53000 days}$ the spectra indicate a very slow cooling by $sim$2 eV over 7 years.
Supernova remnants are beautiful astronomical objects that are also of high scientific interest, because they provide insights into supernova explosion mechanisms, and because they are the likely sources of Galactic cosmic rays. X-ray observations ar
e an important means to study these objects.And in particular the advances made in X-ray imaging spectroscopy over the last two decades has greatly increased our knowledge about supernova remnants. It has made it possible to map the products of fresh nucleosynthesis, and resulted in the identification of regions near shock fronts that emit X-ray synchrotron radiation. In this text all the relevant aspects of X-ray emission from supernova remnants are reviewed and put into the context of supernova explosion properties and the physics and evolution of supernova remnants. The first half of this review has a more tutorial style and discusses the basics of supernova remnant physics and thermal and non-thermal X-ray emission. The second half offers a review of the recent advances.The topics addressed there are core collapse and thermonuclear supernova remnants, SN 1987A, mature supernova remnants, mixed-morphology remnants, including a discussion of the recent finding of overionization in some of them, and finally X-ray synchrotron radiation and its consequences for particle acceleration and magnetic fields.
We co-added the available XMM-Newton RGS spectra for each of the isolated X-ray pulsars RX,J0720.4$-$3125, RX,J1308.6+2127 (RBS,1223), RX,J1605.3+3249 and RX,J1856.4$-$3754 (four members of the Magnificent Seven) and the Three Musketeers Geminga, PSR
,B0656+14 and PSR,B1055-52. We confirm the detection of a narrow absorption feature at 0.57 keV in the co-added RGS spectra of RX,J0720.4$-$3125 and RX,J1605.3+3249 (including most recent observations). In addition we found similar absorption features in the spectra of RX,J1308.6+2127 (at 0.53 keV) and maybe PSR,B1055-52 (at 0.56 keV). The absorption feature in the spectra of RX,J1308.6+2127 is broader than the feature e.g. in RX,J0720.4$-$3125. The narrow absorption features are detected with 2$sigma$ to 5.6$sigma$ significance. Although very bright and frequently observed, there are no absorption features visible in the spectra of RX,J1856.4$-$3754 and PSR,B0656+14, while the co-added XMM-Newton RGS spectrum of Geminga has not enough counts to detect such a feature. We discuss a possible origin of these absorption features as lines caused by the presence of highly ionised oxygen (in particular OVII and/or OVI at 0.57 keV) in the interstellar medium and absorption in the neutron star atmosphere, namely the absorption features at 0.57 keV as gravitational redshifted ($g_{r}$=1.17) OVIII.
We present a statistical analysis of the X-ray luminosity of rotation powered pulsars and their surrounding nebulae using the sample of Kargaltsev & Pavlov (2008) and we complement this with an analysis of the gamma-ray-emission of Fermi detected pul
sars. We report a strong trend in the efficiency with which spin-down power is converted to X-ray and gamma-ray emission with characteristic age: young pulsars and their surrounding nebulae are efficient X-ray emitters, whereas in contrast old pulsars are efficient gamma-ray emitters. We divided the X-ray sample in a young (Tau < 1.7x10^4 yr) and old sample and used linear regression to search for correlations between the logarithm of the X-ray and gamma-ray luminosities and the logarithms of the periods and period derivatives. The X-ray emission from young pulsars and their nebulae are both consistent with L_X ~ Pdot^3/P^6. For old pulsars and their nebulae the X-ray luminosity is consistent with a more or less constant efficiency eta = L_X/Edot = ~ 8x10^-5. For the gamma-ray luminosity we confirm that L_gamma ~ Edot^(1/2). We discuss these findings in the context of pair production inside pulsar magnetospheres and the striped wind model. We suggest that the striped wind model may explain the similarity between the X-ray properties of the pulsar wind nebulae and the pulsars themselves, which according to the striped wind model may both find their origin outside the light cylinder, in the pulsar wind zone.
