Oxygen line mapping of SN 1006 with Suzaku

SN 1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region to region in the SNR; the north region is bright in nonthermal, while dim in thermal; the east region is bright in both nonthermal and thermal; the inner region shows dim nonthermal and bright thermal emission. The photon index is the smallest in the north region.     

A physical interpretation of the jet-like X-ray emission from supernova remnant W49B

In the framework of the study of supernova remnants and their complex interaction with the interstellar medium and the circumstellar material, we focus on the galactic supernova remnant W49B. Its morphology exhibits an X-ray bright elongated nebula, terminated on its eastern end by a sharp perpendicular structure aligned with the radio shell. The X-ray spectrum of W49B is characterized by strong K emission lines from Si, S, Ar, Ca, and Fe. There is a variation of the temperature in the remnant with the highest temperature found in the eastern side and the lowest one in the western side. The analysis of the recent observations of W49B indicates that the remnant may be the result of an asymmetric bipolar explosion where the ejecta are collimated along a jet-like structure and the eastern jet is hotter and more Fe-rich than the western one. Another possible scenario associates the X-ray emission with a spherical explosion where parts of the ejecta are interacting with a dense belt of ambient material. To overcome this ambiguity we present new results of the analysis of an XMM-Newton observation and we perform estimates of the mass and energy of the remnant. We conclude that the scenario of an anisotropic jet-like explosion explains quite naturally our observation results, but the association of W49B with a hypernova and a γ-ray burst, although still possible, is not directly supported by any evidence.     

The structure of the IC443 supernova remnant complex derived from ROSAT and Ginga observations

Radio observations have shown that the emission from IC443 can be attributed to three, partially incomplete shells. The two smaller diameter shells are bright in X-rays, whereas the X-ray extent of the largest one has been discovered only recently in the ROSAT All-Sky-Survey. This new X-ray shell — G189.6+3.3 — is well explained by a separate old ( 10⁵yr) supernova remnant (SNR), in contrast to the IC443 proper SNR, the age of which has been estimated to 10³yr. Spatial structure of the X-ray absorption observed with ROSAT suggests that G189.6+3.3 is located in front of a molecular cloud while the two smaller subshells previously known as IC443 are behind it. This geometry is confirmed by the observation of an additional absorption ridge across IC443, which is produced by a shell of cool and dense matter associated with G189.6+3.3.     

X-ray emission from supernova remnants observed with ROSAT

Spectrally resolved X-ray images of galactic supernova remnants have been obtained both from the ROSAT all-sky survey and a number of pointed observations. There is substantial evidence for significant spatial variation in temperature, density and pressure across the older, thermal remnants like the Vela SNR, the Cygnus Loop and the North Polar Spur. Both the brightness distribution and the pressure variations observed point towards recently shocked interstellar clouds and filaments, which dominate the X-ray emission pattern. Across the Puppis-A SNR an arc-shaped absorption structure has been detected, which is demonstrated to be produced by cold gas located close to the shock front of the Vela SNR. Across IC443 a similar absorption pattern has been observed, which is created by a cold shell associated with a previously unknown, ROSAT discovered SNR, which lies in front of IC443. Finally, a statistically overview of the SNRs detected in the ROSAT all-sky survey is presented. About half of the catalogued radio remnants have been observed in the survey and another 90 sources have been found which are considered to be candidates of new SNRs.     

XMM-Newton observations across the Cygnus Loop from northeastern rim to southwestern rim

We have observed the Cygnus Loop from the northeast (NE) to the southwest (SW) with XMM-Newton. We extracted spectra from 3′-spaced annular regions across the Loop and fitted them either with a one-kT_e-component non-equilibrium ionization (NEI) model or with two-kT_e-component NEI model. We found that the two-kT_e-component model yields significantly better fits in almost all the spectra than the one-kT_e-component model. Judging from the abundances, the high-kT_e-component in the two-temperature model must be fossil ejecta while the low-kT_e-component comes from the swept-up interstellar medium (ISM). The distributions of Ne, Mg, Si, and S for fossil ejecta appear to retain the onion-skin structure at the time of a supernova explosion, suggesting that significant overturning of the ejecta has not occurred yet. Comparing the relative abundances of fossil ejecta estimated for the entire Cygnus Loop with those from theoretical calculations for Type-II SN, the mass of the progenitor star is likely to be ∼13 M_⊙. The trends of the radial profiles of kT_e and emission integral for the swept-up ISM are adequately described by the Sedov model, suggesting that the swept-up ISM is concentrated in a shell-like structure. Comparing our data with the Sedov model, we found the ambient medium density to be ∼0.7 cm⁻³. Then, we estimated the total mass of the swept-up ISM and the age of the remnant to be ∼130 M_⊙ and 13,000 years, respectively. Note that if the explosion occurred within a stellar wind cavity, then the density in the cavity, the total swept-up mass in the cavity, and the age of the remnant are estimated to be ∼0.14 cm⁻³, ∼25 M_⊙, and ∼10,000 years, respectively.     

XMM-Newton survey of non-thermal shell candidates: Preliminary results on DA 530

The investigation of the general properties of non-thermal (NT) X-ray shell supernova remnants (SNRs), of which SN 1006 is the prototype, is important to understand how electrons are accelerated in SNR shocks and what is the origin of cosmic rays. Using the XMM-Newton satellite, we are carrying on a survey of putative non-thermal SNR candidates previously unknown or little studied in the X-ray band, in order to investigate the different manifestations of NT emission in SNR shells. The SNRs we have selected are likely to expand in a low density medium, and therefore to have a low thermal X-ray emission, that usually outshines the non-thermal one. We report here preliminary results obtained on the SNR shell DA 530.     

Cosmic ray acceleration by supernova shocks

We analyse the results of recent measurements of nonthermal emission from individual supernova remnants (SNRs) and their correspondence to the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is shown that the theory fits these data in a satisfactory way and provides the strong evidences for the efficient CR production in SNRs accompanied by significant magnetic field amplification. Magnetic field amplification leads to considerable increase of CR maximum energy so that the spectrum of CRs accelerated in SNRs is consistent with the requirements for the formation of Galactic CR spectrum up to the energy ∼10¹⁷ eV.     

X-ray plasma ejections and jets from solar compact flares observed with the Yohkoh soft X-ray telescope

Yohkoh soft X-ray observations have revealed coronal X-ray plasma ejections and jets associated with solar flares. We have studied an X-ray plasma ejection on 1993 November 11 in detail, as a typical example of X-ray plasma ejections (possibly plasmoids expected from the reconnection model). The results are as follows: (1) The shape of the ejected material is a loop before it begins to rise. (2) The ejecta are already heated to 5 – 16 MK before rising. (3) The kinetic energy of the ejecta is smaller than the thermal energy content of the ejecta. (4) The thermal energy of the ejecta is smaller than that of the flare regions. (5) The acceleration occurs during the impulsive phase. These results are compared with the characteristics of X-ray jets, and a possible interpretation (for both plasmoids and jets) based on the magnetic reconnection model is briefly discussed.     

New evidence for strong non-thermal effects in Tycho’s supernova remnant

For the case of Tycho’s supernova remnant (SNR), we present the relation between the blast wave and contact discontinuity radii calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is very close to the shock radius. Therefore a consistent explanation of these observations can be given in terms of efficient CR acceleration which makes the medium more compressible.     

A model grid for the spectral analysis of X-ray emission in young Type Ia supernova remnants

We address a new set of models for the spectral analysis of the X-ray emission from young, ejecta-dominated Type Ia supernova remnants. These models are based on hydrodynamic simulations of the interaction between Type Ia supernova explosion models and the surrounding ambient medium, coupled to self-consistent ionization and electron heating calculations in the shocked supernova ejecta, and the generation of synthetic spectra with an appropriate spectral code. The details are provided elsewhere, but in this paper we concentrate on a specific class of Type Ia explosion models (delayed detonations), commenting on the differences that arise between their synthetic X-ray spectra under a variety of conditions.     

Remnants of compact binary mergers

We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae, which will affect the dynamical evolution of their remnants. The ejecta of mergers consist of very neutron rich nuclei. Some of these neutron rich nuclei will produce observational signatures in form of gamma ray lines during their decay. The composition of the ejecta might even give interesting constraints about the internal structure of the neutron star. We further discuss the possibility that merger remnants appear as recently discovered ‘dark accelerators’ which are extended TeV sources which lack emission in other bands.     

Supernova remnants

Optical observations of young supernova remnants can give information on the abundance structure of the supernova ejecta, from which properties of the supernova explosion can be deduced. Young remnants also act as laboratories for fast shock wave phenomena. Observations of X-ray and optical line emission show that while a collisionless shock wave does form, it is far from thermal equilibrium. Some young remnants are promising candidates for particle acceleration in shock waves, while in other remnants a central compact object is probably responsible for particle acceleration.     

Evolution of magnetic fields and cosmic ray acceleration in supernova remnants

Observations show that the magnetic field in young supernova remnants (SNRs) is significantly stronger than can be expected from the compression of the circumstellar medium (CSM) by a factor of four expected for strong blast waves. Additionally, the polarization is mainly radial, which is also contrary to expectation from compression of the CSM magnetic field. Cosmic rays (CRs) may help to explain these two observed features. They can increase the compression ratio to factors well over those of regular strong shocks by adding a relativistic plasma component to the pressure, and by draining the shock of energy when CRs escape from the region. The higher compression ratio will also allow for the contact discontinuity, which is subject to the Rayleigh–Taylor (R–T) instability, to reach much further out to the forward shock. This could create a preferred radial polarization of the magnetic field. With an Adaptive Mesh Refinement MHD code (AMRVAC), we simulate the evolution of SNRs with three different configurations of the initial CSM magnetic field, and look at two different equations of state in order to look at the possible influence of a CR plasma component. The spectrum of CRs can be simulated using test particles, of which we also show some preliminary results that agree well with available analytical solutions.     

A census of high-energy observations of Galactic supernova remnants

We present the first public database of high-energy observations of all known Galactic supernova remnants (SNRs). In Section 1 we introduce the rationale for this work motivated primarily by studying particle acceleration in SNRs, and which aims at bridging the already existing census of Galactic SNRs (primarily made at radio wavelengths) with the ever-growing but diverse observations of these objects at high-energies (in the X-ray and γ$\gamma$-ray regimes). In Section 2 we show how users can browse the database using a dedicated web front–end (http://www.physics.umanitoba.ca/snr/SNRcat). In Section 3 we give some basic statistics about the records we have collected so far, which provides a summary of our current view of Galactic SNRs. Finally, in Section 4, we discuss some possible extensions of this work. We believe that this catalogue will be useful to both observers and theorists, and timely with the synergy in radio/high-energy SNR studies as well as the upcoming new high-energy missions. A feedback form provided on the website will allow users to provide comments or input, thus helping us keep the database up-to-date with the latest observations.     

A preliminary Chandra X-ray spectroscopy of the supernova remnant N132D

We present the preliminary results of a Chandra X-ray study of N132D, a young shell-like supernova remnant (SNR) in the Large Magellanic Cloud. The equivalent width maps of emissions from O, Ne, Mg, Si, and S are provided. Spatially resolved spectral analysis for the small-scale regions were tentatively performed. X-ray spectra of the interior can be described with a single-thermal model. The faint interior regions have lower density, higher temperature above 1 keV than that of bright interior regions. The X-ray spectra along the shell can be phenomenally fitted with either a double-vpshock model or a vpshock + powerlaw model. If the non-thermal component is true, N132D would be listed as another X-ray synchrotron SNR.     

Gamma-ray astronomy and cosmic ray origin problem

We analyse the results of the nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) in order to describe their relevant properties: the remnant dynamics and the characteristics of nonthermal emission produced by CRs. It is shown that the theory fits the existing data in a satisfactory way and that the magnetic field in SNRs is significantly amplified due to efficient acceleration of the nuclear CR component. From the fact that magnetic field amplification occurs in all the young SNRs for which relevant data exist, and given the strong theoretical connection between magnetic field amplification and efficiently accelerating the nuclear CRs, we tentatively conclude that the Galactic SNRs are the source population of the Galactic CRs. Due to high interior magnetic fields in young SNRs the π⁰-decay γ-rays generated by the nuclear CR component as a rule dominate over γ-rays generated by the electron CR component, and the calculated γ-ray flux fits existing data.     

Propagation of cosmic-ray electrons in the Galaxy

We formulate the global propagation model of cosmic-ray electrons including the source region, which is currently considered to be supernova remnants (SNRs). The model is characterized by the escape rate of electrons from SNRs into the interstellar space. It becomes clear that the energy index of the escape rate influences the high energy side of the interstellar spectrum and makes it possible to explain the observed data up to 2 TeV in the case of source spectral index smaller than 2.2 that is expected from the radio spectrum in SNRs. The escape lifetime of electrons in SNRs is also discussed by using the ratio of the radio flux in two regions: SNRs and the Galaxy. The result shows the mean lifetime in SNRs of ∼10⁴ yr around 1 GeV, which corresponds to the SNR age in the Sedov phase.     

Solar system planets observed with Suzaku

Recent results of solar system planets observed with the Japanese X-ray astronomy satellite Suzaku are reviewed. Thanks to the low instrumental background and good energy resolution, X-ray CCDs onboard Suzaku are one of the best probes to study diffuse X-ray emission. An overview of the Suzaku data of Jupiter and Earth is presented, along with preliminary results of Mars. Firstly, diffuse hard X-ray emission is discovered in 1–5 keV at Jovian radiation belts. Its spectrum is represented by a power-law continuum with a photon index of ∼1.4. This emission could originate from inverse-Compton scattering of solar photons by tens MeV electrons. Secondly, variable diffuse soft X-rays are serendipitously found during observations in the directions of the north ecliptic pole and galactic ridge. Good time correlations with the solar wind and emission lines found in the X-ray spectra are firm evidences of a solar wind charge exchange emission with Earth’s exosphere. Thirdly, diffuse X-ray emission from Martian exosphere via the solar wind charge exchange is investigated for the first time at solar minimum. A stringent upper limit on the density of the Martian exosphere is placed from the Suzaku data.     

XMM-Newton observation of Vela shrapnel D

The ROSAT all-sky survey discovered several ‘shrapnels’, showing boomerang structures outside the Vela SNR. We observed the shrapnel D in the eastern limb of the Vela SNR with the XMM-Newton satellite. There is an X-ray bright ridge structure in our FOV running from north to south. There is also an optical bright ridge structure running parallel to that in X-ray about 3′ in the east. These suggest that the shrapnel D is now interacting with an interstellar cloud. Applying the VNEI model to X-ray spectra of various regions, we find that the plasma state of the eastern region of the X-ray ridge is significantly different from that of the western region. The X-ray spectra in the western region can be well fitted with a single temperature component. Abundances of heavy elements are almost uniform, whereas they are heavily overabundant (except Fe): the relative abundances to the solar values are O ∼5, Ne ∼8, Mg ∼8, Fe ∼1. It must have originated from the ejecta of the SN. We find that the plasma in the eastern part of the ridge consists of two temperature components: one component (hot plasma) representing the ejecta while the other (cold plasma) represents the interstellar cloud or swept-up ISM. These two components must have contacted to each other, indicating to form a contact discontinuity. Around northern part of the contact discontinuity, we found wavelike structures of which the typical scales are comparable with that of the Rayleigh–Taylor instability.