Wind-swept clouds and possible triggered star formation associated with the supernova remnant G357.7+0.3

We present evidence for interaction between the supernova remnant (SNR) G357.7+0.3 and nearby molecular clouds, leading to the formation of wind-swept structures and bright emission rims. These features are not observed at visual wavelengths, but are clearly visible in mid-infrared mapping undertaken using the Spitzer Space Telescope . Analysis of one of these clouds, the bright cometary structure G357.46+0.60, suggests that it contains strong polycyclic aromatic hydrocarbon emission features in the 5.8 and 8.0 μm photometric bands, and that these are highly variable over relatively small spatial scales. The source is also associated with strong variations in electron density; a far-infrared continuum peak associated with dust temperatures of ∼30 K; and has previously been observed in the 1720 MHz maser transition of OH, known to be associated with SNR shock excitation of interstellar clouds. This source also appears to contain a young stellar object (YSO) within the bright rim structure, with a steeply rising spectrum between 1.25 and 24 μm. If the formation of this star has been triggered recently by the SNR, then YSO modelling suggests a stellar mass  ∼5–10 M_⊙  , and luminosity   L _YSO∼10²–2 × 10³ L_⊙  .
Finally, it is noted that a further, conical emission region appears to be associated with the Mira V1139 Sco, and it is suggested that this may represent the case of a Mira outflow interacting with a SNR. If this is the case, however, then the distance to the SNR must be ∼half of that determined from CS   J = 2–1  and 3–2 line radial velocities.     

Some properties of synchrotron radio and inverse-Compton gamma-ray images of supernova remnants

The synchrotron radio maps of supernova remnants (SNRs) in a uniform interstellar medium and interstellar magnetic field (ISMF) are analysed, allowing for different 'sensitivity' of the injection efficiency to the obliquity of the shock. The very-high-energy γ-ray maps arising from inverse Compton processes are also synthesized. The properties of images in these different wavelength bands are compared, with particular emphasis on the location of the bright limbs in bilateral SNRs. Recent High-Energy Stereoscopic System (HESS) observations of SN 1006 show that the radio and inverse Compton γ-ray limbs coincide, and we found that this may happen if (i) injection is isotropic but the variation of the maximum energy of electrons is rather fast to compensate for differences in the magnetic field, or (ii) the obliquity dependence of injection (either quasi-parallel or quasi-perpendicular) and the electron maximum energy are strong enough to dominate the magnetic field variation. In the latter case, the obliquity dependences of the injection and the maximum energy should not be opposite. We argue that the position of the limbs alone, and even their coincidence in radio, X-rays and γ-rays, as discovered by HESS in SN 1006, cannot be conclusive as regards the dependence of the electron injection efficiency, the compression/amplification of the ISMF and the electron maximum energy on the obliquity angle.     

The Influence of a New Model of Progenitor Star on Supernova Explosion

By adopting the progenitor model proposed by Woosley in 2002 and using the program WZYW89, the process of explosion of type II supernovae with masses of 11−40M_⊙ is numerically simulated. The results of computation reveal that this new model can in different degrees affect the collapse and explosion of type II supernovae as well as the propagation of shock waves. Besides, the definitions of the primary energy of shock waves are also discussed.     

New observations of the only supernova remnant in the galaxy IC 1613

We present new results of our kinematic study of the supernova remnant S8 in the galaxy IC 1613. Based on our observations at the 6-m Special Astrophysical Observatory telescope with the two-dimensional MPFS spectrograph and the SCORPIO focal reducer in the mode of a scanning Fabry-Perot interferometer, we have determined the expansion velocity of the bright optical nebula. Analysis of the 21-cm VLA radio observations for the galaxy confirms our previously suggested model for a supernova explosion in a cavity surrounded by a dense HI shell and a collision of S8 with the shell wall.     

The brightness of the galactic radio loops at 1420 MHz: Some indications for the existence of Loops V and VI

In this article we use 1420 MHz data to demonstrate the likely reality of Galactic radio Loops V and VI. We further estimate distances and spectral indices for both these and the four main radio loops. In the cases of Loops I–IV, radio spectral indices are calculated from the mean brightnesses at 1420 and 820/404 MHz. The spectral indices of Loops V and VI are obtained from T –T plots between 1420 and 408 MHz. Using the supernova remnant (SNR) hypothesis for the origin of radio loops, distances are calculated from the surface brightnesses and the angular diameters at 1420 MHz. We also study how results for brightnesses and distances of radio loops agree with current theories of SNR evolution. For this purpose, the ambient density and initial explosion energy of the loops are discussed. We also discuss applications of different Σ–D relations. The results obtained confirm a non‐thermal origin and nearby locations for the Galactic radio loops. Therefore, we have indications that they are very old SNRs that evolve in low ambient densities, with high initial explosion energies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High Spatial Resolution X-Ray Spectroscopy of Cas A with Chandra

We present high spatial resolution X-ray spectroscopy of the supernova remnant Cassiopeia A with the Chandra observations. The X-ray emitting region of this remnant was divided into 38 × 34 pixels of 10″× 10″ each. Spectra of 960 pixels were created and fitted with an absorbed two component non-equilibrium ionization model. From the results of the spectral analysis we obtained maps of absorbing column density, temperatures, ionization ages, and the abundances of Ne, Mg, Si, S, Ca and Fe. The Si, S and possibly Ca abundance maps show obvious jet structures, while Fe does not follow the jet but seems to be distributed perpendicular to it. The abundances of Si, S and Ca show tight correlations between one another over a range of about two dex. This suggests that they are ejecta from explosive Oburning and incomplete Si-buming. Meanwhile, the Ne abundance is well correlated with that of Mg, indicating them to be the ashes of explosive C/Ne burning. The Fe abundance is positively correlated with that of Si when the latter is lower than 3 times the solar value, and is negatively correlated when higher. We suggest that such a two phase correlation is due to the different ways in which Fe was synthesized.     

Circumstellar Na I and Ca II absorption lines of type Ia supernovae in the symbiotic scenario

The formation of circumstellar Na I and Ca II resonance absorption lines in a type Ia supernova is studied in the case where the supernova explodes in a binary system with a red giant. The model suggests a spherically symmetric wind and takes into account the nonstationary ionization and heating of the wind by X rays from the shock wave and by gamma rays from radioactive ⁵⁶Ni decay. For wind densities typical of a red giant, the expected optical depth of the wind in Na I lines is shown to be too small (τ < 10^?3) for their detection. Under the same conditions, the optical depth of the predicted Ca II 3934 Å absorption line is sufficient for its detection (τ > 0.1). It is concluded that the Na I and Ca II absorption lines detected in SN 2006X could not be formed in the red giant wind and are most likely related to clouds at distances exceeding the dust evaporation radius (r > 10¹⁷ cm). An upper limit for the rate of mass loss through a stationary wind with velocity u has been obtained from the absence of Ca II absorption lines in SN 2006X unrelated to the similar Na I components: ? < 10^?8 (u/10 km s^?1) M _⊙ yr^?1.     

Dynamo coefficients from local simulations of the turbulent ISM

Observations in polarized emission reveal the existence of large‐scale coherent magnetic fields in a wide range of spiral galaxies. Radio‐polarization data show that these fields are strongly inclined towards the radial direction, with pitch angles up to 35° and thus cannot be explained by differential rotation alone. Global dynamo models describe the generation of the radial magnetic field from the underlying turbulence via the so called α ‐effect. However, these global models still rely on crude assumptions about the small‐scale turbulence. To overcome these restrictions we perform fully dynamical MHD simulations of interstellar turbulence driven by supernova explosions. From our simulations we extract profiles of the contributing diagonal elements of the dynamo α ‐tensor as functions of galactic height. We also measure the coefficients describing vertical pumping and find that the ratio between these two effects has been overestimated in earlier analytical work, where dynamo action seemed impossible. In contradiction to these models based on isolated remnants we always find the pumping to be directed inward. In addition we observe that depends on whether clustering in terms of superbubbles is taken into account. Finally, we apply a test field method to derive a quantitative measure of the turbulent magnetic diffusivity which we determine to be ∼2 kpckms^–1. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

超新星爆发与暗晕中重子物质的丢失

讨论了在以冷暗物质为主的宇宙中,超新星爆发对矮星系演化的反馈作用。建立了星系的质量丢失模型,提出了理论模型与观测进行比较的方法。对数值计算结果的理论分析表明,当星系外围存在一个暗物质晕时,由超新星爆发引起的质量丢失虽然受到了极大的限制,却不像人们预期的那么困难。如果假定星系的形成红移为ｚ＝２～８,那么,在所选取的参数范围内,理论计算和观测结果是相符合的。这种定性上的符合显示出,星系的质量越小,它们就形成得越早．