Re-identification of G35.6−0.4 as a supernova remnant

G35.6−0.4 is an extended radio source in the Galactic plane which has previously been identified as either a supernova remnant or an H  ii region. Observations from the Very Large Array Galactic Plane Survey at 1.4 GHz with a resolution of 1 arcmin allow the extent of G35.6−0.4 to be defined for the first time. Comparison with other radio survey observations show that this source has a non-thermal spectral index, with   S ∝ν^{−0.47±0.07}  . G35.6−0.4 does not have obvious associated infrared emission, so it is identified as a Galactic supernova remnant, not an H  ii region. It is  ≈15 × 11 arcmin²  in extent, showing partial limb brightening.     

On the manifestation of Richtmyer-Meshkov instability in an inhomogeneous interstellar medium with radiative cooling

We numerically simulate the evolution of the plane two-dimensional deformations of a contact discontinuity that is impulsively accelerated by a shock wave. We take into account the effects of radiative cooling and perturbation scale lengths on the dynamics and shape of the forming density inhomogeneities. For moderately intense shocks in a stellar wind and for strong shocks from a supernova, we show that the radiative cooling processes do not affect significantly the growth rate of the initial perturbations and the total mass of the forming condensations. However, the density of the matter compressed by the transmitted shock wave increases dramatically. At the same time, the contribution from long-wavelength perturbations to the deformation of the contact surface decreases significantly. In the case of shock propagation from a supernova, the initial conditions have been found to be a factor that can affect the morphology of the shocked interstellar medium.     

Morphological and spectral studies of the shell-type supernova remnants RX J1713.7–3946 and RX J0852.0–4622 with H.E.S.S.

In 2004 and 2005, the shell-type supernova remnants RX J1713.7–3946 and RX J0852.0–4622 were observed and detected with the complete H.E.S.S. array, a system of four Imaging Cherenkov Telescopes located in Namibia and dedicated to the observations of γ-rays above 100 GeV. The energy spectra of these two sources have been measured over a wide energy range and revealed an integral flux above 1 TeV similar to that of the Crab Nebula. Their morphologies were resolved with high accuracy with H.E.S.S. and exhibit a striking correlation with the X-ray images, thereby pioneering a technique of unambiguously identifying spatially extended γ-ray sources. The results of the observations will be presented. Similarities and differences between these two sources will be pointed out as well as possible implications. M. Lemoine-Goumard, F. Aharonian, D. Berge, B. Degrange, D. Hauser, N. Komin, O. Reimer, U. Schwanke for the H.E.S.S. Collaboration     

Effects of boundary conditions and viscous energy dissipation on carbon burning in thermonuclear supernova models

Based on a one-dimensional hydrodynamic model, we investigate carbon burning in a thermonuclear type-Ia supernova in the approximation of unsteady convection. The relatively broad range of convective parameters, 1×10^?3≤α_c≤2×10^?3, in which delayed detonation from the edge takes place was found to be preserved only for cases with a low boundary temperature at the presupernova stage, T _b ^(PS) = 6.4 × 10⁶ K, and with a high envelope mass, m_ex ? 2 × 10^?3M_⊙. In cases with a more realistic temperature, T _b ^(PS) = 2 × 10⁸ K, which corresponds to helium burning in the shell source, and with a lower mass m_ex, delayed detonation from the edge takes place only at α_c = 2 × 10^?3, while at α_c = 1 × 10^?3, numerous model pulsations occur during t?500 s. Artificial viscosity is shown to give a determining contribution to the increase in entropy in outer model shells, which is caused by the generation of weak shock waves during pulsations. We also show that the entropies calculated by two independent methods are equal.     

Neutral hydrogen absorption against supernova remnants in M82

We present MERLIN neutral hydrogen absorption measurements against supernova remnants in the central starburst region of M82 with an angular resolution of ∼ 0.4 arcsec. We detect H  I absorption or set significant upper limits against 33 supernova remnants from which we have been able to deduce column densities. Hence, using these measurements, we are able to probe the neutral hydrogen distribution and dynamics of the interstellar medium in M82 along 33 lines of sight on linear scales of order 1 pc.   Our results show column densities ranging from <1.6 to >30 × 10²¹ atom cm⁻² with the highest values seen towards the edge of the 250-pc 'ring'. The absorption velocities show a gradient of 7.3 ± 4 km s⁻¹ arcsec⁻¹, consistent with rotation parameters of this 'ring' inferred from other measurements. The absorption velocities against individual remnants show deviations of typically 30 km s⁻¹ from simple solid body rotation, and a number show multiple velocity absorption features. Although some of these deviations may be the result of the remnants being embedded at different depths within the neutral gas, the velocities cannot be explained by a simple rotating ring.     

Neutral hydrogen absorption observations of the central region of NGC 3628

Using MERLIN with 0.2-arcsec resolution we have observed neutral hydrogen absorption against the central region of the starburst galaxy NGC 3628. The central region resolves into ∼16 continuum components at 1.4 GHz. From comparison with published 15-GHz data, we infer that these components are supernova remnants, although three components may be consistent with a weak active galactic nucleus. Neutral hydrogen absorption is seen against the continuum emission with column densities ∼10²² cm⁻². The absorption appears to be from two separate absorbing structures. Assuming a simple morphology, the main velocity structure can be attributed to a ring of neutral gas with a radius 130 pc rotating around a central starburst with a velocity gradient of 1270 km s⁻¹ kpc⁻¹. From simple assumptions, the mass interior to this ring is 0.9 × 10⁹ M_⊙. The second absorption structure may represent outflow from the starburst region or a large-scale galactic structure. Alternatively the absorption structure may be non-axisymmetric, such as a bar.