Observability and diagnostics in the X-ray band of shock-cloud interactions in supernova remnants

Abstract

Context. X-ray emitting features originating from the interaction of supernova shock waves with small interstellar gas clouds are revealed in many X-ray observations of evolved supernova remnants (e.g., Cygnus Loop and Vela), but their interpretation is not straightforward. Aims. We develop a self-consistent method for the analysis and interpretation of shock-cloud interactions in middle-aged supernova remnants, which can provide the key parameters of the system and the role of relevant physical effects such as thermal conduction, without the need to perform ad-hoc numerical simulations and bother about morphology details. Methods. We explore all the possible values of the shock speed and cloud density contrast relevant to middle-aged SNRs with a set of hydrodynamic simulations of shock-cloud interaction including the effects of thermal conduction and radiative cooling. From the simulations, we synthesize spatially and spectrally resolved focal-plane data as they would be collected with XMM-Newton/EPIC, an X-ray instrument commonly used in these studies. Results. We develop and calibrate two diagnostic tools, the first based on the mean photon energy versus count-rate scatter plot and the second on the spectral analysis of the interaction region, that can be used to highlight the effects of thermal conduction and to derive the shock speed in case of efficient conduction at work. These tools can be used to ascertain information from X-ray observations, without the need to develop detailed and ad-hoc numerical models for the interpretation of the data.

The origin of the X-ray-emitting plasma in the eastern edge of the Cygnus Loop

“…Therefore, the regions were also selected as homogeneous as possible in the map to avoid large spread of spectral properties. The spectra from the regions surrounding shocked clouds are sensitive to the physical state of the interaction; Miceli et al (2006) and Orlando et al (2010) found that the spectral analysis of regions selected in this way is an efficient diagnostic tool to investigate the role of thermal conduction (see ).…”

“…The relationship between the median photon energy and the count rate ( R ) is critically influenced by different physical processes such as thermal conduction in the shock–cloud interaction and can provide important information (Orlando et al 2010). In this framework, we derived the versus R scatter plots for each of the four couples of regions (Fig.…”

“…1a) and the filaments observed in the optical band (Danforth et al 2001) strongly indicate that in the XA region the blast wave of the Cygnus Loop is encountering a large‐scale inhomogeneity of the ISM. In such interacting region, the X‐ray‐emitting plasma can be typically described with two thermal components associated with two phases of ISM swept up by the shock, as shown in theoretical models (Miceli et al 2006; Orlando et al 2006, 2010). In this scenario, the two‐temperature components found in our spectral analysis probably indicate two thermal phases of ISM: (i) the shocked dense cloud material and (ii) the surrounding corona.…”

“…Orlando et al (2005) and Orlando et al (2006) examined the shock–cloud interaction in different physical regimes by using a detailed hydrodynamic model, including thermal conduction and radiative losses, and synthesizing the relevant X‐ray emission. Based on these works, Orlando et al (2010) proposed a diagnostic tool to derive quickly the efficiency of thermal conduction from the results of the X‐ray data analysis, without the need of running a time‐consuming ad hoc hydrodynamical model. By using such advanced method, the origin of X‐rays in the Cygnus Loop can be investigated to derive a better understanding of the shock–cloud interaction.…”

Soft X-ray emission in kink-unstable coronal loops

“…A correction is applied to this term, so that the conductive heat flux becomes independent of ∇T for extremely large temperature A37, page 2 of 16 gradients (see, e.g., Orlando et al 2010;West et al 2008). This correction relies on the definition of the saturation flux q sat…”