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 Physics , 2000, DOI: 10.1086/318408 Abstract: We present an observational and theoretical study of the optical emission from nonradiative shocks in three supernova remnants: the Cygnus Loop, RCW 86 and Tycho. The spectra of these shocks are dominated by collisionally excited hydrogen Balmer lines which have both a broad component caused by proton-neutral charge exchange and a narrow component caused by excitation of cold neutrals entering the shock. In each remnant we have obtained the broad to narrow flux ratios of the Halpha and Hbeta lines and measured the Halpha broad component width. A new numerical shock code computes the broad and narrow Balmer line emission from nonradiative shocks in partially neutral gas. The Balmer line fluxes are sensitive to Lyman line trapping and the degree of electron-proton temperature equilibration. The code calculates the density, temperature and size of the postshock ionization layer and uses a Monte Carlo simulation to compute narrow Balmer line enhancement from Lyman line trapping. The initial fraction of the shock energy allocated to the electrons and protons (the equilibration) is a free parameter. Our models show that variations in electron-proton temperature equilibration and Lyman line trapping can reproduce the observed range of broad to narrow ratios. The results give 80%-100% equilibration in nonradiative portions of the NE Cygnus Loop (v_shock ~ 300 km/s), 40%-50% equilibration in nonradiative portions of RCW 86 (v_shock ~ 600 km/s) and <~ 20% equilibration in Tycho (v_shock ~ 2000 km/s). Our results suggst an inverse correlation between magnetosonic Mach number and equilibration in the observed remnants.
 Physics , 2002, DOI: 10.1086/341802 Abstract: We use the Chandra X-ray Observatory to analyze interactions of the blast wave and the inhomogeneous interstellar medium on the western limb of the Cygnus Loop supernova remnant. This field of view includes an initial interaction between the blast wave and a large cloud, as well as the encounter of the shock front and the shell that surrounds the cavity of the supernova progenitor. Uniquely, the X-rays directly trace the shock front in the dense cloud, where we measure temperature kT = 0.03 keV. We find kT~0.2 keV in regions where reflected shocks further heat previously-shocked material. Applying one-dimensional models to these interactions, we determine the original blast wave velocity v_bw~330 km/s in the ambient medium. We do not detect strong evidence for instabilities or non-equilibrium conditions on the arcsecond scales we resolve. These sensitive, high-resolution data indicate no exceptional abundance variations in this region of the Cygnus Loop.
 Physics , 2001, DOI: 10.1086/322502 Abstract: With Hubble Space Telescope Wide-Field Planetary Camera 2 observations of the Cygnus Loop supernova remnant, we examine the interaction of an interstellar cloud with the blast wave on physical scales of 10^15 cm. The shock front is distorted, revealing both edge-on and face-on views of filaments and diffuse emission, similar to those observed on larger scales at lower resolution. We identify individual shocks in the cloud of density n~15 cm^-3 having velocity v_s~170 km/s. We also find the morphologically unusual diffuse Balmer-dominated emission of faster shocks in a lower-density region. The obstacle diffracts these shocks, so they propagate at oblique angles with respect to the primary blast wave. The intricate network of diffuse and filamentary H alpha emission arises during the early stage of interaction between the cloud and blast wave, demonstrating that complex shock propagation and emission morphology occur before the onset of instabilities that destroy clouds completely.
 Physics , 1998, DOI: 10.1086/313136 Abstract: We present a complete atlas of the Cygnus Loop supernova remnant in the light of [O III] (5007), H alpha, and [S II] (6717, 6731). Despite its shell-like appearance, the Cygnus Loop is not a current example of a Sedov-Taylor blast wave. Rather, the optical emission traces interactions of the supernova blast wave with clumps of gas. The surrounding interstellar medium forms the walls of a cavity through which the blast wave now propagates, including a nearly complete shell in which non-radiative filaments are detected. The Cygnus Loop blast wave is not breaking out of a dense cloud, but is instead running into confining walls. The interstellar medium dominates not only the appearance of the Cygnus Loop but also the continued evolution of the blast wave. If this is a typical example of a supernova remnant, then global models of the interstellar medium must account for such significant blast wave deceleration.
 Physics , 2014, DOI: 10.1088/0004-637X/784/1/12 Abstract: We present the C III {\lambda}977, O VI {\lambda}{\lambda}1032, 1038 and N IV] {\lambda}1486 emission line maps of the Cygnus Loop, obtained with the newly processed data of Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR; also known as FIMS) mission. In addition, the Si IV+O IV] line complexes around 1400 {\AA} are resolved into two separate emission lines, whose intensity demonstrates a relatively high Si IV region predicted in the previous study. The morphological similarity between the O VI and X-ray images, as well as a comparison of the O VI intensity with the value expected from the X-ray results, indicates that large portions of the observed O VI emissions could be produced from X-ray emitting gas. Comparisons of the far-ultraviolet (FUV) images with the optical and H I 21 cm images, reveal spatial variations of shock-velocity populations and high FUV extinction in the direction of a previously identified H I cloud. By calculating the FUV line ratios for several subregions of the Cygnus Loop, we investigate the spatial variation of the population of radiative shock velocities; and the effects of resonance scattering, X-ray emitting gas, and non-radiative shocks. The FUV and X-ray luminosity comparisons between the Cygnus Loop and the Vela supernova remnant suggest that the fraction of shocks in the early evolutionary stages is much larger in the Cygnus Loop.
 Physics , 2002, DOI: 10.1051/0004-6361:20020787 Abstract: The Cygnus Loop is classified as a middle-aged supernova remnant (SNR) located below the Galactic equator (l=74, b=-8.6) and 770 pc away from us. Its large size and little confusion with Galactic emission makes it an ideal test ground for evolutionary and structural theories of SNRs. New radio continuum mapping of the Cygnus Loop at 2695 MHz with the Effelsberg 100-m telescope provides indications that the Cygnus Loop consists of two separate SNRs. Combining this result with data from the literature we argue that a secondary SNR exists in the south with a recently detected neutron star close to its center. Two interacting SNRs seem to be the best explanation to account for the Cygnus Loop observations at all wavelengths.
 Physics , 2001, DOI: 10.1086/320564 Abstract: We performed spectroscopic X-ray observations of the eastern and northern regions of the Cygnus Loop with the ASCA observatory. The X-ray surface brightness of these regions shows a complex structure in the ROSAT all-sky survey image. We carried out a spatially-resolved analysis for both regions and found that $kT_{\rm e}$ did not increase toward the center region, but showed inhomogeneous structures. Such variation cannot be explained by a blast wave model propagating into a homogeneous interstellar medium. We thus investigated the interaction between a blast wave and an interstellar cloud. Two major emission mechanisms are plausible: a cloud evaporation model and a reflection shock model. In both regions, only a reflection shock model qualitatively explains our results. Our results suggest the existence of a large-scale interstellar cloud. We suppose that such a large-scale structure would be produced by a precursor.
 Physics , 2015, DOI: 10.1017/S1743921315002240 Abstract: Cygnus A, the nearest truly powerful radio galaxy, resides at the centre of a massive galaxy cluster. Chandra X-ray observations reveal its cocoon shocks, radio lobe cavities and an X-ray jet, which are discussed here. It is argued that X-ray emission from the outer regions of the cocoon shocks is nonthermal. The X-ray jets are best interpreted as synchrotron emission, suggesting that they, rather than the radio jets, are the path of energy flow from the nucleus to the hotspots. In that case, a model shows that the jet flow is non-relativistic and carries in excess of one solar mass per year.
 Revista mexicana de astronomía y astrofísica , 2011, Abstract: the estimated brightness of the cygnus loop supernova remnant (snr) at 2720, 1420, 820, 408 and 34.5 mhz is presented. the observations of the continuum radio emission are used to calculate the mean brightness temperatures and surface brightnesses of this loop at the five frequencies in a wide spectral range, using the method we have previously developed for large radio loops. the spectrum for mean temperatures versus frequency between the five frequencies is estimated and the spectral index of the cygnus loop is obtained. also, from our results it can be concluded that the cygnus loop evolves in a low density environment and that the initial energy of the supernova explosion was relatively low. the results obtained confirm the non-thermal origin of the cygnus radio loop and show that our method is applicable to almost all remnants.
 Physics , 2011, Abstract: The estimated brightness of the Cygnus loop supernova remnant (SNR) at 2720, 1420, 820, 408 and 34.5 MHz are presented. The observations of the continuum radio emission are used to calculate the mean brightness temperatures and surface brightnesses of this loop at the five frequencies in wide spectral range, using the method we have previously developed for large radio loops. The spectrum for mean temperatures versus frequency between the five frequencies is estimated and the spectral index of Cygnus loop is also obtained. Also, from our results can be concluded that Cygnus loop evolves in the low density environment and the initial energy of supernova explosion was relatively low. The obtained results confirm non-thermal origin of the Cygnus radio loop and show that our method is applicable to almost all remnants.
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