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تسجيل مستخدم جديدResolved shock structure of the Balmer-dominated filaments in Tychos supernova remnant: Cosmic-ray precursor?
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We report on the results from H{alpha} imaging observations of the eastern limb of Tychos supernova remnant (SN1572) using the Wide Field Planetary Camera 2 on the Hubble Space Telescope. We resolve the detailed structure of the fast, collisionless shock wave into a delicate structure of nearly edge-on filaments. We find a gradual increase of H{alpha} intensity just ahead of the shock front, which we interpret as emission from the thin (~1) shock precursor. We find that a significant amount of the H{alpha} emission comes from the precursor and that this could affect the amount of temperature equilibration derived from the observed flux ratio of the broad and narrow H{alpha} components. The observed H{alpha} emission profiles are fit using simple precursor models, and we discuss the relevant parameters. We suggest that the precursor is likely due to cosmic rays and discuss the efficiency of cosmic-ray acceleration at this position.
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We present a time-dependent cosmic-ray modified shock model for which the calculated H-alpha emissivity profile agrees well with the H-alpha flux increase ahead of the Balmer-dominated shock at knot g in Tychos supernova remnant, observed by Lee et a
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We present an Ha spectral observation of a Balmer-dominated shock on the eastern side of Tychos supernova remnant using the Subaru Telescope. Utilizing the High Dispersion Spectrograph (HDS), we measure the spatial variation of the line profile betwe
en preshock and postshock gas. Our observation clearly shows a broadening and centroid shift of the narrow-component postshock Ha line relative to the Ha emission from the preshock gas. The observation supports the existence of a thin precursor where gas is heated and accelerated ahead of the shock. Furthermore, the spatial profile of the emission ahead of the Balmer filament shows a gradual gradient in the Ha intensity and line width ahead of the shock. We propose that this region (~10^16 cm) is likely to be the spatially resolved precursor. The line width increases from ~30 up to ~45 km/s, and its central velocity shows a redshift of ~5 km/s across the shock front. The characteristics of the precursor are consistent with a cosmic-ray precursor, although the possibility of a fast neutral precursor is not ruled out.
We present high-resolution long-slit spectroscopy of a Balmer-dominated shock in the northeastern limb of the Cygnus Loop with the Subaru high dispersion spectrograph. By setting the slit angle along the shock normal, we investigate variations of the
flux and profile of the H-alpha line from preshock to postshock regions with a spatial resolution of about 4 times 10^{15} cm. The H-alpha line profile can be represented by a narrow (28.9+/-0.7 km/s) Gaussian in a diffuse region ahead of the shock, i.e., a photoionization precursor, and narrow (33.1+/-0.2 km/s) plus broad (130-230 km/s) Gaussians at the shock itself. We find that the width of the narrow component abruptly increases up to 33.1+/-0.2 km/s, or 38.8+/-0.4 km/s if we eliminate projected emission originating from the photoionization precursor, in an unresolved thin layer (< 4 times 10^{15} cm at a distance of 540 pc) at the shock. We show that the sudden broadening can be best explained by heating via damping of Alfven waves in a thin cosmic-ray precursor, although other possibilities are not fully ruled out. The thickness of the cosmic-ray precursor in the Cygnus Loop (a soft gamma-ray emitter) is an order of magnitude thinner than that in Tychos Knot g (a hard gamma-ray emitter), which may be caused by different energy distribution of accelerated particles between the two sources. In this context, systematic studies might reveal a positive correlation between the thickness of the cosmic-ray precursor and the hardness of the cosmic-ray energy distribution.
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