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We examined the X-ray and radio spatial structure at the eastern ear of the W 50/SS 433 system to clarify a characteristic feature of the termination region of the SS 433 jet, and found that a hot spot ahead of the filament structure, which is considered to be a terminal shock of the SS 433 eastern jet, is clearly different from a single point source. The detailed spatial structure of the X-ray emission is finely resolved by Chandra observations, showing that there are two sources. By comparing the point-spread function of Chandra with the radial profiles of the two sources, the northern one is clearly more extended than a point source while the other seems marginally extended. Since there are no point sources nearby, the northern hot spot is likely a localized diffuse source. The northern hot spot spatially corresponds to the peak of the radio emission. Its spatial correlation is confirmed by an X-ray image using XMM-Newton. The X-ray spectra of the two sources are reproduced by a single absorbed power-law but the column density of the northern part is larger by a factor of ∼3. When a radiation model comprising synchrotron emission and inverse Compton emission is applied to the spectral energy distribution of the northern hot spot, the emission from this spot can be explained by the radiation from an electron population accelerated up to 30 TeV in a magnetic field strength of B ≲ 50 μG. This model also agrees with the radio and X-ray data, as well as the upper limit of gamma-ray emission obtained by the Fermi satellite.

The origin of the jet-like structures observed in Cassiopeia A is still unclear, although it seems to be related to its explosion mechanism. X-ray observations of the characteristic structures could provide us useful information on the explosive nucleosynthesis via the observation of elements, which is a unique approach to understand its origin. We here report the discovery of shocked stable Ti, which is produced only at the inner region of exploding stars, in the northeast jet of Cassiopeia A using the 1-Ms deep observation with the Chandra X-ray observatory. The observed Ti coexists with other intermediate-mass elements (e.g. Si, S, Ar, Ca) and Fe at the tip of the X-ray jet structure. We found that its elemental composition is well explained with the production by the incomplete Si burning regime, indicating that the formation process of the jet structure was sub-energetic at the explosion (the peak temperature during the nuclear burning must be $\lesssim$ 5$\times$10$^{9}$ K at most). Thus, we conclude that the energy source that formed the jet structure was not the primary engine for the supernova explosion. Our results are useful to limit the power of the jet-structure formation process, and a weak jet mechanism with low temperature may be needed to explain it., Comment: Accepted for publication in PASJ, 9 pages, 5 figures, 2 tables

We present X-ray analysis of the ejecta of supernova remnant G350.1$-$0.3 observed with Chandra and Suzaku, and clarify the ejecta's kinematics over a decade and obtain a new observational clue to understanding the origin of the asymmetric explosion. Two images of Chandra X-ray Observatory taken in 2009 and 2018 are analyzed in several methods, and enable us to measure the velocities in the plane of the sky. A maximum velocity is 4640$\pm$290 km s$^{-1}$ (0.218$\pm$0.014 arcsec yr$^{-1}$) in the eastern region in the remnant. These findings trigger us to scrutinize the Doppler effects in the spectra of the thermal emission, and the velocities in the line-of-sight direction are estimated to be a thousand km s$^{-1}$. The results are confirmed by analyzing the spectra of Suzaku. Combining the proper motions and line-of-sight velocities, the ejecta's three-dimensional velocities are $\sim$3000-5000 km s$^{-1}$. The center of the explosion is more stringently constrained by finding the optimal time to reproduce the observed spatial expansion. Our findings that the age of the SNR is estimated at most to be 655 years, and the CCO is observed as a point source object against the SNR strengthen the 'hydrodynamical kick' hypothesis on the origin of the remnant., Comment: ApJ accepted. 12 pages, 6 figures

The supernova remnant (SNR) RX J1713.7$-$3946 is one of the best-studied accelerators of cosmic rays because of its strong nonthermal X-ray and gamma-ray radiation. We have analyzed accumulated \chandra\ observations with a total exposure time of $\sim$266 ks in the northwest rim of RX J1713.7$-$3946. We detect a substantially large number of point-like sources, referred to as ``hotspots'', which are likely associated with the remnant. The spectra of the hotspots are well described by an absorbed power-law model. The spectral properties ($10^{21}\ \mathrm{cm^{-2}}\lesssim N_H \lesssim 10^{23}\ \mathrm{cm^{-2}}$ and $ 0.5\lesssim \Gamma \lesssim 6$) are different from diffuse X-ray emission in RX J1713.7$-$3946, and the harder hotspot tends to have the larger $N_H$. We also confirm yearly and monthly variabilities of flux for some hotspots. We propose that RX J1713.7$-$3946 is embedded in a complex surroundings where some dense molecular clumps and cores exist inside a wind-blown cavity, and that the hotspot traces synchrotron emission caused by an interaction of shock waves of the SNR and dense molecular cores with a number density of $10^{5}-10^{7}~ \mathrm{cm}^{-3}$. The X-ray radiation of the hotspot might be emitted from both primary electrons accelerated at the shocks and secondary electrons produced by the interaction of accelerated protons with the cores., Comment: 15 pages, 8 figures, 3 tables; Accepted for publication in ApJ

The astrophysical journal / 1 Part 1 877(2), 96 - (2019). doi:10.3847/1538-4357/ab1b29, The shock waves of supernova remnants (SNRs) are prominent candidates for the acceleration of the Galactic cosmic rays. SNR RX J1713.7−3946 is one well-studied particle accelerator in our Galaxy because of its strong nonthermal X-ray and gamma-ray radiation. We have performed Nuclear Spectroscopic Telescope Array (3–79 keV) observations of the northwest rim of RX J1713.7−3946, which is the brightest part in X-ray and has a shock speed of about 4000 km s−1. The spatially resolved X-ray emission from RX J1713.7−3946 is detected up to 20 keV for the first time. The hard X-ray image in 10–20 keV is broadly similar to the soft-band image in 3–10 keV. The typical spectrum is described by power-law model with exponential cutoff with the photon index Γ = 2.15 and the cutoff energy ε c = 18.8 keV. Using a synchrotron radiation model from accelerated electrons in the loss-limited case, the cutoff energy parameter ranges from 0.6–1.9 keV, varying from region to region. Combined with the previous measurement of the shock speed, the acceleration of electrons is close to the Bohm-limit regime in the outer edge, while the standard picture of accelerated particles limited by synchrotron radiation in SNR shock is not applicable in the inner edge and the filamentary structure., Published by Institute of Physics Publ., London