2013ApJ...768..182K

Using the unprecedented spectral resolution of the reflection grating spectrometer (RGS) on board XMM-Newton, we reveal dynamics of X-ray-emitting ejecta in the oxygen-rich supernova remnant Puppis A. The RGS spectrum shows prominent K-shell lines, including O VII Heα forbidden and resonance, O VIII Lyα, O VIII Lyβ, and Ne IX Heα resonance, from an ejecta knot positionally coincident with an optical oxygen-rich filament (the so-called Ω filament) in the northeast of the remnant. We find that the line centroids are blueshifted by 1480±140±60 km/s (the first and second term errors are measurement and calibration uncertainties, respectively), which is fully consistent with that of the optical Ω filament. Line broadening at 654 eV (corresponding to O VIII Lyα) is obtained to be σ ≲ 0.9 eV, indicating an oxygen temperature of ≲ 30 keV. Analysis of XMM-Newton MOS spectra shows an electron temperature of ∼0.8 keV and an ionization timescale of ∼2x10¹⁰/cm3 s. We show that the oxygen and electron temperatures as well as the ionization timescale can be reconciled if the ejecta knot was heated by a collisionless shock whose velocity is ∼600-1200 km/s and was subsequently equilibrated due to Coulomb interactions. The RGS spectrum also shows relatively weak K-shell lines of another ejecta feature located near the northeastern edge of the remnant, from which we measure redward Doppler velocities of 650±70±60 km/s.