Spatial Variation of a Recombining Plasma in the Supernova Remnant W49B

Abstract We have performed 1–12 keV spectral analyses of the recombining plasma associated with the supernova remnant (SNR) W49B using the Suzaku archive data. The analysis results for the whole SNR spectrum indicate that the recombination timescale varies within (5–7) × 10 11 cm −3 s among elements from Mg to Fe and Ni of the RP or that the initial ionization temperatures of the elements vary between 1.6 and 2.7 keV. This paper reports on the results of a more detailed investigation using the latter approach, the multicomponent ionization temperature model. In the overall spectrum, the initial ionization temperatures is estimated to be 2 keV for the lighter elements (Mg, Si) and 5 keV for the heavier elements (Ar and Fe group). For electron cooling scenarios, plasma ionization must proceed at once during a period of high density within about 500 yr after the explosion. The initial ionization temperatures tend to be higher in the east, which would be due to difference of density in circumstellar medium in the early period. On the other hand, current ionization temperatures are found to be spatially uniform, which would be explained by the ionization enhancement scenario by low-energy cosmic rays.