On Dynamics and Spectra of Fine Spatial Structures in the Vela Pulsar Wind Nebula

Evolution of X-ray surface brightness and spectra of fine spatial structures in the Vela pulsar wind nebula (PWN) are studied. Variability of morphology and the spectrum of a small-scale structure at the base of the southern jet of the nebula – a bright transverse bar is investigated for the first time. The size of the bar located within 4″–5″ from the Vela pulsar is ∼ 4.5″ × 1.5″. It is shown that brightness, shapes, and positions of the bar and the southern jet base vary on the timescale of 1–2 weeks, the bar can disappear and emerge again within 10 days. The power-law photon index of the jet base is much harder than that of the bar, 1.20 ± 0.12 vs 1.65 ± 0.15. The latter index is close to 1.6, a typical value for synchrotron emission of electrons accelerated at an ultrarelativistic shock. We speculate that bright blobs seen on both sides of the southern jet base may have the same nature as the bright blobs in the Crab PWN, which are believed to mark the position of the termination shock of the pulsar wind. (paper)