The Puzzles of the Vela Pulsar-Wind Nebula

Details The Puzzles of the Vela Pulsar-Wind Nebula The Puzzles of the Vela Pulsar-Wind Nebula

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008head...10.2106k&link_type=abstract

American Astronomical Society, HEAD meeting #10, #21.06

Astronomy and Astrophysics

Astronomy

Scientific paper

Very few pulsar wind nebulae (PWNe) can be studied at the level of detail comparable to that achieved for the Crab PWN. The nearby Vela PWN is the best candidate for such an in-depth study.
Using Chandra ACIS observations of 2000-2002, we produced a "movie" which shows that not only the NW outer jet, reported by Pavlov et al. (2003), but also the entire bright Vela PWN is remarkably variable. The most dramatic changes occur in the outer arc, the SE inner jet, and the bright knots in the SE part of the inner PWN. On a time scale of 1-3 weeks, the outer arc changes its brightness, shape, and spectrum, the knots move, disappear and appear again, while the SE inner jet changes its brightness and size.
In contrast with the Crab PWN, we see no moving "wisps". The observed changes can be attributed to instabilities in the pulsar wind and to varying density/pressure in the ambient medium.
Deep combined images show that the inner arc is part of a ring, but the pulsar is offset from its plane. The large width of the SE outer "jet" suggests either an intrinsic asymmetry of the SE and NW polar outflows or that the SE jet broadens in a low-pressure cavity behind the moving pulsar. We also found a puzzling "bar" at the base of the inner SE jet, possibly a shock in a polar outflow. An adaptively binned spectral map demonstrates that the inner PWN elements have extremely hard spectra (significantly harder than those of the Crab inner PWN), incompatible with those predicted by the shock acceleration models. Overall, the Vela PWN shows a wealth of puzzling features, different from the Crab; their nature can be understood in a specially designed series of Chandra ACIS observations.

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