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G.G. Pavlov, D. Sanwal, G.P. Garmire (Penn State), V.E. Zavlin, V. Burwitz (MPE, Garching), R.G. Dodson (Univ. of Tasmania)
We report the results of three observations of the Vela pulsar and the surrounding compact X-ray nebula with the High Resolution Camera (HRC) aboard the Chandra X-ray observatory. The superb angular resolution allows one to resolve a complex structure within 2' around the pulsar. It includes a two-sided asymmetrical jet at a position angle of 127\circ, coinciding with the position angle of pulsar's proper motion. The nebula is symmetrical with respect to the jet direction (pulsar's spin axis?) and has a cometary shape, with a bright, narrow (<4'') bow-shaped front edge, of about 40'' maximum size. The pulsar is enveloped by a smaller torus-like nebula of 30'' maximum size.
The observations were carried out 4, 12 and 36 days after the powerful glitch of 2000 January 16, with the HRC-I, HRC-S/LETG and HRC-I, respectively. We put a 3 \sigma upper limit of 1% on the difference between the pulsar's fluxes in the first and third observations. The flux obtained in the second observation does not exceed the fluxes measured with HRC-I by more that 20%. The shape of the light curve does not show statistically significant differences among the three observations. The soft X-ray pulse profile consists of at least three distinct peaks (total pulsed fraction is about 8%). Two peaks are apparently associated with those observed in hard X-rays and gamma-rays and are probably due to nonthermal radiation emitted by relativistic particles ejected from the pulsar. The lowest of the three peaks, and possibly a fourth peak shifted by half a period from the third one and merged with the two higher peaks, may be caused by periodic modulation of the thermal X-ray flux due to hot polar caps, with a temperature of 6 MK and a radius of 100 m. Alternatively, the presence of the additional peak(s) might indicate that the nonthermal radiation is generated at two distinct sites in the pulsar magnetosphere.
This work was partially supported through NASA grants NAG5-6907 and NAG5-7017.
The author(s) of this abstract have provided an email address for comments about the abstract: pavlov@astro.psu.edu