Chandra detection of a synchrotron nebula around the Vela-like pulsar J1016-5857

We report on a 19 ks observation of the pulsar J1016-5857 with the Chandra X-Ray Observatory. This "Velalike'' pulsar has rotation period 107 ms, characteristic age 21 kyr, and spin-down power 2.6 x 10(36) ergs s(-1). A relatively bright, centrally peaked source of radius approximate to25" around the radio pulsar position has a spectrum that is well fitted by an absorbed power law with photon index 1.32 +/- 0.25. We regard this as a newly identified pulsar wind nebula (PWN) that we designate PWN G284.0-1.8. We do not detect the pulsar as either a point X-ray source or a pulsed source in a 55 ks observation with the Rossi X-Ray Timing Explorer. The isotropic PWN luminosity is 3 x 10(32) ergs s(-1) in the 2-10 keV range, for a distance of 3 kpc that is consistent with the measured neutral hydrogen column density. The unpulsed flux from the pulsar is less than 30% of the measured PWN flux. The brightest component of the PWN, near the pulsar, shows extended emission of size similar to2" that may indicate, by analogy with other young pulsars, the wind termination shock. In the Chandra image we also detect a very faint extended structure approximate to1' x 2' in size that is highly asymmetric about the pulsar position. This structure is a good match in width and position angle to the tip of a "finger'' of radio emission that appears to connect to the nearby supernova remnant G284.3-1.8, but we cannot characterize it further with the available data. There is a variable X-ray point source only 1'5 from the pulsar, which we identify using optical spectroscopy as an accreting binary.