Chandra observations of the old pulsar PSR B1451-68

We present 35ks Chandra ACIS observations of the 42Myr old radio pulsar PSR B1451-68. A point source is detected 0″.32 ± 0″.73 from the expected radio pulsar position. It has ∼200 counts in the 0.3-8keV energy range. We identify this point source as the X-ray counterpart of the radio pulsar. PSR B1451-68 is located close to a Two Micron All Sky Survey point source for which we derive 7% as the upper limit on the flux contribution to the measured pulsar X-ray flux. The pulsar spectrum can be described by either a power-law model with photon index Γ = 2.4^+0.4 _-0.3 and a unrealistically high absorbing column density N _H = (2.5 ^+1.2 _{- 1.3}) × 10²¹cm^-2, or by a combination of a kT = 0.35^+0.12 _{- 0.07} keV blackbody and a Γ = 1.4 ± 0.5 power-law component for N ^DM _H = 2.6 × 10²⁰cm^-2, estimated from the pulsar dispersion measure. At the parallactic, a Lutz-Kelker bias corrected distance of 480pc, the non-thermal X-ray luminosities in the 0.3-8keV energy band are either L ^nonth _{0.3-8 keV} = (11.3 ± 1.7) × 10²⁹ergs^-1 or L ^nonth _{0.3-8 keV} = (5.9^+4.9 _{- 5.0}) × 10 ²⁹ergs^-1, respectively. This corresponds to non-thermal X-ray efficiencies of either or ν^nonth_{0.38 keV}= L ^nonth_0.38keV/Ė ∼ 5 × 10^?3 or 10^-3, respectively.