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We have completed part of a program to study the X-ray emission properties ofold rotation-powered pulsars with XMM-Newton in order to probe and identify theorigin of their X-radiation. The X-ray emission from these old pulsars islargely dominated by non-thermal processes. None of the observed spectrarequired adding a thermal component consisting of either a hot polar cap orsurface cooling emission to model the data. The X-ray spectrum of PSR 0950+08is best described by a single power law of photon-index1.93^{+0.14}_{-0.12}.Taking optical data from the VLT FORS1 into account abroken power law model is found to describe the pulsar's broadband spectrumfrom the optical to the X-ray band. Temperature upper limits for possiblecontributions from a heated polar cap or the whole neutron star surface areT_{pc} < 0.87 x10^6 K and T_s < 0.48 x 10^6 K, respectively. We also find thatthe X-ray emission from PSR 0950+08 is pulsed with two peaks per rotationperiod. The phase separation between the two X-ray peaks is ~144 degree. Themain radio peak and the trailing X-ray peak are almost phase aligned. Thefraction of X-ray pulsed photons is ~30%. A phase-resolved spectral analysisconfirms the non-thermal nature of the pulsed emission. Detailed pulse profilesimulations constrain the pulsar's emission geometry to be that of an almostorthogonal rotator. The spectral emission properties observed for PSR 0823+26are similar to those of PSR 0950+08. For PSR J2043+2740 we report the firstdetection of X-ray emission. A power law spectrum, or a combination of athermal and a power law spectrum all yield acceptable descriptions of its X-rayspectrum. No X-ray pulses are detected from PSR J2043+2740. A pulsed fractionupper limit is 57%.Comment: Accepted for publication in ApJ on July 15, 2004. The paper with  higher resolution images can be obtained form  ftp://ftp.xray.mpe.mpg.de/people/web/X-ray-emission-from-old-pulsar

Revealing the X‐Ray Emission Processes of Old Rotation‐powered Pulsars:XMM‐NewtonObservations of PSR B0950+08, PSR B0823+26, and PSR J2043+2740