Chandra pulsar survey (ChaPS)
  Taking advantage of the high sensitivity of the Chandra Advanced CCD Imaging Spectrometer, we have conducted a snap-shot survey of pulsars previously undetected in X-rays. We detected 12 pulsars and established deep flux limits for 11 pulsars. Using these new results, we revisit the relationship between the X-ray luminosity, L_psr_x, and spin-down power, Edot. We find that the obtained limits further increase the extremely large spread in the non-thermal X-ray efficiencies, eta_psr_x=L_psr_x/Edot, with some of them being now below 1e-5. Such a spread cannot be explained by poorly known distances or by beaming of pulsar radiation. We also find evidence of a break in the dependence of L_psr_x on Edot, such that pulsars become more X-ray efficient at Edot<~ 1e34-1e35 erg/s. We examine the relationship between the gamma-ray luminosity, L_psr_g, and Edot, which exhibits a smaller scatter compared to that in X-rays. This confirms that the very large spread in the X-ray efficiencies cannot be explained just by beaming because the gamma-ray emission is generally expected to be beamed stronger than the X-ray emission. Intriguingly, there is also an indication of a break in the L_psr_g(Edot) dependence at Edot~1e35 erg/s, with lower-Edot pulsars becoming less gamma-ray efficient. We also examine the distance-independent L_psr_f/L_psr_x ratio as a function of Edot for a sample of gamma-ray pulsars observed by Chandra and find that it peaks at Edot~1e35 erg/s, showing that the breaks cannot originate from poorly measured distances. We discuss the implications of our findings for existing models of magnetospheric emission and venues for further exploration. 
Oleg Kargaltsev, Martin Durant, George G. Pavlov, and Gordon Garmire
astro-ph.HE