Chandra pulsar survey (ChaPS)

Taking advantage of the high sensitivity of the Chandra X-ray Observatory's (CXO) Advanced CCD Imaging Spectrometer, we have conducted a snapshot 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, Ė. We find that the obtained limits further increase the extremely large spread in the non-thermal X-ray efficiencies, η ^psr _X = L ^psr _X/Ė, with some of them being now below 10 ^-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 Ė, such that pulsars become more X-ray efficient at Ė ≲ 10 ³⁴-10 ³⁵ergs ^-1. We examine the relationship between the γ-ray luminosity, L ^psr _γ, and Ė, 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 the beaming because the γ-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 _γ(Ė) dependence at Ė ∼ 10 ³⁵ergs ^-1, with lower-Ė pulsars becoming less γ-ray efficient. We also examine the distance-independent L ^psr _γ/L ^psr _X ratio as a function of for a sample of γ-ray pulsars observed by CXO and find that it peaks at Ė ∼ 10 ³⁵ ergs ^-1, 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.