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, LpsrX, and spin-down power, E-dot . We find that the obtained limits further increase the extremely large spread in the non-thermal X-ray efficiencies, ηpsrX = LpsrX/ E-dot , 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 LpsrX on E-dot , such that pulsars become more X-ray efficient at E-dot ∼<1034-1035 erg s–1. We examine the relationship between the γ-ray luminosity, Lpsrγ, and E-dot , 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 Lpsrγ ( E-dot ) dependence at E-dot ∼1035 erg s–1, with lower- E-dot pulsars becoming less γ-ray efficient. We also examine the distance-independent Lpsrγ/LpsrX ratio as a function of E-dot for a sample of γ-ray pulsars observed by CXO and find that it peaks at E-dot ∼1035 erg s–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.