2009ApJ...702..433K

PSR J1906+0746 is a young radio pulsar (τ = 112 kyr, P = 144 ms) in a tight binary (P_orb= 3.98 hr) with a compact high-mass companion (M_comp≃ 1.36 M_☉), at the distance of about 5 kpc. We observed this unique relativistic binary with the Chandra Advanced CCD Imaging Spectrometer detector for 31.6 ks. Surprisingly, not a single photon was detected within the 3'' radius from the J1906+0746 radio position. For a plausible range of hydrogen column densities, n_H= (0.5-1)x10²²/cm2, the nondetection corresponds to the 90% upper limit of (3-5)x10³⁰ erg/s on the unabsorbed 0.5-8 keV luminosity for the power-law model with Γ = 1.0-2.0, and ∼10³² erg/s on the bolometric luminosity of the thermal emission from the neutrons star surface. The inferred limits are the lowest known for pulsars with spin-down properties similar to those of PSR J1906+0746. We have also tentatively detected a puzzling extended structure which looks like a tilted ring with a radius of 1'.6 centered on the pulsar. The measured 0.5-8 keV flux of the feature, ~3.1x10^–14 erg/cm2/s, implies an unabsorbed luminosity of 1.2x10³² erg/s (4.5x10^–4 of the pulsar's {dot}E) for n_H= 0.7x10²²/cm2. If the ring is not a peculiar noise artifact, the pulsar wind nebula around an unusually underluminous pulsar would be the most plausible interpretation.