Extended emission from the PSR B1259-63/SS 2883 binary detected with Chandra

PSR B1259-63 is a middle-aged radio pulsar (P = 48ms, τ = 330 kyr, and erg s^-1) in an eccentric binary (P _orb = 3.4 yr, e = 0.87) with a high-mass Be companion, SS 2883. We observed the binary near apastron with the Chandra ACIS detector on 2009 May 14 for 28 ks. In addition to the previously studied point-like source at the pulsar's position, we detected extended emission on the south-southwest side of this source. The point-like source spectrum can be described by the absorbed power-law model with the hydrogen column density N _H = (2.5 ± 0.6) × 10 ²¹ cm^-2, photon index Γ = 1.6 ± 0.1, and luminosity L _{0.5-8 keV} 1.3 × 10³³ d ² ₃ erg s^-1, where d ₃ is the distance scaled to 3 kpc. This emission likely includes an unresolved part of the pulsar wind nebula (PWN) created by the colliding winds from the pulsar and the Be companion, and a contribution from the pulsar magnetosphere. The extended emission apparently consists of two components. The highly significant compact component looks like a southward extension of the point-like source image, seen up to 4″ from the pulsar position. Its spectrum has about the same slope as the point-like source spectrum, while its luminosity is a factor of 10 lower. We also detected an elongated feature extended ∼15″ southwest of the pulsar, but the significance of this detection is marginal. We tentatively interpret the resolved compact PWN component as a shocked pulsar wind blown out of the binary by the wind of the Be component, while the elongated component could be a pulsar jet.