On the complex X-ray structure tracing the motion of Geminga

A deep (100 ks) XMM-Newton observation of Geminga has shown two faint tails of diffuse X-ray emission, extending for similar to 2' behind the pulsar, well aligned with the proper motion ( PM) direction. We report here on a recent similar to 20 ks Chandra observation, which unveils a new structure, similar to 25 long and similar to 5 thick, starting at the pulsar position and perfectly aligned with the PM direction, with a surface brightness similar to 40 times higher than that of the XMM Tails. The Chandra comet-like feature has a remarkably hard spectrum (photon index similar to 0.9-1.4) and a luminosity of similar to 5.5 x 10(28) erg s(-1), comparable to the energetics of the larger XMM one. Geminga is thus the first neutron star to show a clear X-ray evidence, of a large-scale, outer bow-shock as well as a short, inner cometary trail.