2006A&A...445L...9D

A deep (100ks) XMM-Newton observation of Geminga has shown two faint tails of diffuse X-ray emission, extending for ∼2' behind the pulsar, well aligned with the proper motion (PM) direction. We report here on a recent ∼20ks Chandra observation, which unveils a new structure, ∼25'' long and ∼5'' thick, starting at the pulsar position and perfectly aligned with the PM direction, with a surface brightness ∼40 times higher than that of the XMM Tails. The Chandra comet-like feature has a remarkably hard spectrum (photon index ∼0.9-1.4) and a luminosity of ∼5.5x10²⁸erg/s, 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.