Letter to the Editor

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

¹ INAF – IASF, Via Bassini 15, 20133 Milano, Italy e-mail: deluca@iasf-milano.inaf.it
² Università di Milano Bicocca, Dipartimento di Fisica, P.za della Scienza 3, 20126 Milano, Italy
³ CESR/CNRS, 9 Av. du colonel Roche, 31028 Toulouse Cedex 4, France
⁴ Università degli Studi di Pavia, Dipartimento di Fisica Nucleare e Teorica, via Bassi 4, 27100 Pavia, Italy

Received: 17 August 2005
Accepted: 13 November 2005

Abstract

A deep (100 ks) XMM-Newton observation of Geminga has shown two faint tails of diffuse X-ray emission, extending for ~ behind the pulsar, well aligned with the proper motion (PM) direction. We report here on a recent ~20 ks Chandra observation, which unveils a new structure, ~ long and ~ 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 ~) and a luminosity of ~ 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.