Extended X-ray emission from the classic nova DQ Her - on the possible presence of a magnetized jet

We present an analysis of archival Chandra and XMM-Newton observations of the magnetically active cataclysmic variable DQ Her and the shell around it ejected in a nova event in 1934. A careful revision of the Chandra observations confirms previous claims on the presence of extended X-ray emission around DQ Her and reveals that it actually corresponds to a bipolar jet-like structure extending ≃32 arcsec along a direction from north-east to south-west. Therefore, this X-ray emission extends beyond the optical nova shell and is perpendicular to its major axis. The XMM-Newton observations confirm the presence of the extended X-ray emission detected by Chandra, suggesting the additional presence of a diffuse X-ray emission from a hot bubble filling the nova shell. This hot bubble was very likely produced by the explosion that created the nebular shell detected in optical images. The bipolar feature can be modelled by the combination of an optically thin plasma emission component with temperature T ≈ 2 × 10⁶ K and a power-law component with a photon index of Γ = 1.1 ± 0.9. Its X-ray luminosity in the 0.3-5 keV energy range is L_X = (2.1 ± 1.3) × 10²⁹ erg s^-1, for an electron density n_e ≈ 2 cm^-3 and a mass m_X ≈ 3 × 10^-6 M_⊙. We suggest that the X-ray bipolar structure in DQ Her is a jet and interpret its non-thermal X-ray emission in terms of a magnetized jet.