The X-ray emission from Z Canis Majoris during an FUor-like outburst and the detection of its X-ray jet

¹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: stelzer@astropa.unipa.it
² European Southern Observatory, Casilla 19001, Santiago 19, Chile
³ Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlarska 2, 61137 Brno, Czech Republic
⁴ Observatory and Planetarium of Johann Palisa, VŠB–TU Ostrava, Czech Republic
⁵ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

Received: 29 January 2009
Accepted: 16 March 2009

Abstract

Accretion shocks have been recognized as an important X-ray emission mechanism for pre-main sequence stars, and yet the X-ray properties of FUor outbursts, events that are caused by violent accretion, have been given little attention. We observed the FUor object Z CMa during optical outburst and quiescence with Chandra. No significant changes in X-ray brightness and spectral shape were found, suggesting that the X-ray emission is coronal. The binary nature of Z CMa makes the origin of the X-ray source ambiguous. However, the moderate hydrogen column density derived from our data makes it unlikely that the embedded primary star is the X-ray source. The secondary star, which is the FUor object, is thus responsible for both the X-ray emission and the ongoing accretion outburst, which seem, however, to be unrelated phenomena. The secondary is also known to drive a large outflow and jet, which we detect here for the first time in X-rays. The distance of the X-ray emitting outflow source to the central star is greater than in jets of low-mass stars.