Discovery of X-ray emission from the eclipsing brown-dwarf binary 2MASS J05352184-0546085.pdfVIP

a r X i v : 0 8 0 9 .4 1 2 9 v 1 [ a s t r o - p h ] 2 4 S e p 2 0 0 8 Astronomy Astrophysics manuscript no. 0818text c? ESO 2008 September 24, 2008 Discovery of X-ray emission from the eclipsing brown-dwarf binary 2MASS 0546085 S. Czesla, P. C. Schneider, and J. H. M. M. Schmitt Hamburger Sternwarte, Universita?t Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany Received ... / accepted ... ABSTRACT The eclipsing brown-dwarf binary system 2MASS 0546085 is a case sui generis. For the first time, it allows a detailed analysis of the individual properties of young brown dwarfs, in particular, masses, and radii, and the temperature ratio of the system components can be determined accurately. The system shows a “temperature reversal” with the more massive component being the cooler one, and both components are found to be active. We analyze X-ray images obtained by Chandra and XMM-Newton containing 2MASS 0546085 in their respective field of view. The Chandra observatory data show a clear X-ray source at the position of 2MASS 0546085, whereas the XMM-Newton data suffer from contamination from other nearby sources, but are consistent with the Chandra detection. No indications of flaring activity are found in either of the observations (together ≈ 70 ks), and we thus attribute the observed flux to quiescent emission. With an X-ray luminosity of 3 × 1028 erg/s we find an LX/Lbol-ratio close to the saturation limit of 10 ?3 and an LX/LHα-ratio consistent with values obtained from low-mass stars. The X-ray detection of 2MASS 0546085 reported here provides additional support for the interpretation of the temperature reversal in terms of magnetically suppressed convection, and suggests that the activity phenomena of young brown dwarfs resemble those of their more massive counterparts. Key words. Stars: low-mass, brown dwarfs — (Stars:) binaries: eclipsing — Stars: activity — X-rays: individuals: 2MASS 0546085