2004A&A...424..619B

I report the detection of two bona-fide brown dwarfs by XMM-Newton: [GY92] 141 in the ρ-Ophiuchus star-forming region and DENIS J155601-233809 in the Upper Scorpius OB association. The two objects have been detected with luminosities of L_X=8.35±2.86x10²⁸erg/s and L_X=6.54±1.35x10²⁸erg/s respectively, corresponding to luminosity ratios of log(L_X/L_bol)=-2.07 and log(L_X/L_bol)=-2.69. The two sources were close to the limit of detection of the instruments at only 2∼3-σ above the background level, and no significant flare or variation could be detected during the 48.3 ks and 33.9 ks observations. [GY92] 141 had already been observed 10 months earlier with Chandra by Imanishi et al. (2001ApJ...563..361I) with a luminosity ∼14 times fainter than the one reported here, indicating that the X-ray emission of this object is strongly variable.