I report here the detection of two bona-fide brown dwarfs by XMM-Newton : [ GY92 ] ~141 in the \rho -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 \pm 2.86 \times 10 ^ { 28 } Â erg s ^ { -1 } and L _ { X } =6.54 \pm 1.35 \times 10 ^ { 28 } Â erg s ^ { -1 } 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 \sim 3- \sigma above the background level , and no significant flare or variation could be detected during the 48.3Â ks and 33.9Â ks observations .
[ GY92 ] Â 141 had already been observed 10 months earlier with Chandra by ( ) with a luminosity \sim 14 times fainter than the one I report here , meaning that the X-ray emission of this object is strongly variable .