X-ray detections of two young bona-fide brown dwarfs

Abstract

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 LX = 8.35 ± 2.86 × 1028 erg s-1 and L= 6.54 ± 1.35 × 1028 erg s -1 respectively, corresponding to luminosity ratios of log(L X/Lbol) = -2.07 and log(LX/Lbol) = -2.69. The two sources were close to the limit of detection of the instruments at only 2∼3σ 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. (2001) with a luminosity ∼14 times fainter than the one reported here, indicating that the X-ray emission of this object is strongly variable.