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 × 10 28 erg s −1 and LX = 6.54 ± 1.35 × 10 28 erg s −1 respectively, corresponding to luminosity ratios of log (LX/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∼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. (2001) with a luminosity ∼14 times fainter than the one reported here, indicating that the X-ray emission of this object is strongly variable.