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 L_X =8.35 ± 2.86 × 10²⁸ erg s^-1 and L_X =6.54 ± 1.35 × 10 ²⁸ 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∼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 \citet{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.

Based on observations obtained with the ESA XMM-Newton Satellite, reported in the The First XMM-Newton Serendipitous Source Catalogue, XMM-Newton Survey Science Centre (SSC), 2003.