We report on a sequence of Chandra X-ray Observatory observations of the TW Hydrae brown dwarf ( BD ) 2MASSW J1139511-315921 ( 2M1139 ) .
In the combined 31 ks ACIS-S exposure , 2M1139 is detected at the 3 \sigma confidence level .
We find an X-ray luminosity of L _ { X } = 1.4 ^ { +2.7 } _ { -1.0 } x 10 ^ { 26 } ergs s ^ { -1 } or \log L _ { X } / L _ { bol } = -4.8 \pm 0.3 .
This object is similar to another TW Hydrae BD member , CD-33 7795B ( TWA 5B ) : both have H \alpha emission , both show no signatures of accretion , and both have comparable ages and spectral types .
TWA 5B was previously detected in X-rays with a luminosity of L _ { X } = 4 x 10 ^ { 27 } ergs s ^ { -1 } or \log L _ { X } / L _ { bol } = -3.4 , an order of magnitude more luminous in X-rays than 2M1139 .
We find that the discrepancy between the X-ray luminosity of 2M1139 and TWA 5B is consistent with the spread in X-ray luminosity in the Orion Nebula Cluster ( ONC ) for BDs of similar spectral types .
Though rotation may play a role in the X-ray activity of ultracool dwarfs like 2M1139 and TWA 5B , the discrepancy can not be explained by rotation alone .
We also examine two X-ray bright objects in the FOV of our Chandra observations and find one to be of spectral type K0IV and identify it as a possible RS Canum Venaticorum ( RS CVn ) , and another X-ray bright object whose light-curve clearly shows the decay phase of an X-ray flare .