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We report on a sequence of Chandra X-ray Observatory observations of the TWHydrae brown dwarf (BD) 2MASSW J1139511-315921 (2M1139). In the combined 31 ksACIS-S exposure, 2M1139 is detected at the 3-sigma confidence level. We find anX-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 +/- 0.3. This object is similar to another TW Hydrae BD member, CD-337795B (TWA 5B): both have H-alpha emission, both show no signatures ofaccretion, and both have comparable ages and spectral types. TWA 5B waspreviously detected in X-rays with a luminosity of L_X = 4 x 10^27 ergs s^-1 orlog(L_X/L_bol) = -3.4, an order of magnitude more luminous in X-rays than2M1139. We find that the discrepancy between the X-ray luminosity of 2M1139 andTWA 5B is consistent with the spread in X-ray luminosity in the Orion NebulaCluster (ONC) for BDs of similar spectral types. Though rotation may play arole in the X-ray activity of ultracool dwarfs like 2M1139 and TWA 5B, thediscrepancy cannot be explained by rotation alone. We also examine two X-raybright objects in the FOV of our Chandra observations and find one to be ofspectral 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 phaseof an X-ray flare.

A Chandra Observation of the TW Hydrae Association Brown Dwarf 2MASSW J1139511-315921