Detection of X-ray emission from gravitationally lensed submillimeter sources in the field of Abell 370

We report the detection by Chandra of SMM J02399 - 0134 and SMM J02399 - 0136, two distant (z = 1.06 and z = 2.81, respectively) submillimeter sources gravitationally magnified by the galaxy cluster Abell 370. These are high-significance (>7 σ) X-ray detections of the high-redshift submillimeter source population. The X-ray positions are coincident with the optical positions to within 1″. The X-ray spectra, while of low signal-to-noise ratio, are quite hard. Absorbed power-law models with fixed photon indices of Γ = 2.0 imply local absorbing columns greater than 2 × 10²³ cm^-2 and unabsorbed luminosities greater than 10⁴⁴ ergs s^-1 in both sources. These results imply that nuclear activity is responsible for the bulk of the luminosity in SMM J02399-0134 and for at least 20% of the luminosity of SMM J02399-0136, consistent with previous optical observations. We also place an upper limit on the X-ray flux of a third submillimeter source, SMM J02400-0134. Considered together with previously published Chandra upper limits on the X-ray flux from submillimeter sources, our results imply that 20⁺³⁰_-16% of submillimeter sources exhibit X-ray emission from active galactic nuclei (with 90% confidence), consistent with expectations of their contribution to the diffuse X-ray background.