We report the results of the first X–ray observation of the luminous and helium–rich O–type subdwarf BD +37 ^ { \circ } 442 carried out with the XMM–Newton satellite in August 2011 .
X–ray emission is detected with a flux of about 3 \times 10 ^ { -14 } erg cm ^ { -2 } s ^ { -1 } ( 0.2–1 keV ) and a very soft spectrum , well fit by the sum of a blackbody with temperature kT _ { BB } = 45 ^ { +11 } _ { -9 } eV , and a power law with a poorly constrained photon index .
Significant pulsations with a period of 19.2 s are detected , indicating that the X–ray emission originates in a white dwarf or neutron star companion , most likely powered by accretion from the wind of BD +37 ^ { \circ } 442 .