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The discovery of 8.7 S pulsations from the ultrasoft X-ray source 4U0142+61

Mereghetti, S.; Stella, L.; Israel, G. L.

We discovered a periodicity at ~8.7 s from the X-ray sources 4U0142+61, previously considered a possible black hole candidate on the basis of its ultrasoft spectrum. The pulsations are visible only in the 1-4 keV energy range, during an observation obtained with the EXOSAT satellite in August 1984. In the same data, periodic oscillations at 25 min…