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

摘要: Abstract We discovered a periodicity at ∼8.7 s from the X-ray sources 4U142+61, previously considered possible black hole candidate on basis of its ultrasoft spectrum. The pulsations are visible only in 1–4 keV energy range, during an observation obtained with EXOSAT satellite August 1984. In same data, periodic oscillations 25 minutes had been found additional hard spectral component dominating above 4 keV. A search for delays pulse arrival times caused by orbital motion gave negative results. Though very high (>10 ) to optical flux ratio 4U0142+61 is compatible models based isolated neutron star, simplest explanation involves low mass binary faint companion, similar 4U1626-67. discovery weakens phenomenological criterion that signature accreting holes.