Long-Term Monitoring of the Accreting Pulsar GX 1+4

We present preliminary results from two years of GRO/BATSE hard X‐ray (20–100 keV) monitoring of the ∼120 s accretion‐powered pulsar GX 1+4. Daily pulse frequency measurements from 1991 April to 1993 September show an average spin‐down of ḟ≊−5×10^(−12) s^(−2), with increases in the spin‐down rate during high‐luminosity intervals. The 20–100 keV pulsed flux spectrum for the interval TJD 8393–8406 is fit by a power‐law index of 2.56±0.04. Optical spectroscopy of the suggested red giant companion V2116 Oph taken during the 1993 September X‐ray outburst from GX 1+4 show considerably strengthened emission line features, supporting the association