VLF ionosonde and long-distance propagation anomalies produced by galactic Cen X-4 X-ray burst in May 1979

The galactic X-ray source Cen X-4 produced a large outburst in May 1979, measured by the Ariel-5 satellite. Low ionosphere group heights measured daily by a VLF ionosonde indicated an anomalous lowering of the effective reflection height in good correlation with the Cen X-4 burst as well as an increase in the reflection coefficient, larger for larger frequencies. Diurnal VLF phase variations in a long-distance propagation path presented night-time 3-4σ deviations from the average in some days during the Cen X-4 bursting period. The geomagnetic activity in the period covered by this investigation was low, and the results obtained are a suggested confirmation that galactic transient X-ray sources are capable of producing sufficient ionization effects to be detected as low ionosphere anomalies. (author)