Daily observations of the binary X-ray pulsar GX 1+4 were made with the Rossi X-ray Timing Explorer ( RXTE ) satellite between 1997 May 16–20 as part of a four-month monitoring program .
On May 17 the sharp dips normally observed in the lightcurve were all but absent , resulting in a pulse fraction f _ { p } \approx 0.5 instead of the more typical value of \approx 0.8 measured before and after .
Also observed was a dramatic hardening of the 2–40 keV phase-averaged spectrum .
The power-law photon index was 1.16 \pm 0.02 , whereas values of 1.6–2.0 are more typical .
In terms of a Comptonization continuum component , the optical depth for scattering was \tau \approx 19 , with 4–6 the usual range for RXTE spectra ( 9 ) .
Pulse-phase spectrosopy indicates that \tau is decreased relative to the phase-averaged value around the primary minimum , where an increase is normally observed .
The reduced depth of the dip is interpreted as disruption of the accretion column , and the accompanying spectral variation suggests a substantially different accretion regime than is usual for this source .