Abstract
We present a systematic study of the recently reported anticorrelation between X-ray flux and photon index (Gamma) in the Crab Nebula, using archival Rossi X-Ray Timing Explorer (RXTE) Proportional Counter Array (3-50 keV), RXTE High Energy X-ray Timing Experiment (HEXTE; 20-100 keV), and Nuclear Spectroscopic Telescope Array (3-78 keV) observations. Spectra were extracted in soft (3-10 keV) and hard bands (10-50, 10-78, 20-100 keV) and fitted with an absorbed power-law model. Across all instruments and energy ranges, we confirm the existence of a persistent negative correlation-harder spectra at higher flux levels. The correlation is stronger in the hard bands compared to the soft bands. This is consistent with synchrotron emission modulated by magnetic-field variations in the pulsar wind nebula.