A hard X-ray observation 8400 s long of the recurrent transient X-ray pulsar A0535 + 26 has been performed. The data were obtained with a balloon-borne experiment in the energy range 27-190 keV when the source was near the maximum of the 1980 October transient outburst. Results from the pulse shape analysis show that the time-averaged pulse profile in the hard X-ray range is quite different from that measured by other observers at different epochs. It exhibits a double-peaked structure fairly stable with energy, with the greatest variation seen in the intensity ratio between the two peaks. In addition, the pulsed fraction shows a clear increase at higher energies, which converges to 100 percent at about 100 keV. A timing analysis has shown significant pulse period variations (up to an absolute value of Delta P/P of about 0.007) on time scales of thousands of seconds. Finally, a high variability in pulse shape and intensity was discovered on time scales varying from the order of seconds to few tens of minutes. The short time scale variability was studied using Power Spectral Density estimates and direct inspection of the data. This variability appears to be chaotic, and shot-like events with typical duration of 10 s and mean frequency of one every 25 s have been observed. --------------------------------------------------------------------------------
The X-ray Pulsar A0535+26: Pulse profile and its Time variability in Hard X-rays
FRONTERA, Filippo;
1985
Abstract
A hard X-ray observation 8400 s long of the recurrent transient X-ray pulsar A0535 + 26 has been performed. The data were obtained with a balloon-borne experiment in the energy range 27-190 keV when the source was near the maximum of the 1980 October transient outburst. Results from the pulse shape analysis show that the time-averaged pulse profile in the hard X-ray range is quite different from that measured by other observers at different epochs. It exhibits a double-peaked structure fairly stable with energy, with the greatest variation seen in the intensity ratio between the two peaks. In addition, the pulsed fraction shows a clear increase at higher energies, which converges to 100 percent at about 100 keV. A timing analysis has shown significant pulse period variations (up to an absolute value of Delta P/P of about 0.007) on time scales of thousands of seconds. Finally, a high variability in pulse shape and intensity was discovered on time scales varying from the order of seconds to few tens of minutes. The short time scale variability was studied using Power Spectral Density estimates and direct inspection of the data. This variability appears to be chaotic, and shot-like events with typical duration of 10 s and mean frequency of one every 25 s have been observed. --------------------------------------------------------------------------------I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
