A Study of Temporal-Spectral Behavior of Hercules X-1: a Binary X-Ray Pulsar.
Abstract
The 12-180 keV temporal and spectral variations of the rotating, highly magnetized neutron star, Hercules X-1, in the accreting close binary stellar system, are the subjects of this dissertation. Analysis of these variations with respect to different time scales and energy ranges provides for a semi-quantitative understanding of the accretion, emission, and beam formation mechanisms in a physical setting unobtainable in the laboratory. The seventeen month lifetime of HEAO-1 provided for the study of the temporal-spectral behavior of bright astronomical X-ray sources with large area scintillation detectors in the energy range 12 keV to 10 MeV. Hercules X-1 is one of the brightest binary X-ray pulsars and exhibits a 1.24s neutron star rotation period, a 1.7d binary period, a 35d on-off cycle, of which the underlying mechanism is as yet unclear, and its X-ray spectrum reveals a 30-50 keV feature. If a cyclotron line of transition between quantized electronic Landau levels is responsible, a 3-5 times 1012 Gauss surface magnetic field is then implied. The results of this dissertation contain pulse profile changes with intensity and 35d phase, as well as variations in main-on states (a high X-ray intensity state of ~11^{d } duration within the 35^{d } on-off cycle) that rule out the precession of neutron star as the direct cause of the X-ray intensity and beaming pattern modulation. The conclusion is that the angle between the magnetic axis and the inner disk plane changes with the 35d period, and, since the channelling of accreting matter to the emission region is dependent on this angle, the beaming geometry varies throughout the 35^ {d} cycle. Optically thick matter at the inner disk region and extending above the disk plane along the magnetic field lines modulates the observed X -ray emission by a differential blockage. The main pulse is beamed along the magnetic axis, and its structure represents a "funnel" geometry, with both magnetic poles contributing to the overall emission. Some of the conclusions are by no means decisive; however, I have suggested some future observations that may resolve the current issues. I urge theorists to study the related dynamics as well.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1988
- Bibcode:
- 1988PhDT.........4S
- Keywords:
-
- Physics: Astronomy and Astrophysics;
- Pulsars;
- Spectral Emission;
- Stellar Mass Accretion;
- X Ray Binaries;
- X Ray Stars;
- Beams (Radiation);
- Emission Spectra;
- Magnetic Fields;
- Spectrum Analysis;
- X Ray Spectra;
- Astrophysics