Mathematics – Logic
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........4m&link_type=abstract
Thesis (PhD). UNIVERSITY OF CALIFORNIA, SAN DIEGO, Source DAI-B 60/06, p. 2748, Dec 1999, 310 pages.
Mathematics
Logic
1
Magnetar, Wind Spindown, Quantum Critical Field
Scientific paper
Soft gamma-ray repeaters (SGRs) are a class of astrophysical sources that emit bursts of high energy x- ray and gamma-ray radiation which are among the most energetic events in the Galaxy. Their coherent pulsations, energetics, and associations with supernova remnants suggest that they are young neutron stars, yet the mechanism powering their burst and quiescent x-ray emission is not known. The most popular model for SGRs is the magnetar model, in which SGR are endowed with surface magnetic fields of greater than 1014 G, which would make the SGR magnetic fields ~ 10-100 times more powerful than those of canonical neutron stars. If SGRs are magnetars, then they have magnetic fields much greater than the quantum critical field (Bq ~ 4.4 × 1013 G), making them unique laboratories for the study of quantum processes such as vacuum polarization and photon splitting. This thesis uses observational data at x-ray wavelengths to study the temporal, spectral, and morphological characteristics of SGRs 0526-66, 1806-20, and 1900+14. I find that many of the popularly held views concerning SGRs are not supported by the new data, and I also find some features of the temporal and spectral behavior of SGR bursts which had not been seen previously. In particular, I find that the temporal behavior of the SGR 1900+14 does not support the interpretation that this source is a magnetar, and instead the spindown behavior is consistent with the emission of a relativistic wind. The physics of the wind spindown of SGRs is explored briefly, and I find that the observed spindown rate of SGR 1900+14 can be produced by the continuous excitation of small amplitude Alfvén waves in the magnetosphere of the neutron star. The required magnetic field strength for this mechanism is consistent with the fields of normal ( ~ 1012 G) neutron stars, and therefore does not require a magnetar. The excitation mechanism of the wind is not known, however, and more theoretical work is needed on the physical mechanism responsible for the wind. More temporal observations of the SGRs are also needed to determine the long-term spindown behavior of these fascinating objects.
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