Measuring surface temperature of isolated neutron stars and related problems
Abstract
New and exciting results for measuring neutron star surface temperatures began with the successful launch of the Chandra X-ray observatory. Among these results are new detections of neutron star surface temperatures which have made it possible to seriously test neutron star thermal evolution theories. The important new temperature determination of the Vela pulsar (Pavlov, et al., 2001a) requires a non-standard cooling scenario to explain it.
Apart from this result, we have measured PSR B1055-52's surface temperature in this thesis, determining that it can be explained by standard cooling with heating. Our spectral fit of the combined data from ROSAT and Chandra have shown that a three component model, two thermal blackbodies and an non-thermal power-law, is required to explain the data. Furthermore, our phase resolved spectroscopy has begun to shed light on the geometry of the hot spot on PSR B1055-52's surface as well as the structure of the magnetospheric radiation. Also, there is strong evidence for a thermal distribution over its surface. Most importantly, the fact that PSR B1055-52 does not have a hydrogen atmosphere has been firmly established. To reconcile these two key observations, on the Vela pulsar and PSR B1055-52, we tested neutron star cooling with neutrino processes including the Cooper pair neutrino emission process. Overall, it has been found that a phase change associated with pions being present in the cores of more massive neutron stars explains all current of the data. A transition from neutron matter to pion condensates in the central stellar core explains the difference between standard and non-standard cooling scenarios, because the superfluid suppression of pion cooling will reduce the emissivity of the pion direct URCA process substantially. A neutron star with a mass of [Special characters omitted.] with a medium stiffness equation of state and a T72 type neutron superfluid models the standard cooling case well. A neutron star of [Special characters omitted.] , with a pion core, with the same type of equation of state modified for pion matter and a modified E1-0.6 pion superfluid model is the best option for the non-standard case. The results also suggest that the equation of state for neutron stars may have to be stiffer than medium. Furthermore, our observational results from two other sources, SGR 1900+14 and 1E1207.4-5209, have helped us to expand the understanding of isolated neutron stars. The Chandra observation of SGR 1900+14 has strengthened the case that it is a magnetar, as the pulsed fraction and the spectral fits suggest a blackbody plus power-law model is preferred. Also, our analysis of the Chandra data of 1E1207.4-5209 suggests that it should have a hydrogen atmosphere. Future observations will certainly give even better insight to both of these objects, as well as PSR B1055-52.- Publication:
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Ph.D. Thesis
- Pub Date:
- 2001
- Bibcode:
- 2001PhDT........57T
- Keywords:
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- Chandra;
- X-Ray