Mass and Radius of Neutron Stars from Modeling Pulse Shapes of Millisecond Pulsars
Denis Leahy
University of Calgary
Millisecond pulsars are rapidly rotating neutron stars where general
relativity plays a strong role in the propagation of light from the
neutron star to observer and formation of observed pules shapes. Thus
pulse shapes carry information on the mass, radius and surface shape
of the neutron star. Comparison of calculations of pulse shapes with
observed pulse shapes can give useful constraints on mass and radius, which
constrain the equation of state (EOS) of matter at high density. Here,
calculations are described for the modeling of X-ray pulse shapes. These
include General Relativity for the neutron star metric and for geodesics
for photons in that metric; time-delays and Doppler effects for photons;
and oblateness of the neutron star surface, which results from the
rapid rotation. Frame dragging is also calculated bit shown to be not
important for observed rotation periods. The modeling has been applied to
Rossi X-Ray Timing Explorer observations of the millisecond pulsars XTE
J1814-334 and SAX J1808-3658. The most recent results include modeling
multi-epoch pulse shapes from the 1998, 2002 and 2005 outbursts of SAX
J1808-3658. It is a challenging test for the model to fit these greatly
different pulse shapes. A consistent neutron star model can work only if
the model includes an extra component: light scattered from the accretion
disk. The new mass and radius constraints are for SAX J1808-3658 are
presented and compared to those for other neutron stars.
Date: | Mercredi, le 10 novembre 2010 |
Heure: | 14:00 |
Lieu: | Université McGill |
| Ernest Rutherford Physics Building, room 326 |
Contact: | Robert Rutledge |
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