Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...429..832y&link_type=abstract
The Astrophysical Journal, vol. 429, no. 2, pt. 1, p. 832-843
Astronomy and Astrophysics
Astrophysics
67
Astronomical Models, Magnetic Poles, Neutron Stars, Polar Caps, Pulsars, Pulsed Radiation, Stellar Mass Accretion, Surface Temperature, X Ray Imagery, X Ray Spectra, X Rays, Background Noise, Luminosity, Position Sensing, Proportional Counters, Rosat Mission, Subtraction, Temperature Dependence
Scientific paper
As part of a search for thermal surface radiation from nearby neutron stars, we have carried out a 45,000 s observation of the nearby radio pulsar PSR 1929+10 with the ROSAT PSPC. After background subtraction, a net of 420 +/- 25 photons in the 0.1 to 2.0 keV band were detected at the position of the pulsar, corresponding to a luminosity of 1.2 x 1030 ergs/sec for a source distance of 250 pc, or approximately 3 x 10-4 of the pulsar's spin-down luminosity. We find coherent pulsations from PSR 1929+10 at the radio period of 0.2265 s. The folded light curve is well fitted by a sinusoidal oscillation with a pulsed fraction of about 30%. The total spectrum is fitted by a blackbody with a temperature Tinfinity approximately equals 3.2 x 106 K; the implied emitting area has a radius of less than 50 m. The maximum of the X-ray light curve coincides with the radio pulse, suggesting that we are detecting the hot magnetic polar cap of the star. The temperature limit for the remainder of the stellar surface is Tinfinity less than 3 x 105 K. The spatial distribution of the photons is consistent with the instrument point-spread function. We discuss the implications of these results for the temperature distribution over the surface of the star and use this detection to constrain various heating mechanisms for rotation-powered neutron stars. We also use a simple model of general relativistic light bending near the stellar surface in conjunction with the radio emission geometry and the X-ray pulsed fraction to derive a radius for the neutron star of R = 9 +/- 3 km.
Hamilton Thomas T.
Helfand David J.
Yancopoulos S.
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