AAS 200th meeting, Albuquerque, NM, June 2002
Session 80. Neutron Stars, Relativity, MHO
Oral, Thursday, June 6, 2002, 10:00-11:30am, San Miguel

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[80.01] Detection of Photospheric Absorption Features and the Gravitational Redshift at the Surface of a Neutron Star

G. G. Pavlov, D. Sanwal, M. A. Teter (Penn State), V. E. Zavlin (MPE, Garching)

We observed 1E 1207.4--5209, a radio-quiet neutron star (NS) at the center of the supernova remnant PKS 1209--51/52, with the Chandra ACIS detector and found absorption features in its thermal-like spectrum, centered at 0.74 keV and 1.42 keV. This first firm detection of absorption features in the spectrum of an isolated neutron star allows one to measure the gravitational redshift at the NS surface (hence, the NS mass-to-radius ratio) once the features are properly identified. We suggest that the features can be interpreted as absorption lines of once-ionized helium in a strong magnetic field. This interpretation yields the magnetic field strength of 140--170 Teragauss and the gravitational redshift z=0.12--0.23, which corresponds to R/M=8.8--14.2 km~M\odot-1. Our model predicts that deep observations with higher spectral resolution can detect additional absorption lines from both ionized and neutral helium, which would confirm our interpretation and yield much more accurate values of the gravitational redshift.

The work was supported by SAO grant GO2-3088X and NASA grant NAG5-10865.

The author(s) of this abstract have provided an email address for comments about the abstract: pavlov@astro.psu.edu

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.