The X-Ray spectrum of the Vela pulsar resolved with the Chandra X-Ray Observatory

G. G. Pavlov, V. E. Zavlin, D. Sanwal, V. Burwitz, G. P. Garmire

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Abstract

We report the results of the spectral analysis of two observations of the Vela pulsar with the Chandra X-Ray Observatory. The spectrum of the pulsar does not show statistically significant spectral lines in the observed 0.25-8.0 keV band. Similar to middle-aged pulsars with detected thermal emission, the spectrum consists of two distinct components. The softer component can be modeled as a magnetic hydrogen atmosphere spectrum - for the pulsar magnetic field B = 3 × 1012 G and neutron star mass M = 1.4 M and radius R = 13 km, we obtain Teff = 0.68 ± 0.03 MK, Lbol = (2.6 ± 0.2) × 1032 ergs s-1, and d = 210 ± 20 pc (the effective temperature, bolometric luminosity, and radius are as measured by a distant observer). The effective temperature is lower than that predicted by standard neutron star cooling models. A standard blackbody fit gives T = 1.49 ± 0.04 MK, Lbol = (1.5 ± 0.4) × 1032d2250 ergs s-1 (d250 is the distance in units of 250 pc); the blackbody temperature corresponds to a radius R = (2.1 ± 0.2)d250 km, much smaller than realistic neutron star radii. The harder component can be modeled as a power-law spectrum, with parameters depending on the model adopted for the soft component: γ = 1.5 ± 0.3, Lx = (1.5 ± 0.4) × 1031d2250 ergs s-1 and γ = 2.7 ± 0.4, Lx = (4.2 ± 0.6) × 1031d2250 ergs s-1 for the hydrogen atmosphere and blackbody soft component, respectively (γ is the photon index; Lx is the luminosity in the 0.2-8 keV band). The extrapolation of the power-law component of the former fit toward lower energies matches the optical flux at γ ≃ 1.35-1.45.

Original languageEnglish (US)
Pages (from-to)L129-L133
JournalAstrophysical Journal
Volume552
Issue number2 PART 2
DOIs
StatePublished - May 10 2001

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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