Multiwavelength spectral observations of middle-aged (τ ∼ 104-106 yr) isolated pulsars enable one in principle to separate thermal radiation emitted from the neutron star surface and nonthermal radiation from its magnetosphere. We have previously detected the middle-aged radio and soft X-ray pulsar 0656+14 with the Hubble Space Telescope Faint Object Camera (FOC) long-pass filter F130LP. In the present Letter we report new FOC observations of this pulsar with three broadband filters: F430W, F342W, and F195W. The optical-UV spectral flux can be fitted with a two-component spectral model that combines a power-law spectrum with a Rayleigh-Jeans spectrum. The nonthermal component with the power-law index α = 1.4+0.6-0.7 dominates at λ ≳ 3000 Å. The thermal component is characterized by the Rayleigh-Jeans parameter, G ≡ T6(R10/d500)2, where T = 106T6 K is the brightness temperature, R∞ = 10R10 km is the neutron star radius as seen by a distant observer, and d = 500d500 pc is the distance. For a plausible extinction, E(B - V) = 0.03, we obtained G = 3.6-2.0+1.6. The observed shape of the optical-UV spectrum of PSR 0656+14 differs drastically from those of both younger pulsars (Crab, 0540-69, Vela) and the older pulsar Geminga.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science