BVRI observations of PSR B0656+14 with the 6-meter telescope

Abstract

We observed the middle-aged radio pulsar 0656+14 with a CCD detector at the 6-m telescope. Broadband BVRI images show the following magnitudes of the pulsar counterpart: B = 24.85 (+0.19, -0.16), V = 24.90 (+0.16, -0.14), R = 24.52 (+0.12, -0.11), I = 23.81 (+0.27, -0.21). We fitted the UV-optical (space + ground-based) data with a two-component model which combines a power law (non-thermal component) with a thermal spectrum emitted by the neutron star surface. The power law component, with the energy power-law index α=1.5 (+1.1,-1.2), dominates in the observed range. Constraints on the thermal component correspond to the Rayleigh-Jeans parameter G\equiv T_6(R_{10}/d_{500})^2=4.1 (+2.1, -4.1), where $T=10^6T_6$ K is the brightness temperature, R_\infty = 10 R_{10}$ km is the neutron star radius as seen by a distant observer, and $d=500 d_{500}$ pc is the distance. The shape of the optical-UV spectrum of PSR 0656+14 differs considerably from those observed from other pulsars: the middle-aged Geminga and young Crab, Vela.