Abstract
THE γ-ray source CG195+4 (Geminga) discovered by SAS 2 and further observed by COS B has a period of 59 s which is increasing at a rate Ṗ = 2×10−9 (refs 1,2). If the periodicity is produced by a neutron star which is spinning down at the observed rate, then the rate at which rotational energy is being lost is L ∼ 3×1032 erg s−1 (ref. 3). The observed γ-ray flux of 3×10−6 photon cm−2 s−1 with energy E>100 MeV implies that the distance, d, to the source is given by d ≃ 73f1/2 pc where f(≳ 1) is the fraction of the total energy output which is emitted as γ-rays. Theoretical studies of the evolution of binary systems which give rise to the binary X-ray sources have led to the suggestion that, before the neutron star starts to accrete and spin up (that is, before the X-ray source turns on) it spends a comparatively long time being spun down in the weak stellar wind of its companion4. This leads us to seek a candidate companion for the γ-ray source which is an early type star at a distance of ≳ 70 pc. As we report here, the only object which satisfies these constraints is γ Geminorum.
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DAVIES, R., FABIAN, A. & PRINGLE, J. γ-Rays from γ Geminorum?. Nature 271, 634–635 (1978). https://doi.org/10.1038/271634a0
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DOI: https://doi.org/10.1038/271634a0
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