The formation of helium lines in the spectrum of COM J1740-5340

Abstract

The He I 5876A absorption line recently discovered in the spectrum of the companion to the millisecond pulsar PSR J1740-5340 is tentatively attributed to electron impact excitations due to the irradiation of its atmosphere by gamma-rays emitted by the pulsar's magnetosphere. Numerical calculations, similar to those carried out previously for Type Ib SNe, indicate that a pulsar beam with photon energies ~ 1 MeV gives rise to a 5876A line of the observed strength if the beam's spin-down conversion efficiency approaches 1%. However, a significant difficulty for the proposed mechanism is the strength of the singlet line at 6678A. Compared to the corresponding triplets, singlet lines are weak because of the loss of excitation when photons emitted in decays to the ground state ionize hydrogen atoms, an effect absent in the hydrogen-free atmospheres of Type Ib SNe.

Accepted for publication in A&A

References in corpus (7)

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