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Paper: The Optical Counterpart of SAX J1808.4-3658 in Quiescence: Evidence of an Active Radio Pulsar?
Volume: 328, Binary Radio Pulsars
Page: 295
Authors: Di Salvo, T.; Robba, N.; Burderi, L.; D'Antona, F.; Testa, V.
Abstract: The optical counterpart of the binary millisecond X-ray pulsar SAX J1808.4−3658 during quiescence was detected at V = 21.5 mag, inconsistent with intrinsic emission from the faint companion star. We propose that the optical emission from this system during quiescence is due to the reprocessing by the companion star and a remnant accretion disk of the rotational energy released by the fast spinning neutron star, switched on, as magneto-dipole rotator (radio pulsar), during quiescence. In this scenario the companion behaves as a bolometer, reprocessing in optical the intercepted fraction of the power emitted by the pulsar. Our computations indicate that the observed optical magnitudes are fully consistent with this hypothesis. In this case the observed optical luminosity may be the first evidence that a radio pulsar is active in this system during quiescence.
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