3 years ago

The first continuous optical monitoring of the transitional millisecond pulsar PSR J1023+0038 with Kepler.

E. de Oña Wilhelmi, D. F. Torres, D. de Martino, L. Stella, F. Coti Zelati, N. Rea, A. Papitto, S. Campana, C. Knigge, G.L. Israel, S. Scaringi, P. D'Avanzo, A. Serenelli

We report on the first continuous, 80 days-long, optical monitoring of the transitional millisecond pulsar PSR J1023+0038 carried out in mid-2017 with Kepler in the K2 configuration, when an X-ray sub-luminous accretion disk was present in the binary. Flares lasting from minutes to 14 hours were observed for 15.6% of the time, a larger fraction than previously reported on the basis of X-ray and past optical observations, more frequently when the companion was at the superior conjunction of the orbit. A sinusoidal modulation at the binary orbital period was also present with an amplitude of ~16%, which varied by a few percent over timescales of days, and whose maximum took place 890 +/- 85 s earlier than the superior conjunction of the donor. We interpret these phenomena in terms of reprocessing of the X-ray emission by an asymmetrically heated companion star surface and/or a non-axisymmetric outflow possibly launched close to the inner Lagrangian point. Furthermore, the non-flaring average emission varied by up to ~ 40% over a time scale of days in the absence of correspondingly large variations of the irradiating X-ray flux. The latter suggests that the observed changes in the average optical luminosity might be due to variations of the geometry, size and/or mass accretion rate in the outer regions of the accretion disk.

Publisher URL: http://arxiv.org/abs/1801.04736

DOI: arXiv:1801.04736v1

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