The First Continuous Optical Monitoring of the Transitional Millisecond Pulsar PSR J1023+0038 with Kepler

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

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12 Scopus citations


We report on the first continuous, 80-day 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 subluminous accretion disk was present in the binary. Flares lasting from minutes to 14 hr were observed for 15.6% of the time, which is a larger fraction than previously reported on the basis of X-ray and past optical observations, and more frequently when the companion was at 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 with a maximum that took place 890 ±85 s earlier than the superior conjunction of the donor. We interpret this 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 timescale 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.

Original languageEnglish
Article numberL12
JournalAstrophysical Journal Letters
Issue number2
StatePublished - May 10 2018


  • X-rays: binaries
  • pulsars: individual (PSR J1023+0038)
  • stars: neutron


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