Optical photometry of two transitional millisecond pulsars in the radio pulsar state

ABSTRACT We present ULTRACAM multiband optical photometry of two transitional millisecond pulsars (tMSPs), PSR J1023+0038 and J1227−4853, taken while both were in their radio pulsar states. The light curves show significant asymmetry about the flux maxima all observed bands, suggesting an asymmetric source heating system. model using icarus binary code, models with additional ‘hotspot’ contribution anisotropic heat redistribution to treat asymmetry. Our modelling reveals companion stars underfilled Roche lobes PSRs lobe filling factors range f ∼ 0.82−0.92. While volume-averaged are closer unity, underfilling is unexpected from tMSPs as they must rapidly overfill start transferring mass, which occurs on time-scale weeks or months. discuss motivation validity our extensions implications lobe, suggest future work further investigate role factor tMSP cycle.