Variable Heating and Flaring of Three Redback Millisecond Pulsar Companions

Understand

We are monitoring established and putative redback millisecond pulsars (MSPs) in time-series photometry, repeatedly covering their 5-6 hr orbital light curves in $r^{\prime}$ or $R$.

• On timescales of months, PSR J1048+2339 and XMMU J083850.38$-$282756.8 exhibit similar variability of $\approx0.3$ mag on the heated side of the companion star.
• However, the heating light curve is rarely symmetric, suggesting that the intrabinary shock generated by the pulsar wind is skewed in addition to being variable, or that changing magnetic fields intrinsic to the companion channel the pulsar wind.
• In addition to this variable heating, there are long-lived flaring states that increase the brightness by an additional 0.5 mag, with variability on $\approx10$ minute timescales.