Identification of the High-Energy Gamma-Ray Source 3FGL J1544.6-1125 as a Transitional Millisecond Pulsar Binary in an Accreting State

Understand

We present X-ray, ultraviolet, and optical observations of 1RXS J154439.4-112820, the most probable counterpart of the unassociated Fermi LAT source 3FGL J1544.6-1125.

• The optical data reveal rapid variability, which is a feature of accreting systems.
• The X-rays exhibit large-amplitude variations in the form of fast switching (within ~10 s) between two distinct flux levels that differ by a factor of $\approx$10.
• The detailed optical and X-ray behavior is virtually identical to that seen in the accretion-disk-dominated states of the transitional millisecond pulsar binaries PSR J1023+0038 and XSS J12270-4859, which are also associated with $\gamma$-ray sources.