Superorbital modulation of X-ray emission from gamma-ray binary LSI +61 303

TL;DR

This study reveals a consistent time lag between X-ray and radio flares in gamma-ray binary LSI +61 303, linked to plasma blob formation and travel, with implications for understanding high-energy astrophysical processes.

Contribution

It uncovers a persistent phase lag between X-ray and radio emissions and proposes a new model for plasma blob formation and propagation in the system.

Findings

X-ray flare phases vary over a 4.6-year superorbital cycle.

Radio flares lag X-ray flares by approximately 0.2 in phase.

The phase lag corresponds to plasma blob travel time within the binary system.

Abstract

We report the discovery of a systematic constant time lag between the X-ray and radio flares of the gamma-ray binary LSI +61 303, persistent over long, multi-year, time scale. Using the data of monitoring of the system by RXTE we show that the orbital phase of X-ray flares from the source varies from $\phi_X\simeq 0.35$ to $\phi_X\simeq 0.75$ on the superorbital 4.6 yr time scale. Simultaneous radio observations show that periodic radio flares always lag the X-ray flare by $\Delta\phi_{X-R}\simeq 0.2$. We propose that the constant phase lag corresponds to the time of flight of the high-energy particle filled plasma blobs from inside the binary to the radio emission region at the distance ~10 times the binary separation distance. We put forward a hypothesis that the X-ray bursts correspond to the moments of formation of plasma blobs inside the binary system.