Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system ϵ Lupi

Abstract

We report detailed X-ray observations of the unique binary system ε Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbital and magnetic properties of the system imply that the magnetospheres overlap at all orbital phases, suggesting the possibility of variable inter-star magnetospheric interaction due to the non-negligible eccentricity of the orbit. To investigate this effect, we observed the X-ray emission from ε Lupiboth near and away from periastron passage, using the Neutron Star Interior Composition Explorer mission (NICER) X-ray Telescope. We find that the system produces excess X-ray emission at the periastron phase, suggesting the presence of variable inter-star magnetospheric interaction. We also discover that the enhancement at periastron is confined to a very narrow orbital phase range ($\approx 5~{{\%}}$ of the orbital period), but the X-ray properties close to periastron phase are similar to those observed away from periastron. From these observations, we infer that the underlying cause is magnetic reconnection heating the stellar wind plasma, rather than shocks produced by wind-wind collision. Finally, by comparing the behavior of ε Lupiwith that observed for cooler magnetic binary systems, we propose that elevated X-ray flux at periastron phase is likely a general characteristic of interacting magnetospheres irrespective of the spectral types of the constituent stars.

X-Ray, Near-ultraviolet, and Optical Flares Produced by Colliding Magnetospheres in the Young High-eccentricity Binary DQ Tau

“…Additionally, the authors discuss the replenishment of this magnetic energy through the combined effects of the orbital and spin motions of the binary components. Adams et al (2011) and Das et al (2023) have determined that this magnetic model yields reasonable estimates of the magnetic reconnection energy responsible for powering the radio and X-ray flares observed near the periastra of the V773 Tau and ò Lupi eccentric binaries, respectively.…”

“…Several other young binary systems with high eccentricities have been reported to exhibit enhanced levels of X-ray, optical/millimeter, or radio emissions near their periastron passages. Notable examples include ò Lupi (Das et al 2023), a collective study of four binaries (Parenago 523, RX J1622.7-2325 Nw, UZ Tau E, and HD 152404) conducted by Getman et al (2016), UZ Tau E (Kóspál et al 2011), and V773 Tau A (Massi et al 2008;Adams et al 2011). In these systems, magnetosphere collision has been proposed as a primary mechanism responsible for generating the magnetic reconnection energy that drives these events.…”