Understanding the X-ray Flaring from Eta Car

TL;DR

This study analyzes X-ray flares from Eta Carinae over three orbital cycles, suggesting that stochastic wind clumps are the most consistent explanation for the observed rapid brightness variations.

Contribution

It provides the first detailed quantification of Eta Carinae's X-ray flares and proposes a novel model involving homologously expanding wind clumps to explain the variability.

Findings

Flares are shorter and more frequent near periastron.

Largest flares maintain similar strength across phases.

Clump distribution follows a turbulence-like power law.

Abstract

We quantify the rapid variations in X-ray brightness ("flares") from the extremely massive colliding wind binary Eta Carinae seen during the past three orbital cycles by RXTE. The observed flares tend to be shorter in duration and more frequent as periastron is approached, although the largest ones tend to be roughly constant in strength at all phases. Plausible scenarios include (1) the largest of multi-scale stochastic wind clumps from the LBV component entering and compressing the hard X-ray emitting wind-wind collision (WWC) zone, (2) large-scale corotating interacting regions in the LBV wind sweeping across the WWC zone, or (3) instabilities intrinsic to the WWC zone. The first one appears to be most consistent with the observations, requiring homologously expanding clumps as they propagate outward in the LBV wind and a turbulence-like power-law distribution of clumps, decreasing in number towards larger sizes, as seen in Wolf-Rayet winds.