To be Submitted to the Astrophysical Journal Understanding the X-ray Flaring from n Carinae A. F. J. Moffat Departement de physique, UniversiM de Montreal, Succursale Centre-Ville, Montreal, QC, H3C V7, and Centre de recherche en astrophysique du Quebec, Canada
[email protected] M. F. Corcoranl CRESST and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, jWD 20771, USA
[email protected] ABSTRACT We quantify the rapid variations in X-ray brightness ( "flares") from the ex- tremely massive colliding wind binary n Carinae seen during the past three or- bital 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. Subject headings: X-rays: stars — stars: early-type — stars: individual (p Car) — stars: LBV 'Universities Space Research Association, 10211 W incopin Circle. Suite 500 Columbia, 1v1D 21044, USA. -2— 1. Introduction The extremely massive binary star rl Carinae consists of a Luminous Blue Variable (LBV) primary (star A) coupled with a hot, fast-wind secondary (star B) which is probably an evolved 0 star (Verner et al.