X-Ray Superflares on CC Eri

Abstract

We present an in-depth study of two superflares (F1 and F2) detected on an active binary star CC Eridani by the Swift observatory. These superflares triggered the Burst Alert Telescope (BAT) in the hard X-ray band on 2008 October 16 and 2012 February 24. The rise phases of both the flares were observed only with BAT, whereas the decay phases were observed simultaneously with the X-ray Telescope. It has been found that the flares decay faster in the hard X-ray band than in the soft X-ray band. Both flares F1 and F2 are highly energetic with respective peak X-ray luminosities of $\sim$$10^{32.2}$ and $\sim$$10^{31.8}$ erg s${}^{-1}$ in 0.3--50 keV energy band, which are larger than any other flares previously observed on CC Eri. The time-resolved spectral analysis during the flares shows the variation in the coronal temperature, emission measure, and abundances. The elemental abundances are enhanced by a factor of $\sim$8 to the minimum observed in the post-flare phase for the flare F1. The observed peak temperatures in these two flares are found to be 174 MK and 128 MK. Using the hydrodynamic loop modeling, we derive loop lengths for both the flares as 1.2$\pm$0.1$\times$10${}^{10}$ cm and 2.2$\pm$0.6$\times$10${}^{10}$ cm, respectively. The Fe K$\alpha$ emission at 6.4 keV is also detected in the X-ray spectra and we model the K$\alpha$ emission feature as fluorescence from the hot flare source irradiating the photospheric iron. These superflares are the brightest, hottest, and shortest in duration observed thus far on CC Eri.

References in corpus (11)

• Diagnostics of stellar flares from X-ray observations: from the decay to the rise phase
• Nonthermal Hard X-ray Emission and Iron Kalpha Emission from a Superflare on II Pegasi
• A Very Bright, Very Hot, and Very Long Flaring Event from the M Dwarf Binary System DG CVn
• A study of X-ray flares - I. Active late-type dwarfs
• Modelling the spectral response of the Swift-XRT CCD camera: Experience learnt from in-flight calibration
• X-ray Fluorescent Fe Kalpha Lines from Stellar Photospheres
• Six Large Coronal X-ray Flares Observed With Chandra
• A prompt radio transient associated with a gamma-ray superflare from the young M dwarf binary DG CVn
• Geometry Diagnostics of a Stellar Flare from Fluorescent X-rays
• X-ray flares on the UV Ceti-type star CC Eridani: a "peculiar" time-evolution of spectral parameters
• Fe K alpha and hydrodynamic loop model diagnostics for a large flare on II Peg