Delayed Development of Cool Plasmas in X-ray Flares from kappa1 Ceti

Thumbnail Image

Files

2301.01377.pdf (2.51 MB)

Links to Files

https://arxiv.org/abs/2301.01377

Permanent Link

https://doi.org/10.48550/arXiv.2301.01377
 http://hdl.handle.net/11603/26764

Collections

UMBC Physics Department
UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
UMBC Faculty Collection

Author/Creator

Author/Creator ORCID

https://orcid.org/0000-0001-7515-2779

Date

2023-01-03

Type of Work

journal articles
preprints
Text

Department

Program

Citation of Original Publication

Rights

This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Public Domain Mark 1.0

Subjects

Abstract

he Neutron star Interior Composition ExploreR (NICER) X-ray observatory observed two powerful X-ray flares equivalent to superflares from the nearby young solar-like star, κ 1 Ceti, in 2019. NICER follows each flare from the onset through the early decay, collecting over 30 cnts s−1 near the peak, enabling a detailed spectral variation study of the flare rise. The flare in September varies quickly in ∼800 sec, while the flare in December has a few times longer timescale. In both flares, the hard band (2−4 keV) light curves show typical stellar X-ray flare variations with a rapid rise and slow decay, while the soft X-ray light curves, especially of the September flare, have prolonged flat peaks. The time-resolved spectra require two temperature plasma components at kT ∼0.3−1 keV and ∼2−4 keV. Both components vary similarly, but the cool component lags by ∼200 sec with a 4−6 times smaller emission measure (EM) compared to the hot component. A comparison with hydrodynamic flare loop simulations indicates that the cool component originates from X-ray plasma near the magnetic loop footpoints, which mainly cools via thermal conduction. The time lag represents the travel time of the evaporated gas through the entire flare loop. The cool component has several times smaller EM than its simulated counterpart, suggesting a suppression of conductive cooling possibly by the expansion of the loop cross-sectional area or turbulent fluctuations. The cool component’s time lag and small EM ratio provide important constraints on the flare loop geometry.