TY - JOUR
T1 - Solar flare hard X-ray spikes observed by RHESSI
T2 - A statistical study
AU - Cheng, J. X.
AU - Qiu, J.
AU - Ding, M. D.
AU - Wang, Haimin
N1 - Funding Information: We thank the referee for constructive comments that help improve the presentation. We thank G. J. Hurford for help with the demodulation. Part of this work was conducted during the Research Experience for Undergraduates (REU) program supported by National Science Foundation through grant ATM-0552958 contracted to Montana State University. This work was supported by the Scientific Research Foundation of Graduate School of Nanjing University, FANEDD under grant 200226, NSFC under grants 10878002, 10933003, 11133004 and 11103008, NKBRSF under grant 2011CB811402, the Chinese Academy of Sciences (KZZD-EW-01-3), and US NASA grant NNX08AE44G.
PY - 2012
Y1 - 2012
N2 - Context. Hard X-ray (HXR) spikes refer to fine time structures on timescales of seconds to milliseconds in high-energy HXR emission profiles during solar flare eruptions. Aims. We present a preliminary statistical investigation of temporal and spectral properties of HXR spikes. Methods. Using a three-sigma spike selection rule, we detected 184 spikes in 94 out of 322 flares with significant counts at given photon energies, which were detected from demodulated HXR light curves obtained by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). About one fifth of these spikes are also detected at photon energies higher than 100 keV. Results. The statistical properties of the spikes are as follows. (1) HXR spikes are produced in both impulsive flares and long-duration flares with nearly the same occurrence rates. Ninety percent of the spikes occur during the rise phase of the flares, and about 70% occur around the peak times of the flares. (2) The time durations of the spikes vary from 0.2 to 2 s, with the mean being 1.0 s, which is not dependent on photon energies. The spikes exhibit symmetric time profiles with no significant difference between rise and decay times. (3) Among the most energetic spikes, nearly all of them have harder count spectra than their underlying slow-varying components. There is also a weak indication that spikes exhibiting time lags in high-energy emissions tend to have harder spectra than spikes with time lags in low-energy emissions.
AB - Context. Hard X-ray (HXR) spikes refer to fine time structures on timescales of seconds to milliseconds in high-energy HXR emission profiles during solar flare eruptions. Aims. We present a preliminary statistical investigation of temporal and spectral properties of HXR spikes. Methods. Using a three-sigma spike selection rule, we detected 184 spikes in 94 out of 322 flares with significant counts at given photon energies, which were detected from demodulated HXR light curves obtained by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). About one fifth of these spikes are also detected at photon energies higher than 100 keV. Results. The statistical properties of the spikes are as follows. (1) HXR spikes are produced in both impulsive flares and long-duration flares with nearly the same occurrence rates. Ninety percent of the spikes occur during the rise phase of the flares, and about 70% occur around the peak times of the flares. (2) The time durations of the spikes vary from 0.2 to 2 s, with the mean being 1.0 s, which is not dependent on photon energies. The spikes exhibit symmetric time profiles with no significant difference between rise and decay times. (3) Among the most energetic spikes, nearly all of them have harder count spectra than their underlying slow-varying components. There is also a weak indication that spikes exhibiting time lags in high-energy emissions tend to have harder spectra than spikes with time lags in low-energy emissions.
KW - Sun: X-rays gamma rays
KW - Sun: flares
UR - https://www.scopus.com/pages/publications/84868318865
UR - https://www.scopus.com/pages/publications/84868318865#tab=citedBy
U2 - 10.1051/0004-6361/201118608
DO - 10.1051/0004-6361/201118608
M3 - Article
SN - 0004-6361
VL - 547
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A73
ER -