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We present a statistical analysis of properties of Soft X-Ray (SXR) emission, plasma temperature (T), and emission measure (EM), derived from GOES observations of flares in 2002-2017. The temperature and emission measures are obtained using…

Solar and Stellar Astrophysics · Physics 2019-03-27 Viacheslav M Sadykov , Alexander G Kosovichev , Irina N Kitiashvili , Alexander Frolov

We present observations of the occulted active region AR12222 during the third {\em NuSTAR} solar campaign on 2014 December 11, with concurrent {\em SDO/}AIA and {\em FOXSI-2} sounding rocket observations. The active region produced a…

Aims: This work aims to identify the mechanism driving pulsations in hard X-ray (HXR) and microwave emission during solar flares. Here, by using combined HXR and microwave observations from Solar Orbiter/STIX and EOVSA we investigate an…

Solar and Stellar Astrophysics · Physics 2024-05-01 Hannah Collier , Laura A. Hayes , Sijie Yu , Andrea F. Battaglia , William Ashfield , Vanessa Polito , Louise K. Harra , Säm Krucker

Context. We present an analysis of a GOES M1.8 flare with excellent observational coverage in UV, EUV, and X-ray, including observations from the instruments IRIS, SDO with AIA, Hinode/EIS, Hinode/XRT, and Solar Orbiter with the…

Small-scale impulsive events, known as nanoflares, are thought to be one of the prime candidates that can keep the solar corona hot at its multi-million Kelvin temperature. Individual nanoflares are difficult to detect with the current…

Solar flares result from the rapid conversion of stored magnetic energy within the Sun's corona. These energy releases are associated with coronal magnetic loops, which are rooted in dense photospheric plasma and are passively transported…

Solar and Stellar Astrophysics · Physics 2025-03-28 M. Berretti , S. Mestici , L. Giovannelli , D. Del Moro , M. Stangalini , F. Giannattasio , F. Berrilli

The 2014 March 29 X1 solar flare (SOL20140329T17:48) produced bright continuum emission in the far- and near-ultraviolet (NUV) and highly asymmetric chromospheric emission lines, providing long-sought constraints on the heating mechanisms…

Solar and Stellar Astrophysics · Physics 2017-02-17 Adam F. Kowalski , Joel C. Allred , Adrian N. Daw , Gianna Cauzzi , Mats Carlsson

Ever-increasing multi-frequency imaging of solar observations suggests that solar flares often involve more than one magnetic fluxtube. Some of the fluxtubes are closed, while others can contain open field. The relative proportion of…

Solar and Stellar Astrophysics · Physics 2017-08-30 Gregory D. Fleishman , Gelu M. Nita , Dale E. Gary

Nanoflares are regarded as one of the major mechanisms of magnetic energy release and coronal heating in the solar outer atmosphere. We conduct a statistical study on the response of the chromosphere and transition region to nanoflares, as…

Solar and Stellar Astrophysics · Physics 2023-03-29 Kyuhyoun Cho , Paola Testa , Bart De Pontieu , Vanessa Polito

Decades of astrophysical observations have convincingly shown that soft X-ray (SXR; ~0.1--10 keV) emission provides unique diagnostics for the high temperature plasmas observed in solar flares and active regions. SXR observations critical…

Instrumentation and Methods for Astrophysics · Physics 2017-01-04 Amir Caspi , Albert Y. Shih , Harry P. Warren , Marek Stęślicki , Janusz Sylwester

A complete understanding of the onset and subsequent evolution of confined flares has not been achieved. Earlier studies mainly analyzed disk events so as to reveal their magnetic topology and cause of confinement. In this study, taking…

Solar and Stellar Astrophysics · Physics 2018-03-14 Hao Ning , Yao Chen , Zhao Wu , Yang Su , Hui Tian , Gang Li , Guohui Du , Hongqiang Song

Solar flare hard X-ray spectroscopy serves as a key diagnostic of the accelerated electron spectrum. However, the standard approach using the collisional cold thick-target model poorly constrains the lower-energy part of the accelerated…

Solar and Stellar Astrophysics · Physics 2019-02-05 Eduard P. Kontar , Natasha L. S. Jeffrey , A. Gordon Emslie

Nanoflares, the basic unit of impulsive energy release may produce much of the solar background emission. Extrapolation of the energy frequency distribution of observed microflares, which follows a power law to lower energies can give an…

Solar and Stellar Astrophysics · Physics 2011-12-22 E. Tajfirouze , H. Safari

3He-rich solar energetic particles (SEPs) are believed to be accelerated in solar flares or jets by a mechanism that depends on the ion charge-to-mass (Q/M) ratio. It implies that the flare plasma characteristics (e.g., temperature) may be…

Solar and Stellar Astrophysics · Physics 2021-03-10 R. Bucik , S. M. Mulay , G. M. Mason , N. V. Nitta , M. I. Desai , M. A. Dayeh

We investigated the three-dimensional (3D) magnetic structures and dynamics responsible for particle acceleration in an X7.1-class flare that occurred on October 1, 2024, in NOAA active region 13842. We combined stereoscopic hard X-ray…

Solar and Stellar Astrophysics · Physics 2026-02-11 Keitarou Matsumoto , Satoshi Inoue , Meiqi Wang , Säm Krucker , Satoshi Masuda , Muriel Zoë Stiefel , Jeongwoo Lee , Bin Chen , Haimin Wang

The thermal-to-nonthermal partition was found to vary greatly from one flare to another resulting in a broad variety of cases from 'heating without acceleration' to 'acceleration without heating'. Recent analysis of microwave data of these…

Solar and Stellar Astrophysics · Physics 2013-04-02 Gregory D. Fleishman

We investigate the influence of the variations of energy spectrum of non-thermal electrons on the resulting GOES classes of solar flares. Twelve observed flares with various soft to hard X-ray emission ratios were modelled using different…

Solar and Stellar Astrophysics · Physics 2009-09-25 R. Falewicz , P. Rudawy , M. Siarkowski

Temporary enhancements of the coronal emission measure in a quiet region have been shown to constitute a significant energy input. Here some relatively large events are studied for simultaneous brightenings in transition region lines and in…

Astrophysics · Physics 2015-06-24 Sam Krucker , Arnold O. Benz

Context: Solar flares accelerate electrons, creating non-thermal energy distributions. However, the acceleration sites and dominant acceleration mechanisms remain largely unknown. Aims: We study the characteristics of electron acceleration…

Solar and Stellar Astrophysics · Physics 2025-11-12 Eilif S. Øyre , Boris V. Gudiksen , Lyndsay Fletcher

We present direct evidence for the detection of the main energy release site in a non-eruptive solar flare, SOL2013-11-09T06:38UT. This GOES C2.7 event was characterised by two flaring ribbons and a compact, bright coronal source located…

Solar and Stellar Astrophysics · Physics 2015-05-06 Paulo J. A. Simões , David R. Graham , Lyndsay Fletcher