scholarly journals The Magnetic Corona: Magnetic Reconnection in Solar Flares

2004 ◽  
Vol 219 ◽  
pp. 91-102
Author(s):  
Harry P. Warren
Keyword(s):  
Spatial Resolution ◽  
Solar Flares ◽  
Light Curves ◽  
Small Scale ◽  
Flare Loop ◽  
X Ray ◽  
Stellar Flares ◽  
Emission Models ◽  
Reconnection Model ◽  
High Cadence

The ability of the Transition Region and Coronal Explorer (TRACE) to image the Sun at high spatial resolution and high cadence over a very broad range of temperatures makes it a unique instrument for observing solar flare plasma. TRACE observations have confirmed the reconnection model for solar flares, at least qualitatively. TRACE flare observations show impulsive footpoint brightenings that are followed by the formation of high-temperature loops in the corona. These loops then cool to lower temperatures, forming post-flare loop arcades. Comparisons between TRACE and lower spatial resolution Yohkoh Soft X-Ray Telescope (SXT) observations have revealed that solar flares are composed of a multitude of fine coronal loops. Detailed hydrodynamic modeling of flare light curves shows that this fine scale structuring is crucial to understanding the evolution of the observed emission. Models based on single, isothermal loops are not consistent with the TRACE observations. Models based on the sequential heating of small-scale loops, in contrast, are able to reproduce many of the salient features of the observed light curves. We will discuss the implication of these results for more energetic stellar flares as well as smaller-scale events that may be responsible for the heating of solar active region loops.

scholarly journals Hydrodynamic Models of Solar and Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 289-298
Author(s):  
Giovanni Peres
Keyword(s):  
High Resolution ◽  
Light Curve ◽  
Solar Flares ◽  
Impulsive Phase ◽  
Light Curves ◽  
Physical Parameters ◽  
The Sun ◽  
Hydrodynamic Models ◽  
X Ray ◽  
Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

scholarly journals Spikey: self-lensing flares from eccentric SMBH binaries

2020 ◽  
Vol 495 (4) ◽  
pp. 4061-4070 ◽  
Author(s):  
Betty X Hu ◽  
Daniel J D’Orazio ◽  
Zoltán Haiman ◽  
Krista Lynne Smith ◽  
Bradford Snios ◽  
...  
Keyword(s):  
Rest Frame ◽  
Relativistic Effects ◽  
Light Curves ◽  
Optical Data ◽  
Spectral Slope ◽  
X Ray ◽  
Periodic Behaviour ◽  
Black Hole Binary ◽  
High Cadence ◽  
Rule Out

ABSTRACT We examine the light curves of two quasars, motivated by recent suggestions that a supermassive black hole binary (SMBHB) can exhibit sharp lensing spikes. We model the variability of each light curve as due to a combination of two relativistic effects: the orbital relativistic Doppler boost and gravitational binary self-lensing. In order to model each system, we extend previous Doppler plus self-lensing models to include eccentricity. The first quasar is identified in optical data as a binary candidate with a 20-yr period (Ark 120), and shows a prominent spike. For this source, we rule out the lensing hypothesis and disfavour the Doppler-boost hypothesis due to discrepancies in the measured versus recovered values of the binary mass and optical spectral slope. The second source, which we nickname Spikey, is the rare case of an active galactic nucleus identified in Kepler’s high-quality, high-cadence photometric data. For this source, we find a model, consisting of a combination of Doppler modulation and a narrow symmetric lensing spike, consistent with an eccentric SMBHB with a mass of $M_{\text{tot}} = 3\times 10^{7} {\, \mathrm{M}_{\odot }}$, rest-frame orbital period T = 418 d, eccentricity e = 0.5, and seen at an inclination of 8○ from edge-on. This interpretation can be tested by monitoring Spikey for periodic behaviour and recurring flares in the next few years. In preparation for such monitoring, we present the first X-ray observations of this object taken by the Neil Gehrels Swift Observatory.

X-ray Spectral Synthesis in Hydrodynamic Flare Models

1990 ◽  
Vol 115 ◽  
pp. 126-131
Author(s):  
S. Serio ◽  
E. Antonucci ◽  
M.A. Dodero ◽  
G. Peres ◽  
F. Reale
Keyword(s):  
Solar Flares ◽  
Energy Deposition ◽  
Electron Beams ◽  
Spectral Synthesis ◽  
Theoretical Models ◽  
Hydrodynamic Models ◽  
X Ray ◽  
Relativistic Electron Beams ◽  
Stellar Flares ◽  
Magnetically Confined

AbstractCompact solar flares are triggered by sudden energy release in magnetically confined plasma. This class of flares is well suited to be studied with numerical hydrodynamic models. In particular, one can compare the evolution of observed and synthetic X-ray spectra, computed under various assumptions for the mechanism of impulsive energy deposition, to constrain theoretical models and their parameter space. We discuss recent results on solar flares along this line, non thermal to models of energy depositions by relativistic electron beams. We shall also discuss possible applications of X-ray spectral synthesis to stellar flares.

scholarly journals Long-Duration Solar and Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 313-322
Author(s):  
Giannina Poletto
Keyword(s):  
Solar Flares ◽  
Classification Scheme ◽  
High Spatial Resolution ◽  
Physical Parameters ◽  
Additional Information ◽  
Stellar Flares ◽  
Long Duration ◽  
Model Predictions ◽  
Flare Region ◽  
Reconnection Model

AbstractAccording to one of the most popular classifications, solar flares may be assigned either to the category of small short-lived events, or to the category of large, long-duration two-ribbon (2-R) flares. Even if such a broad division oversimplifies the flare phenomenon, our knowledge of the characteristics of stellar flares is so poor, that it is worthwhile to investigate the possibility of adopting this classification scheme for stellar flares as well. In particular we will analyze Einstein observations of a long duration flare on EQ Peg to establish whether it might be considered as a stellar analogy of 2-R solar events. To this end we apply to EQ Peg data a reconnection model, developed originally for solar 2-R flares, and conclude that stellar observations are consistent with model predictions, although additional information is required to identify uniquely the physical parameters of the flare region. Application of the model to integrated observations of a 2-R solar flare, for which high spatial resolution data are also available, shows, however, that future integrated observations may allow us to solve the ambiguities of the model and use it as a diagnostic tool for a better understanding of stellar flares.

scholarly journals Stellar flare diagnostics from multi–wavelength observations

2009 ◽  
Vol 5 (S264) ◽  
pp. 288-291 ◽  
Author(s):  
Alexander V. Stepanov ◽  
Yuri T. Tsap ◽  
Yulia G. Kopylova
Keyword(s):  
Scaling Law ◽  
Electric Circuit ◽  
Plasma Parameters ◽  
Stellar Flare ◽  
Flare Loop ◽  
X Ray ◽  
Stellar Flares ◽  
Flare Loops ◽  
Red Dwarfs ◽  
Multi Wavelength

AbstractQuasi–periodic pulsations in various wavebands are natural manifestations of emission of stellar flares. We suggest a diagnostic tool of stellar flares based on the coronal seismology and the solar–stellar analogy. Two approaches are used: (I) flare loop as a resonator for MHD oscillations and (II) flare loop as an equivalent electric circuit. Using optical, X–ray, and radio data we obtained flare plasma parameters for the red dwarfs EQ Peg, AT Mic, and AD Leo. The characteristic length of stellar flare loops l ~ R* and their electric currents turned out to be one–two orders of magnitude lager than the solar ones. Advantages of proposed diagnostics in comparison to the scaling law methods are given.

scholarly journals Preflare very long-periodic pulsations observed in Hα emission before the onset of a solar flare

2020 ◽  
Vol 639 ◽  
pp. L5
Author(s):  
Dong Li ◽  
Song Feng ◽  
Wei Su ◽  
Yu Huang
Keyword(s):  
Solar Flare ◽  
Light Curve ◽  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Light Curves ◽  
Trigger Mechanism ◽  
X Ray ◽  
Hα Emission ◽  
Plasma Loop ◽  
Full Disk

Context. Very long-periodic pulsations during preflare phases (preflare-VLPs) have been detected in the full-disk solar soft X-ray (SXR) flux. They may be regarded as precursors to solar flares and may help us better understand the trigger mechanism of solar flares. Aims. In this Letter, we report a preflare-VLP event prior to the onset of an M1.1 circular-ribbon flare on 2015 October 16. It was simultaneously observed in Hα, SXR, and extreme ultraviolet (EUV) wavelengths. Methods. The SXR fluxes in 1−8 Å and 1−70 Å were recorded by the Geostationary Operational Environmental Satellite (GOES) and Extreme Ultraviolet Variability Experiment, respectively; the light curves in Hα and EUV 211 Å were integrated over a small local region, which were measured by the 1 m New Vacuum Solar Telescope and the Atmospheric Imaging Assembly (AIA), respectively. The preflare-VLP is identified as the repeat and quasi-periodic pulses in light curves during preflare phase. The quasi-periodicity can be determined from the Fourier power spectrum with Markov chain Monte Carlo-based Bayesian. Results. Seven well-developed pulses are found before the onset of an M1.1 circular-ribbon flare. They are firstly seen in the local light curve in Hα emission and then discovered in full-disk SXR fluxes in GOES 1−8 Å and ESP 1−70 Å, as well as the local light curve in AIA 211 Å. These well-developed pulses can be regarded as the preflare-VLP, which might be modulated by LRC-circuit oscillation in the current-carrying plasma loop. The quasi-period is estimated to be ∼9.3 min. Conclusions. We present the first report of a preflare-VLP event in the local Hα line and EUV wavelength, which could be considered a precursor of a solar flare. This finding should therefore prove useful for the prediction of solar flares, especially for powerful flares.

scholarly journals Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

2019 ◽  
Vol 622 ◽  
pp. A210 ◽  
Author(s):  
M. G. Guarcello ◽  
G. Micela ◽  
S. Sciortino ◽  
J. López-Santiago ◽  
C. Argiroffi ◽  
...  
Keyword(s):  
Time Evolution ◽  
Energy Budget ◽  
Solar Flares ◽  
Light Curves ◽  
Integrated Analysis ◽  
Electromagnetic Spectrum ◽  
The Sun ◽  
X Rays ◽  
X Ray ◽  
Different Ages

Context. Flares are powerful events ignited by a sudden release of magnetic energy which triggers a cascade of interconnected phenomena, each resulting in emission in different electromagnetic bands. In fact, in the Sun flares are observed across the whole electromagnetic spectrum. Multi-band observations of stellar flares are instead rare. This limits our ability to extend what we learn from solar flares to the case of flares occurring in stars with different properties. Aims. With the aim of studying flares in the 125-Myr-old stars in the Pleiades observed simultaneously in optical and X-ray light, we obtained new XMM-Newton observations of this cluster during the observations of Kepler K2 Campaign 4. The objective of this paper is to characterize the most powerful flares observed in both bands and to constrain the energy released in the optical and X-ray, the geometry of the loops, and their time evolution. We also aim to compare our results to existing studies of flares occurring in the Sun and stars at different ages. Methods. We selected bright X-ray/optical flares that occurred in 12 known members of the Pleiades from their K2 and XMM-Newton light curves. The sample includes ten K-M stars, one F9 star, and one G8 star. Flare average properties were obtained from integrated analysis of the light curves during the flares. The time evolution of the plasma in the magnetic loops is constrained with time-resolved X-ray spectral analysis. Results. Most of the flares studied in this work emitted more energy in optical than in X-rays, as in most solar flares, even if the Pleiades flares output a larger fraction of their total energy in X-rays than typical solar flares do. Additionally, the energy budget in the two bands is weakly correlated. We also found comparable flare duration in optical and X-rays and observed that rapidly rotating stars (e.g., with rotation period shorter than 0.5 days) preferentially host short flares. We estimated the slope of the cooling path of the flares in the log(EM)-vs.-log(T) plane. The values we obtained are affected by large uncertainties, but their nominal values suggest that the flares analyzed in this paper are mainly due to single loops with no sustained heating occurring during the cooling phase. We also observed and analyzed oscillations with a period of 500 s during one of the flares. Conclusions. The flares observed in the Pleiades can be classified as “superflares” based on their energy budget in the optical, and share some of the properties of the flares observed in the Sun, despite being more energetic. For instance, as in most solar flares, more energy is typically released in the optical than in X-rays and the duration of the flares in the two bands is correlated. We have attempted a comparison between the X-ray flares observed in the Pleiades and those observed in clusters with different ages, but to firmly address any evolutionary pattern of flare characteristics, similar and uniform multi-wavelength analyses on more complete samples are necessary.

scholarly journals Models of Flaring Loops

1989 ◽  
Vol 104 (1) ◽  
pp. 105-115
Author(s):  
A. Gordon Emslie
Keyword(s):  
Solar Flares ◽  
Energy Transport ◽  
High Energy ◽  
Loop Structure ◽  
Predominant Role ◽  
Release Process ◽  
Flare Loop ◽  
X Ray ◽  
Physical Mechanisms ◽  
High Energy Electrons

AbstractWe review the somewhat questionable concept of an isolated flare loop and the various physical mechanisms believed to be responsible, to some degree, for energy transport within the loop structure. Observational evidence suggests a predominant role for high-energy electrons as an energy transport mechanism, and we explore the consequences of such a scenario in some detail, focusing on radiation signatures in the soft X-ray, hard X-ray, and EUV wavebands, as observed by recent satellite observatories. We find that the predictions of flare loop models are in fact in excellent agreement with these observations, reinforcing both the notion of the loop as a fundamental component of solar flares and the belief that electron acceleration is an integral part of the flare energy release process.

scholarly journals Balmer and soft X-ray emission from solar and stellar flares

1990 ◽  
Vol 137 ◽  
pp. 153-157
Author(s):  
C. J. Butler
Keyword(s):  
Solar Flares ◽  
The Sun ◽  
X Ray ◽  
Stellar Flares ◽  
Basic Similarity ◽  
Good Agreement

Integrated soft X-ray (8-12A) fluxes for solar flares have been scaled to the equivalent EXOSAT fluxes using spectra obtained from a variety of rocket-based experiments. The data show good agreement with the soft X-ray - Hγ correlation established by Butler et al. (1988) for stellar flares and confirm the basic similarity, in this respect, of flares on the Sun to those on dMe stars.

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