scholarly journals The Model of the Impulsive Phase of Stellar Flares

1989 ◽  
Vol 104 (2) ◽  
pp. 297-300
Author(s):  
V.P. Grinin ◽  
V.V. Sobolev
Keyword(s):  
Radiative Transfer ◽  
Solar Flares ◽  
Charged Particles ◽  
Impulsive Phase ◽  
High Energy ◽  
Stellar Flares ◽  
Flare Region ◽  
Optical Continuum

AbstractThe arguments in favour of that the primary heating of the gas at the impulsive phase of stellar flares is caused by charged particles of higher energies than in the solar flares are given. It is shown that the model of the deep heating by high energy protons (E ≃ 10 MeV) or electrons (E ≃ 100 keV) with taken into account of the radiative transfer in flare region explane the main properties of the optical continuum of the flare.

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 White-light continuum in stellar flares

2015 ◽  
Vol 11 (S320) ◽  
pp. 259-267 ◽  
Author(s):  
Adam F. Kowalski
Keyword(s):  
White Light ◽  
High Energy ◽  
Continuum Emission ◽  
Nonthermal Electrons ◽  
White Light Continuum ◽  
Optical Wavelength ◽  
Near Ultraviolet ◽  
Stellar Flares ◽  
Optical Continuum ◽  
M Dwarf

AbstractIn this talk, we discuss the formation of the near-ultraviolet and optical continuum emission in M dwarf flares through the formation of a dense, heated chromospheric condensation. Results are used from a recent radiative-hydrodynamic model of the response of an M dwarf atmosphere to a high energy flux of nonthermal electrons. These models are used to infer the charge density and optical depth in continuum emitting flare layers from spectra covering the Balmer jump and optical wavelength regimes. Future modeling and observational directions are discussed.

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.

Characteristics of Sunquake Events Observed in Solar Cycle 24

2021 ◽  
Author(s):  
Alexander Kosovichev ◽  
Ivan Sharykin
Keyword(s):  
Solar Cycle ◽  
Solar Flares ◽  
Active Regions ◽  
Impulsive Phase ◽  
High Energy ◽  
Lower Atmosphere ◽  
Solar Dynamics Observatory ◽  
X Ray ◽  
Solar Cycle 24 ◽  
Cycle 24

<p>Helioseismic response to solar flares ("sunquakes") occurs due to localized force or/and momentum impacts observed during the flare impulsive phase in the lower atmosphere. Such impacts may be caused by precipitation of high-energy particles, downward shocks, or magnetic Lorentz force. Understanding the mechanism of sunquakes is a key problem of the flare energy release and transport. Our statistical analysis of M-X class flares observed by the Solar Dynamics Observatory during Solar Cycle 24 has shown that contrary to expectations, many relatively weak M-class flares produced strong sunquakes, while for some powerful X-class flares, helioseismic waves were not observed or were weak. The analysis also revealed that there were active regions characterized by the most efficient generation of sunquakes during the solar cycle. We found that the sunquake power correlates with maximal values of the X-ray flux derivative better than with the X-ray class. The sunquake data challenge the current theories of solar flares.</p>

Millimeter, Microwave, Hard X-Ray, and Soft X-Ray Observations of Energetic Electron Populations in Solar Flares

1994 ◽  
Vol 142 ◽  
pp. 599-610
Author(s):  
M. R. Kundu ◽  
S. M. White ◽  
N. Gopalswamy ◽  
J. Lim
Keyword(s):  
Solar Flares ◽  
Energetic Electron ◽  
Impulsive Phase ◽  
High Energy ◽  
X Rays ◽  
High Turnover ◽  
X Ray ◽  
Nonthermal Electrons ◽  
Time Profiles ◽  
Wavelength Emission

AbstractWe present comparisons of multiwavelength data for a number of solar flares observed during the major campaign of 1991 June. The different wavelengths are diagnostics of energetic electrons in different energy ranges: soft X-rays are produced by electrons with energies typically below 10 keV, hard X-rays by electrons with energies in the range 10-200 keV, microwaves by electrons in the range 100 keV-1 MeV, and millimeter-wavelength emission by electrons with energies of 0.5 MeV and above. The flares in the 1991 June active period were remarkable in two ways: all have very high turnover frequencies in their microwave spectra, and very soft hard X-ray spectra. The sensitivity of the microwave and millimeter data permit us to study the more energetic (>0.3 MeV) electrons even in small flares, where their high-energy bremsstrahlung is too weak for present detectors. The millimeter data show delays in the onset of emission with respect to the emissions associated with lower energy electrons and differences in time profiles, energy spectral indices incompatible with those implied by the hard X-ray data, and a range of variability of the peak flux in the impulsive phase when compared with the peak hard X-ray flux which is two orders of magnitude larger than the corresponding variability in the peak microwave flux. All these results suggest that the hard X-ray-emitting electrons and those at higher energies which produce millimeter emission must be regarded as separate populations. This has implications for the well-known “number problem” found previously when comparing the numbers of nonthermal electrons required to produce the hard X-ray and radio emissions.Subject headings: Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays

scholarly journals Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with the Seimei Telescope, SCAT, NICER, and OISTER

2020 ◽  
Vol 72 (4) ◽  
Author(s):  
Kosuke Namekata ◽  
Hiroyuki Maehara ◽  
Ryo Sasaki ◽  
Hiroki Kawai ◽  
Yuta Notsu ◽  
...  
Keyword(s):  
Emission Line ◽  
White Light ◽  
High Energy ◽  
Lower Atmosphere ◽  
Line Profiles ◽  
X Ray ◽  
Energy Beam ◽  
Stellar Flares ◽  
Optical Continuum ◽  
M Dwarf

Abstract We report on multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with the Seimei Telescope (6150–7930 Å), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700–7500 Å), and NICER (Neutron Star Interior Composition Explorer; 0.2–12.0 keV), with the collaboration of the OISTER (Optical and Infrared Synergetic Telescopes for Education and Research) program. Twelve flares are detected in total, including ten Hα, four X-ray, and four optical-continuum flares; one of them is a superflare with a total energy of ∼2.0 × 1033 erg. We found that: (1) during the superflare, the Hα emission line full width at 1/8 maximum dramatically increases to 14 Å from 8 Å in the low-resolution spectra (R ∼ 2000) accompanied by large white-light flares, (2) some weak Hα/X-ray flares are not accompanied by white-light emissions, and (3) the non-flaring emissions show clear rotational modulations in X-ray and Hα intensity in the same phase. To understand these observational features, one-dimensional hydrodynamic flare simulations are performed using the RADYN code. We find the simulated Hα line profiles with hard and high-energy non-thermal electron beams to be consistent with the initial phase line profiles of the superflares, while those with a softer and/or weak-energy beam are consistent with those in decay phases, indicating the changes in the energy fluxes injected to the lower atmosphere. Also, we find that the relation between the optical continuum and Hα intensity is nonlinear, which can be one cause of the non-white-light flares. The flare energy budget exhibits diversity in the observations and models, and more observations of stellar flares are necessary for constraining the occurrence of various emission line phenomena in stellar flares.

scholarly journals Numerical RHD simulations of flaring chromosphere with Flarix

2015 ◽  
Vol 11 (S320) ◽  
pp. 233-238 ◽  
Author(s):  
Petr Heinzel ◽  
Jana Kašparová ◽  
Michal Varady ◽  
Marian Karlický ◽  
Zdeněk Moravec
Keyword(s):  
Radiative Transfer ◽  
Solar Flares ◽  
Electron Beams ◽  
High Energy ◽  
Energy Electron ◽  
High Energy Electron ◽  
Conservation Equations ◽  
Continuum Radiation

AbstractFlarix is a radiation–hydrodynamical (RHD) code for modeling of the response of the chromosphere to a beam bombardment during solar flares. It solves the set of hydrodynamic conservation equations coupled with NLTE equations of radiative transfer. The simulations are driven by high energy electron beams. We present results of the Flarix simulations of a flaring loop relevant to the problem of continuum radiation during flares. In particular we focus on properties of the hydrogen Balmer continuum which was recently detected by IRIS.

scholarly journals Fermi Large Area Telescope observation of high-energy solar flares: constraining emission scenarios

2015 ◽  
Vol 11 (S320) ◽  
pp. 51-56
Author(s):  
Nicola Omodei ◽  
Melissa Pesce-Rollins ◽  
Vahè Petrosian ◽  
Wei Liu ◽  
Fatima Rubio da Costa ◽  
...  
Keyword(s):  
Solar Flares ◽  
Gamma Ray ◽  
Solar Energetic Particle ◽  
Cosmic Ray ◽  
Impulsive Phase ◽  
High Energy ◽  
Solar Energetic Particle Event ◽  
Emission Scenarios ◽  
Large Area ◽  
Gamma Ray Emission

AbstractThe Fermi Large Area Telescope (LAT) is the most sensitive instrument ever deployed in space for observing gamma-ray emission >100 MeV. This has also been demonstrated by its detection of quiescent gamma-ray emission from pions produced by cosmic-ray protons interacting in the solar atmosphere, and from cosmic-ray electron interactions with solar optical photons. The Fermi-LAT has also detected high-energy gamma-ray emission associated with GOES M-class and X-class solar flares, each accompanied by a coronal mass ejection and a solar energetic particle event, increasing the number of detected solar flares by almost a factor of 10 with respect to previous space observations. During the impulsive phase, gamma rays with energies up to several hundreds of MeV have been recorded by the LAT. Emission up to GeV energies lasting several hours after the flare has also been detected by the LAT. Of particular interest are the recent detections of three solar flares whose position behind the limb was confirmed by the STEREO satellites. While gamma-ray emission up to tens of MeV resulting from proton interactions has been detected before from occulted solar flares, the significance of these particular events lies in the fact that these are the first detections of >100 MeV gamma-ray emission from footpoint-occulted flares. We will present the Fermi-LAT, RHESSI and STEREO observations of these flares and discuss the various emission scenarios for these sources.

scholarly journals Observation of Seismic Effects of Solar Flares from the SOHO Michelson Doppler Imager

1998 ◽  
Vol 185 ◽  
pp. 191-194
Author(s):  
A.G. Kosovichev ◽  
V.V. Zharkova
Keyword(s):  
Solar Flares ◽  
Seismic Waves ◽  
Solar Surface ◽  
Active Regions ◽  
Impulsive Phase ◽  
High Energy ◽  
Solar Interior ◽  
Michelson Doppler Imager ◽  
Seismic Effects ◽  
Doppler Imager

Solar flares are the strongest localized seismic disturbances on the solar surface. During the impulsive phase a high-energy electron beam heats the chromosphere, resulting in explosive evaporation of chromospheric plasma at supersonic velocities. This upward motion is balanced by a downward recoil in the lower part of the chromosphere that excites propagating waves in the solar interior. On the solar surface the outgoing circular flare waves resemble ripples from a pebble thrown into a pond. We report on first observations of the seismic effects of a solar flare from the SOHO Michelson Doppler Imager (MDI) and compare the results with a theoretical model. Observation of flare seismic waves provide important information about the flare mechanism and about the subphotospheric structure of active regions.

scholarly journals High Energy Gamma-Ray Radiation Above 300 KeV Associated with Solar Activity

1975 ◽  
Vol 68 ◽  
pp. 341-359 ◽  
Author(s):  
E. L. Chupp ◽  
D. J. Forrest ◽  
A. N. Suri
Keyword(s):  
Experimental Data ◽  
Solar Flares ◽  
Gamma Ray ◽  
Impulsive Phase ◽  
Theoretical Work ◽  
High Energy ◽  
Energy Gamma ◽  
Charged Secondary ◽  
Rule Out ◽  
Made In

The present status of our knowledge concerning the production of gamma-ray lines and continuum during the impulsive phase of solar flares is reviewed. Our data in this field is based solely on the OSO-7 observations made in 1972, August 4 and August 7. The experimental data will be reviewed. These observations along with theoretical work of Ramaty and Lingenfelter (1973a, b) and the charged secondary observations of the Chicago group (Anglin et al., 1973) lead to the investigation of different hypothetical models to explain the production of neutral and charged secondaries in the solar atmosphere. At the present time it is not possible to rule out the preflare and postflare accumulation models if all the data is considered. We will discuss the outstanding experimental questions to be answered in future investigations.

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