Correlation between hard and soft X-ray bursts and small-scale acceleration processes during the rise phase of solar flares

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.

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Interferometry of Solar Flares at 3-mm Wavelength

Symposium - International Astronomical Union ◽

10.1017/s0074180900124350 ◽

1994 ◽

Vol 154 ◽

pp. 131-135

Author(s):

M. R. Kundu ◽

S. M. White ◽

N. Gopalswamy ◽

J. Lim

Keyword(s):

Particle Acceleration ◽

Solar Flares ◽

Acceleration Process ◽

X Ray ◽

Steep Rise ◽

Show Evidence ◽

Rise Phase

We describe a set of millimeter interferometric observations of solar flares carried out in conjunction with GRO experiments during the 1991 June Campaign of the Max'91 Program. We show evidence that millimeter emission probes the most energetic (MeV) electrons in solar flares; we also find that in the same flare there can be both impulsive nonthermal and gradual thermal millimeter emission. Millimeter emission usually occurs at the steep rise phase of the hard X-ray emitting electrons (25-100 KeV). There appears to exist some delay between BIMA mm-emission onset and GRO-BATSE 25-100 KeV X-ray emission. Both results have implications for the particle acceleration process.

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Plasma heating in the initial phase of solar flares

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309992791 ◽

2009 ◽

Vol 5 (S264) ◽

pp. 282-284

Author(s):

P. Rudawy ◽

M. Siarkowski ◽

R. Falewicz

Keyword(s):

Solar Flares ◽

Energy Transport ◽

Electron Beams ◽

Plasma Heating ◽

Impulsive Phase ◽

Thermal Electron ◽

Flare Loop ◽

X Ray ◽

Heating Source ◽

Rise Phase

AbstractIn this paper we analyze soft and hard X-ray emission of the 2002 September 20 M1.8 GOES class solar flare observed by RHESSI and GOES satellites, where soft X-ray emission precedes the onset of the main bulk hard X-ray emission by ~5 min. This suggests that an additional heating mechanism may be at work at the early beginning of the flare. However RHESSI spectra indicate presence of the non-thermal electrons also before impulsive phase. So, we assumed that a dominant energy transport mechanism during rise phase of solar flares is electron beam-driven evaporation. We used non-thermal electron beams derived from RHESSI spectra as the heating source in a hydrodynamic model of the analyzed flare. We showed that energy delivered by non-thermal electron beams is sufficient to heat the flare loop to temperatures in which it emits soft X-ray closely following the GOES 1–8 Å light-curve.

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The occurrence of single hard x-ray sources in solar flares

Advances in Space Research ◽

10.1016/s0273-1177(03)90419-4 ◽

2003 ◽

Vol 32 (12) ◽

pp. 2483-2488

Author(s):

C GOFF ◽

S MATTHEWS ◽

L HARRA

Keyword(s):

Solar Flares ◽

X Ray

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QPOs in compact binaries from small scale eruptions in an inner magnetized disk

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3410 ◽

2020 ◽

Author(s):

Nicolas Scepi ◽

Mitchell C Begelman ◽

Jason Dexter

Keyword(s):

Rapid Heating ◽

Small Scale ◽

Type B ◽

Periodic Oscillations ◽

X Ray ◽

Compact Binaries ◽

Heating And Cooling ◽

Low Mass ◽

X Ray Binaries ◽

Standard Disk

Abstract Dwarf novæ (DNe) and low mass X-ray binaries (LMXBs) are compact binaries showing variability on time scales from years to less than seconds. Here, we focus on explaining part of the rapid fluctuations in DNe, following the framework of recent studies on the monthly eruptions of DNe that use a hybrid disk composed of an outer standard disk and an inner magnetized disk. We show that the ionization instability, that is responsible for the monthly eruptions of DNe, is also able to operate in the inner magnetized disk. Given the low density and the fast accretion time scale of the inner magnetized disk, the ionization instability generates small, rapid heating and cooling fronts propagating back and forth in the inner disk. This leads to quasi-periodic oscillations (QPOs) with a period of the order of 1000 s. A strong prediction of our model is that these QPOs can only develop in quiescence or at the beginning/end of an outburst. We propose that these rapid fluctuations might explain a subclass of already observed QPOs in DNe as well as a, still to observe, subclass of QPOs in LMXBs. We also extrapolate to the possibility that the radiation pressure instability might be related to Type B QPOs in LMXBs.

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Non-Invasive Technical Investigation of English Portrait Miniatures Attributed to Nicholas Hilliard and Isaac Oliver

Heritage ◽

10.3390/heritage4030064 ◽

2021 ◽

Vol 4 (3) ◽

pp. 1165-1181

Author(s):

Flavia Fiorillo ◽

Lucia Burgio ◽

Christine Slottved Kimbriel ◽

Paola Ricciardi

Keyword(s):

Fluorescence Spectroscopy ◽

Scientific Methodology ◽

Small Scale ◽

Artistic Practice ◽

X Ray ◽

Non Invasive ◽

Miniature Painting ◽

Entire Career ◽

Similarities And Differences ◽

Victoria And Albert Museum

This study presents the results of the technical investigation carried out on several English portrait miniatures painted in the 16th and 17th century by Nicholas Hilliard and Isaac Oliver, two of the most famous limners working at the Tudor and Stuart courts. The 23 objects chosen for the analysis, spanning almost the entire career of the two artists, belong to the collections of the Victoria and Albert Museum (London) and the Fitzwilliam Museum (Cambridge). A non-invasive scientific methodology, comprising of stereo and optical microscopies, Raman microscopy, and X-ray fluorescence spectroscopy, was required for the investigation of these small-scale and fragile objects. The palettes and working techniques of the two artists were characterised, focusing in particular on the examination of flesh tones, mouths, and eyes. These findings were also compared to the information written in the treatises on miniature painting circulating during the artists’ lifetime. By identifying the materials and techniques most widely employed by the two artists, this study provides information about similarities and differences in their working methods, which can help to understand their artistic practice as well as contribute to matters of attribution.

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