WG3: Sep 2017 Event Analysis
Laura Hayes and Säm Krucker
In September 2017 the Sun showed an unexpectedly high level of activity this late in the solar cycle. A total of 4 GOES X-class flares occurred, including the most intense gamma-ray event of this cycle on 10 September, and many C- and M-class flares. These sets of observations are possibly the most valuable solar flare data of this solar cycle. Our working group will focus on measurements during this time period across the electromagnetic spectrum from radio frequencies through optical and UV to X-rays and gamma-rays, as well as in-situ particle measurements in the heliosphere and near-Earth environment. We kindly ask not to submit abstract involving other time periods. In addition to presentations by the working group participants, we will schedule a discussion session at the end on how to proceed with data analysis and interpretation.
|Properties of Coronal Hard X-ray Sources|
|Brian R. Dennis, Miguel A. Duval-Poo, Michela Piana, Anna Maria Massone, A. Gordon Emslie, Andrew R. Inglis, and Jingnan Guo||Talk|
|Results will be presented from a study of coronal hard X-ray sources in the X-class flare on 10 September 2017, in a similar event on 29 January 2005, and in other weaker flares. Both of the X flares have strong coronal hard X-ray sources to energies above 100 keV and gamma-ray emission above 100 MeV. The footpoint sources were largely over the limb for the 2017 event but not for the 2005 event, making it possible to determine the ratio of coronal-to-footpoint emission for the earlier event. The spatial extent of the coronal HXR sources have been determined for all events as a function of energy and time. These new results will be compared with the results for the same weaker events published by Veronig and Brown (2004) and Guo et al. (2012, 2013). In the weaker events, the coronal HXR source length was reported to increase with energy between 20 and 30 keV, suggestive of a nonthermal electron beam with the higher energy electrons traveling further in a dense coronal loop. These earlier results are being re-evaluated based on new analysis procedures.|
|The X9 SOL2017-09-06 event observed at submillimeter and mid-IR wavelengths|
|G. Giménez de Castro, J.-P. Raulin, J.F. Valle Silva, P.J.A. Simões, A.S. Kudaka, A. Valio||Talk|
|Active Region 12673 produced the most intense events of cycle 24: in a few days of early September 2017, four X-class and eight M-class
flares occurred. We observed SOL2017-09-06T12:00, a GOES X9.3 flare at submillimeter with the Solar Submillimeter Telescope (SST) focal array while making a solar map, at 30 THz with a mid- IR camera and with an Halpha telescope. In this work we compare the mid-IR with Halpha, RSTN micro-waves (MW) , GOES soft X-rays, and HMI white light (WL). The mid-IR source was not resolved by the camera, implying a size less or equal the diffraction limit (17\”). It starts in coincidence with Halpha and WL, minutes before 15.4 GHz, the three
wavelengths increase smoothly peaking simultaneously, and contrary to MW, they have less features. The decreasing phase are similar,
although the total duration is longer at mid-IR (~60 min) than at WL (~20 min). When the event started, the sun was at low elevation,
increasing the atmospheric absorption at submillimeter. Since the antenna was making raster scans, it is not easy to get a time profile.
Synthesized maps indicate a maximum flux of around 2000 sfu at 212 GHz, assuming a source of the same size as the WL, but not well
determined at 405 GHz.
A thermal origin for the mid-IR emission is suggested by the similarities between 30 THz and WL, although its long duration
challenges this interpretation.
|Long Duration Quasi-Periodic Pulsations Detected in the September 10 2017 X8.2 Flare|
|Laura A. Hayes, Peter T. Gallagher, Brian Dennis, Jack Ireland, Andrew Inglis, Diana Morosan||Talk|
|Solar flare emission often displays pulsating and oscillatory signatures in the emission, known as quasi-periodic pulsations (QPP). QPP are typically identified during the impulsive phase of flares, yet in some cases, their presence is detected late into the decay phase. Here we report extensive fine structure QPP that are detected in the large X8.2 flare from 10 September 2017. The flare configuration and long duration offers a unique view to study QPP signatures and their relation to the length of the flaring loop. The QPP are observed to persist upto four hours after the impulsive phase has ended. Focusing on the thermal pulsations observed in GOES/XRS and AIA 131A channel, we use a combination of wavelet and Fourier based techniques to analyze the timescale evolution of the pulsations during the decay phase of the flare. We relate the timescale of these long duration QPP to the Alfven speed and length scales using spatially resolved observations of RHESSI and AIA/SDO.|
|EVE spectroscopy of the September events|
|The EVE spectrometers observe the Sun spectroscopically in the EUV,
with no spatial resolution but with very high throughput and good
(10 s) temporal sampling. The Doppler measurements exceed most
others in precision but the interpretation has distinct \”Sun as a
star\” limitations. I will describe these limitations and give an
overview of the three main September events (SOL2017-09-04, -06,
and -10, GOES M5.5, X2.2, X8.2), all of which were captured by
MEGS-B (330-1066 A). The spectroscopy of SOL2017-09-10 is strikingly
different because of its limb occultation.
|Photospheric Fe I lines in Sep 6, 2017 X flare seen in emission by SOT/HINODE|
|Jana Kasparova, Jan Jurcak, Michal Svanda, Lucia Kleint, Petr Heinzel||Talk|
|During the X-class flare on Sep 6, 2017 Fe I lines were detected in emission by SOT/HINODE. We used SIR code to invert the observed Fe I Stokes profiles and determined photospheric structure affected by the flare heating. We also show that the lines are probably affected by continuum emission from higher atmospheric layers. Results are discussed in frame of relevant non-LTE RHD models.|
|Continuum emission and spectral line profiles during the Sep 6, 2017 flare|
|The Sep 6, 2017 flare showed an unusually high enhancement in continuum and spectral line emission. In a very rare observation, the Hinode spectrograph had its slit scanning across the flare kernels just at the right time, capturing both Fe I lines in emission. We analyze the occurrence of this spectral line emission both in Hinode/SP and in HMI and compare it to enhanced continuum emission, which reaches up to 300%. We use inversions to estimate the temperature structure of the atmosphere during the flare.|
|RHESSI observations of the 2017 September 10 flare|
|I will review the RHESSI observations of the September 10, 2017 flare.|
|The observation of 2017-09-09 M1.2 flare by the Expanded Owens Valley Solar Array and The Reuven Ramaty High Energy Solar Spectroscopic Imager|
|We present the observation of the near-limb M1.2 flare on 2017 September 9 successfully done by the newly commissioned Expanded Owens Valley Solar Array (EOVSA) and the The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). During its impulsive phase, this flare exhibited an interesting delayed response in microwave (MW) high frequency emission (peaking at ~22:50 UT) compared to the several hard X-ray (HXR) peaks starting from ~22:26 UT. The initial analysis shows at least one footpoint source that is co-spatial in HXR 25-50 keV and MW optically-thin frequency at ~22:50 UT, indicating the existence of nonthermal particle acceleration and precipitation to the chromosphere. The spatially-integrated spectrum at this time reveals a rather low peak frequency ~4 GHz, and the MW source is observed to be located at progressively higher altitude and occupying broader area. We interpret this result in the light of the large, high-altitude nonthermal particle population that have been discussed in recent studies.|
|Gamma-ray Emission during Impulsive Phase of the 2017-Sep-06 X9.3 Flare|
|Alexandra L. Lysenko, Sergey A. Anfinogentov, Gregory D. Fleishman||Talk|
|The minimum of solar cycle 24 in September, 2017 demonstrated two remarkable solar flares, the X9.3 flare on September, 6, and the X8.2 flare on September, 10, which were followed by a sustained gamma-ray emission observed by Fermi-LAT instrument during more than 10 hours at energies >100 MeV. While the second flare, X8.2, was well observed in microwave, HXR and gamma-ray ranges, observations of the impulsive phase of the first one, X9.3, are rather poor: the impulsive phase occurred during “nights” of both RHESSI and Fermi spacecraft.
In this study we analyze gamma-ray emission during impulsive phase of the 2017-Sep-06 X9.3 flare registered by Konus-Wind instrument, operating in the energy range 20 keV – 15 MeV and orbiting near Lagrange point L1. This phase lasted from 11:54 to 12:03 UT and demonstrated a few peaks in HXR range and gamma-ray emission at energies up to a few MeV. We performed spectral analysis of this flare in HXR and gamma-ray ranges using the Bayesian statistics to distinguish between contributions from relativistic electron and positron emission and emission in gamma-ray lines, for which accelerated ions are responsible. We revealed temporal evolution of different spectral parameters and estimated properties of the particles accelerated during the flare impulsive phase.
|On the observation of a classical loop-prominence system during the 2017 September 10 flare.|
|Juan Carlos Martinez, Sam Krucker, Pascal Saint-Hilaire||Talk|
|We report observations of white-light ejecta in the low corona after the 2017 September 10 flare, using data from the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory. We report the observation of a classical loop-prominence system, but are brighter than expected and possibly seen here in the continuum rather than line emission. We studied the spatial and temporal relation between RHESSI X-ray and the white-light emissions. We also studied the HMI spectroscopic data to determine the most probable emission mechanism that can explain the observation of the loop-prominence system.|
|Multiple Regions of Shock Accelerated Electron Beams in the Solar Corona|
|Diana E. Morosan, Laura A. Hayes, Sophie A. Murray, Eoin P. Carley, Pietro Zucca, Richard A. Fallows, Joe McCauley, Emilia Kilpua, Gottfried Mann, Christian Vocks, Peter T. Gallagher||Talk|
|The Sun is an active star that produces the most powerful explosions in the solar system in the form of solar flares, often accompanied by coronal mass ejections (CMEs) that drive colisionless shocks in the corona. CME shocks are efficient particle accelerators and shock signatures associated with CMEs are often observed as solar radio bursts. However, the relationship between radio shock signatures on the Sun and the expansion of a CME is still not well understood due to previous limitations of low radio frequency imaging (<150 MHz) where the most dramatic acceleration is believed to occur. Here, we exploit a unique set of observations from the Low Frequency Array (LOFAR) of a X8.2-class solar flare on 10 September 2017 and its associated very fast CME (3000 km/s). In particular, we image for the first time a multitude of radio shock signatures called herringbones. Using multi-wavelength analysis, we provide convincing evidence for shock accelerated electrons at multiple locations on the expanding CME flank.|
|Multi-methods analysis of the september 2017 events|
|Michele Piana, Miguel Duval Poo, Anna Maria Massone||Talk|
|We present here an analysis of the X class events occurred in September 2017, relying on the application of several inversion methods against hard X-ray visibilities provided by RHESSI. Specific focus will be given to the performances of a recently introduced wavelet-based method for compressed sensing. Comments on corresponding SDO/AIA EUV images and RHESSI gamma-ray spectra will be possibly discussed|
|Understanding the HMI pseudocontinuum Ic in white-light solar flares|
|M. Švanda, J. Jurčák, J. Kašparová, L. Kleint||Talk|
|The utilisation of HMI intensitygrams to study white-light solar flares was suggested in several papers recently. We use a unique opportunity of 6-Sep-2017 X9.3 flare to compare various data products from HMI and Hinode to learn about the reliability of HMI data products. We show that the use of Ic intensitygrams is justified when searching for white-light flares kernels, however it cannot be used for any kind of photometric or energetic studies.|