Soft X-ray Fluxes of Major Flares Far Behind the Limb as Estimated Using STEREO EUV Images

Abstract

With increasing solar activity since 2010, many flares from the backside of the Sun have been observed by the Extreme Ultraviolet Imager (EUVI) on either of the twin STEREO spacecraft. Our objective is to estimate their X-ray peak fluxes from EUVI data by finding a relation of the EUVI with GOES X-ray fluxes. Because of the presence of the Fe xxiv line at 192 A, the response of the EUVI 195 A channel has a secondary broad peak around 15 MK, and its fluxes closely trace X-ray fluxes during the rise phase of flares. If the flare plasma is isothermal, the EUVI flux should be directly proportional to the GOES flux. In reality, the multithermal nature of the flare and other factors complicate the estimation of the X-ray fluxes from EUVI observations. We discuss the uncer- tainties, by comparing GOES fluxes with the high cadence EUV data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We conclude that the EUVI 195 A data can provide estimates of the X-ray peak fluxes of intense flares (e.g., above M4 in the GOES scale) with uncertainties of a factor of a few. Lastly we show examples of intense flares from regions far behind the limb, some of which show eruptive signatures in AIA images.

15 pages, 9 figures, accepted by Solar Physics

References in corpus (1)

• The Thermal Properties of Solar Flares Over Three Solar Cycles Using GOES X-ray Observations

Cited by in corpus (16)

• Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections
• Interplanetary Propagation Behavior of the Fast Coronal Mass Ejection from 23 July 2012
• Fermi-LAT Observations of High-energy Behind-the-limb Solar Flares
• First detection of >100 MeV gamma rays associated with a behind-the-limb solar flare
• The First Fermi-LAT Solar Flare Catalog
• Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles
• Comparing Long-Duration Gamma-Ray Flares and High-Energy Solar Energetic Particles
• First High-resolution Spectroscopic Observations of an Erupting Prominence Within a Coronal Mass Ejection by the Interface Region Imaging Spectrograph (IRIS)
• The unusual widespread solar energetic particle event on 2013 August 19. Solar origin and particle longitudinal distribution
• The Relation Between Large-Scale Coronal Propagating Fronts and Type II Radio Bursts
• Source of Energetic Protons in the 2014 September 1 Sustained Gamma-ray Emission Event
• Comment on "Detection and characterization of 0.5-8 MeV neutrons near Mercury: Evidence for a solar origin"
• Evidence of Significant Energy Input in the Late Phase of a Solar Flare from NuSTAR X-Ray Observations
• Global Energetics of Solar Flares. XI. Flare Magnitude Predictions of the GOES-Class
• Multiwavelength Stereoscopic Observation of the May 1, 2013 Solar Flare and CME
• GOES class estimation for behind-the-limb solar flares using MESSENGER SAX