Constraining Solar Flare Differential Emission Measures with EVE and RHESSI

Deriving a well-constrained differential emission measure (DEM) distribution for solar flares has historically been difficult, primarily because no single instrument is sensitive to the full range of coronal temperatures observed in flares, from 2 to 50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory with X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first time, a self-consistent, well-constrained DEM for jointly observed solar flares. EVE is sensitive to ~2-25 MK thermal plasma emission, and RHESSI to 10 MK; together, the two instruments cover the full range of flare coronal plasma temperatures. We have validated the new technique on artificial test data, and apply it to two X-class flares from solar cycle 24 to determine the flare DEM and its temporal evolution; the constraints on the thermal emission derived from the EVE data also constrain the low energy cutoff of the non-thermal electrons, a crucial parameter for flare energetics. The DEM analysis can also be used to predict the soft X-ray flux in the poorly observed ~0.4-5 nm range, with important applications for geospace science.

[1]  C. Jordan.  Ionization Equilibria for High Ions of Fe and Ni , 1970 .

[2]  John C. Brown,et al.  The deduction of energy spectra of non-thermal electrons in flares from the observed dynamic spectra of hard X-ray bursts , 1971 .

[3]  J. Cook,et al.  The decay of the 1973 August 9 flare. , 1979 .

[4]  Kevin C. Hurley,et al.  A new component of hard X-rays in solar flares , 1981 .

[5]  J. Lemen,et al.  Intercomparison of flare observations with two SMM spectrometers: BCS and HXIS , 1988 .

[6]  S. Bowyer,et al.  Extreme Ultraviolet Astronomy , 1991 .

[7]  Howard A. Garcia,et al.  Temperature and emission measure from goes soft X-ray measurements , 1994 .

[8]  W. E. Behring,et al.  Electron Temperature, Emission Measure, and X-Ray Flux in A2 to X2 X-Ray Class Solar Flares , 1996 .

[9]  H. Mason,et al.  CHIANTI - an atomic database for emission lines - I. Wavelengths greater than 50 Å , 1997 .

[10]  P. Mazzotta,et al.  Ionization Balance for Optically Thin Plasmas: Rate Coefficients for all Atoms and Ions of the Elements H to Ni and implication for the calculated X-ray spectrum , 1998, astro-ph/9806391.

[11]  Alphonse C. Sterling,et al.  Observational Plasma Astrophysics: Five Years of Yohkoh and Beyond , 1998 .

[12]  J. McTiernan,et al.  The Solar Flare Soft X-Ray Differential Emission Measure and the Neupert Effect at Different Temperatures , 1999 .

[13]  D. A. Landis,et al.  The RHESSI Spectrometer , 2002 .

[14]  J. Brown,et al.  Nonsolar astronomy with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) , 2003, SPIE Astronomical Telescopes + Instrumentation.

[15]  Stellar Coronal Astronomy , 2003, astro-ph/0302565.

[16]  Gordon D. Holman,et al.  Electron Bremsstrahlung Hard X-Ray Spectra, Electron Distributions, and Energetics in the 2002 July 23 Solar Flare , 2003 .

[17]  K. Phillips,et al.  The Solar Flare 3.8-10 keV X-Ray Spectrum , 2004 .

[18]  S. White,et al.  Updated Expressions for Determining Temperatures and Emission Measures from Goes Soft X-Ray Measurements , 2005 .

[19]  B. Dennis,et al.  RHESSI Observations of the Solar Flare Iron-Line Feature at 6.7 keV , 2006, astro-ph/0607309.

[20]  Harry P. Warren,et al.  Soft X‐ray irradiances during solar flares observed by TIMED‐SEE , 2006 .

[21]  H. Mason,et al.  A benchmark study for CHIANTI based on RESIK solar flare spectra , 2007 .

[22]  Karen Willcox,et al.  Kinetics and kinematics for translational motions in microgravity during parabolic flight. , 2009, Aviation, space, and environmental medicine.

[23]  Manuel Güdel,et al.  X-ray spectroscopy of stars , 2009, 0904.3078.

[24]  F. G. Eparvier,et al.  Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO): Overview of Science Objectives, Instrument Design, Data Products, and Model Developments , 2010 .

[25]  J. Qiu,et al.  A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with Thermal Loop-top X-ray Source , 2010, 1106.3572.

[26]  A. Caspi,et al.  RHESSI LINE AND CONTINUUM OBSERVATIONS OF SUPER-HOT FLARE PLASMA , 2010, 1105.2839.

[27]  Sam Krucker,et al.  STATISTICAL PROPERTIES OF SUPER-HOT SOLAR FLARES , 2011 .

[28]  M. Aschwanden,et al.  Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares , 2011, 1109.6496.

[29]  J. Raulin,et al.  Origin of the Submillimeter Radio Emission During the Time-Extended Phase of a Solar Flare , 2011, 1109.5729.

[30]  D. Longcope,et al.  A MODEL FOR THE ORIGIN OF HIGH DENSITY IN LOOPTOP X-RAY SOURCES , 2011, 1107.2441.

[31]  M. Temmer,et al.  An Observational Overview of Solar Flares , 2011, 1109.5932.

[32]  Donald L. Woodraska,et al.  Extreme Ultraviolet Variability Experiment (EVE) Multiple EUV Grating Spectrographs (MEGS): Radiometric Calibrations and Results , 2012 .

[33]  W. Pesnell,et al.  The Solar Dynamics Observatory (SDO) , 2012 .

[34]  A. Oreshina,et al.  Perspectives of current-layer diagnostics in solar flares , 2013, 1404.4434.

[35]  H. Mason,et al.  CHIANTI—AN ATOMIC DATABASE FOR EMISSION LINES. XIII. SOFT X-RAY IMPROVEMENTS AND OTHER CHANGES , 2013 .

[36]  J. Qiu,et al.  DETERMINING HEATING RATES IN RECONNECTION FORMED FLARE LOOPS OF THE M8.0 FLARE ON 2005 MAY 13 , 2013, 1304.4521.

[37]  H. Warren,et al.  OBSERVATIONS OF THERMAL FLARE PLASMA WITH THE EUV VARIABILITY EXPERIMENT , 2012, 1211.1875.

[38]  Robert W. Schunk,et al.  Modeling the ionospheric E and F1 regions: Using SDO‐EVE observations as the solar irradiance driver , 2013 .

[39]  M. Aschwanden,et al.  The Compatibility of Flare Temperatures Observed with AIA, GOES, and RHESSI , 2014, 1401.4098.

[40]  T. Woods,et al.  Mechanisms and Observations of Coronal Dimming for the 2010 August 7 Event , 2014, 1404.1364.