Spectral Evidence for Heating at Large Column Mass in Umbral Solar Flare Kernels I: IRIS NUV Spectra of the X1 Solar Flare of 2014 Oct 25

Abstract

The GOES X1 flare SOL2014-10-25T17:08:00 was a three-ribbon solar flare observed with IRIS in the near and far ultraviolet. One of the flare ribbons crossed a sunspot umbra, producing a dramatic, $\sim 1000$% increase in the near-ultraviolet (NUV) continuum radiation. We comprehensively analyze the ultraviolet spectral data of the umbral flare brightenings, which provide new challenges for radiative-hydrodynamic modeling of the chromospheric velocity field and the white-light continuum radiation. The emission line profiles in the umbral flare brightenings exhibit redshifts and profile asymmetries, but these are significantly smaller than in another, well-studied X-class solar flare. We present a ratio of the NUV continuum intensity to the Fe II 2814.45 Ang intensity. This continuum-to-line ratio is a new spectral diagnostic of significant heating at high column mass (log $m/$[g cm${}^{-2}]>-2$) during solar flares because the continuum and emission line radiation originate from relatively similar temperatures but moderately different optical depths. The full spectral readout of these IRIS data also allow for a comprehensive survey of the flaring NUV landscape: in addition to many lines of Fe II and Cr II, we identify a new solar flare emission line, He I $\lambda 2829.91$ (as previously identified in laboratory and early-type stellar spectra). The Fermi/GBM hard X-ray data provide inputs to radiative-hydrodynamic models (which will be presented in Paper II) in order to better understand the large continuum-to-line ratios, the origin of the white-light continuum radiation, and the role of electron beam heating in the low atmosphere.

arXiv comment19 pg, 10 fig, 2 appendices. Accepted for publication in ApJ

References in corpus (49)

• The Fermi Gamma-Ray Burst Monitor
• The Interface Region Imaging Spectrograph (IRIS)
• The Photometric Performance and Calibration of the HST Advanced Camera For Surveys
• Radiative Hydrodynamic Models of the Optical and Ultraviolet Emission from Solar Flares
• Time-Resolved Properties and Global Trends in dMe Flares from Simultaneous Photometry and Spectra
• A Unified Computational Model for Solar and Stellar Flares
• Magnetic Field Structures Triggering Solar Flares and Coronal Mass Ejections
• Extreme ultraviolet frequency comb metrology
• The Confined X-class Flares of Solar Active Region 2192
• Temporal evolution of chromospheric evaporation: case studies of the M1.1 flare on 2014 September 6 and X1.6 flare on 2014 September 10
• Radiative Hydrodynamic Models of Optical and Ultraviolet Emission from M Dwarf Flares
• Compton backscattered and primary X-rays from solar flares: angle dependent Green's function correction for photospheric albedo
• The Radiated Energy Budget of Chromospheric Plasma in a Major Solar Flare Deduced From Multi-Wavelength Observations
• Continuum Enhancements in the Ultraviolet, the Visible and the Infrared during the X1 flare on 2014 March 29
• The height of a white-light flare and its hard X-ray sources
• The Atmospheric Response to High Nonthermal Electron Beam Fluxes in Solar Flares I: Modeling the Brightest NUV Footpoints in the X1 Solar Flare of 2014 March 29
• New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation
• Simulations of the Mg II k and Ca II 8542 lines from an Alfvén Wave-heated flare chromosphere
• On the origin of 3 seismic sources in the proton-rich flare of October 28, 2003
• Propagation of Alfvénic Waves From Corona to Chromosphere and Consequences for Solar Flares
• Data-driven Radiative Hydrodynamic Modeling of the 2014 March 29 X1.0 Solar Flare
• Hydrogen Balmer Continuum in Solar Flares Detected by the Interface Region Imaging Spectrograph (IRIS)
• M Dwarf Flare Continuum Variations on One-Second Timescales: Calibrating and Modeling of ULTRACAM Flare Color Indices
• Hydrogen Balmer Line Broadening in Solar and Stellar Flares
• Alfvénic Wave Heating of the Upper Chromosphere in Flares
• Detailed and simplified non-equilibrium helium ionization in the solar atmosphere
• The spectrum of Fe II
• The formation of IRIS diagnostics V. A quintessential model atom of C II and general formation properties of the C II lines at 133.5 nm
• A Very Bright, Very Hot, and Very Long Flaring Event from the M Dwarf Binary System DG CVn
• IRIS Observations of the Mg II h & k Lines During a Solar Flare
• The Near-Ultraviolet Continuum Radiation in the Impulsive Phase of HF/GF-Type dMe Flares I: Data
• Fine structure of flare ribbons and evolution of electric currents
• The Power-Law Distribution of Flare Kernels and Fractal Current Sheets in a Solar Flare
• Kepler Flares IV: A Comprehensive Analysis of the Activity of the dM4e Star GJ 1243
• Parameterizations of Chromospheric Condensations in dG and dMe Model Flare Atmospheres
• A Hydrodynamic Model of Alfvénic Wave Heating in a Coronal Loop and its Chromospheric Footpoints
• On the nature of off-limb flare continuum sources detected by SDO/HMI
• Height structure of X-ray, EUV and white-light emission in a solar flare
• Spectral and Imaging Observations of a White-light Flare in the Mid-Infrared
• Structure and Stability of Magnetic Fields in Solar Active Region12192 Based on Nonlinear Force-Free Field Modeling
• Characteristics that Produce White-Light Enhancements in Solar Flares Observed by Hinode/SOT
• Reproducing Type II White-Light Solar Flare Observations with Electron and Proton Beam Simulations
• Triggering Process of the X1.0 Three-ribbon Flare in the Great Active Region NOAA 12192
• Optical Spectral Observations of a Flickering White-Light Kernel in a C1 Solar Flare
• The Multiple Continuum Components in the White Light Flare of 16 January 2009 on the dM4.5e Star YZ CMi
• On the origin of the flare emission in IRIS' SJI 2832 filter: Balmer continuum or spectral lines?
• Relationship between chromospheric evaporation and magnetic field topology in M-class solar flare
• Suppression of Hydrogen Emission in an X-class White-light Solar Flare
• Solar jet-like features rooted in flare ribbons

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