Self-absorption in the solar transition region

Abstract

Transient brightenings in the transition region of the Sun have been studied for decades and are usually related to magnetic reconnection. Recently, absorption features due to chromospheric lines have been identified in transition region emission lines raising the question of the thermal stratification during such reconnection events. We analyse data from the Interface Region Imaging Spectrograph (IRIS) in an emerging active region. Here the spectral profiles show clear self-absorption features in the transition region lines of Si\,{\sc{iv}}. While some indications existed that opacity effects might play some role in strong transition region lines, self-absorption has not been observed before. We show why previous instruments could not observe such self-absorption features, and discuss some implications of this observation for the corresponding structure of reconnection events in the atmosphere. Based on this we speculate that a range of phenomena, such as explosive events, blinkers or Ellerman bombs, are just different aspects of the same reconnection event occurring at different heights in the atmosphere.

Accepted for publication in ApJ

References in corpus (7)

• The Interface Region Imaging Spectrograph (IRIS)
• Hot Explosions in the Cool Atmosphere of the Sun
• Prevalence of Small-scale Jets from the Networks of the Solar Transition Region and Chromosphere
• Spectroscopic evidence for helicity in explosive events
• Conversion from mutual helicity to self-helicity observed with IRIS
• Explosive events - swirling transition region jets
• Molecular absorption in transition region spectral lines

Cited by in corpus (26)

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• Magnetic reconnection at the earliest stage of solar flux emergence
• The development of lower-atmosphere turbulence early in a solar flare
• Non-Maxwellian analysis of the transition-region line profiles observed by the Interface Region Imaging Spectrograph
• IRIS Burst Spectra Co-Spatial To A Quiet-Sun Ellerman-Like Brightening
• A Si IV/O IV electron density diagnostic for the analysis of IRIS solar spectra
• Multi thermal atmosphere of a mini solar flare during magnetic reconnection observed with IRIS
• Solar Ultraviolet Bursts in a Coordinated Observation of IRIS, Hinode and SDO
• Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite
• Occurrence and Statistics of IRIS Bursts
• Macrospicules and Their Connection to Magnetic Reconnection in the Lower Atmosphere
• Diagnosing the Optically Thick/Thin Features Using the Intensity Ratio of Si IV Resonance Lines in Solar Flares
• Plasma injection into a solar coronal loop
• Non-equilibrium ionization by a periodic electron beam II. Synthetic Si IV and O IV transition region spectra
• Synthetic IRIS spectra of the solar transition region: Effect of high-energy tails
• Evidence for two-loop interaction from IRIS and SDO observations of penumbral brightenings
• Spectroscopic Observations of High-speed Downflows in a C1.7 Solar Flare
• Flows and magnetic field structures in reconnection regions of simulations of the solar atmosphere: do flux pile-up models work?
• Chromospheric UV bursts and turbulent driven magnetic reconnection
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• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)
• Variation in the intensity ratio at each wavelength point of the Si iv 1394/1403 Å lines. Spectral diagnostics of a bifurcated eruption
• On the ratios of \ion{Si}{4} lines ($\lambda$1394/$\lambda$1403) in an emerging flux region