QSEBs with Co-spatial IRIS Bursts

Nelson, C. J., Reid, A.,

Oliver, R., Mathioudakis, M., Erdélyi, R.

Nabil Freij

Contents

Part 1

Part 2

Conclusions

  • Ellerman Bombs (EBs)
  • Identification of EBs
  • Properties of EBs
  • IRIS Bursts (IBs)
  • Quiet-Sun EBs (QSEBs)
  • Our QSEBS
  • QSEBs and IBs
  • Line Synthesis

Part 1

Ellerman Bombs

and

IRIS Bursts

Ellerman Bombs (EBs)

Ellerman in 1917 found and labelled EBs as, solar hydrogen bombs.

 

Reported on by Mitchel in 1909, Severny in 1956 and Lyct in 1944.

 

The small size of these events made them difficult to study.

Ellerman, F. 1917, ApJ, 46, 298

Ellerman Bombs (EBs)

2012 SST Hα linescan

Basic EB signature:

Enhanced emission in the line wings of  Hα.

Unlike in Ellerman's time, we can now resolve EBs with extreme detail.

Identification of EBs

How do we make sure these are all EBs and not other features?

All these bright events are not likely to just be EBs. 

SST Hα +0.1 nm

SST Hα -0.1 nm

Identification of EBs

Earlier research into EBs looked for:

  • Regions of enhanced brightness in and around ARs.
    • Generally ~130-150% of the background intensity.
  • Filtered out regions that do not temporal overlap.

 

However, the intensity limit alone was considered insufficient. Pseudo-EBs and other features had been mislabeled as EBs.

  • Substantial brightening of the extended wings of Hα.
    • ​Wing intensity decreases as you move along the line profile.
  • Wing brightenings exceed those from other similar brightening events.
  • No Hα core brightening. 
  • If spatial resolution and angle allow: flame-like morphology. 
  • EBs should be visible in SDO/AIA 160 mn or 170 nm imaging.

Properties of EBs

EBs are extremely dynamic events:

  • Lifespan under 10 minutes.
  • The lengths and widths of EBs are around 1".
  • Their behaviour is usually described as 'flame-like'.
  • On occasion, they are repetitive.
  • Occur exclusively within Active Regions (ARs).

EBs also have signatures in other wavelengths:

  • Ca II 854.2 nm line wings intensity increase.
  • SDO/AIA 160 nm and 170 nm intensity increase.

EBs are known now to be strong-field opposite-polarity magnetic cancellations.

IRIS Bursts (IBs)

First reported by Peter et. al., (2014) using Interface Region Imaging Spectrograph (IRIS).

IBs are very intense, short-lived, small-scale brightness seen in IRIS UV lines.

Peter et. al., (2014)

IRIS Bursts (IBs)

Large increases in Si IV intensity indicates extremely hot plasma.

Absorption lines suggest that the hot material originates from the photosphere.

Tian et. al., (2016) shows a strong link between IBs and EBs.

Peter et. al., (2014)

Part 2

Quiet-Sun Ellerman Bombs (QSEBs)

Background

First discovered by Rouppe van der Voort et. al., (2016) using a large back catalogue of SST data.

Similar to EBs but are smaller, less intense events that occur in quiet areas of the solar surface.

Rouppe van der Voort, et al., A&A, 592 (2016) A100

Known Properties

Length: <0.5 arcsec, Width: <0.25 arcsec, Lifetime: <1 minute

 

No brightening of wings in Ca II 854.2 nm.

No brightening of AIA 160 nm or 170 nm.

No brightening in IRIS UV slit-jaw images.

 

This makes them harder to distinguish from pseudo-EBs or other features.

Observations

SST/CRISP from 9th June 2016.

 

Pointing (-900”, -100”) at a quiet Sun region, located at the foot-points of an
apparent loop system.

 

21-point Hα line scan (±0.2 nm).

21-point Ca II 854.2 nm (±0.2 nm).

 

Cadence ~ 27 seconds.

Observations

IRIS was co-observing rastering over a large FOV, sampling from off-limb to on-disk.

320-step dense rasters with slit-jaw imager data:

140 nm (18.6 s), 279.6 nm (18.6 s), and 283.2 nm (91 s) filters.

Identification of QSEBs

In order to identify QSEBS, we locate regions that follow these rules:

  • Intense brightness (>130% of local background intensity) at the wings only.
  • Short-lived (1<lifetime<15 minute).
  • Small-scale (<2").

Then:

  • Check line profiles are consistent with QS/EB-like events.
  • Apparent explosive behaviour was required.

This results in 21 QSEBs within this dataset.

Identification of QSEBs

Agreement with Rouppe van der Voort et al., A&A (2016) - no signature is found in Ca II 854.2 nm line profiles

Properties of QSEBs

Average Lengths ~ 0.6”

Average Widths ~ 0.4”
Average Lifetimes ~120 s

🞣 - EBs

- QSEBs

Our results are overall, consistent with Rouppe van der Voort et al., (2016).

 

Expect for lifetimes. With the most likely reason our slow cadence.

Properties of QSEBs

We have 3 examples of QSEBs repeating in a similar manner to EBs.

Initial event

Hα

blue

wing

line

core

red

wing

Repetition

Properties of QSEBs

Unlike Rouppe van der Voort et. al., (2016), we have some SDO/AIA 160 nm brightening with no signatures in SDO/AIA 170 nm.

Links Between QSEBs and IBs

6 QSEBs overlap with the IRIS co-observation.

2 compact brightenings in the IRIS SJI 140.0 nm filter.

Links Between QSEBs and IBs

QSEB (f) was sampled by the IRIS slit. 

Si IV 139.3 nm

Si IV 140.3 nm

Increased intensity in Si IV 139.3 nm and 140.3 nm lines.

Wing intensity increases in C II and Mg II.

 

Consistent with IBs seen by Peter et al., (2014), Vissers et al., (2015) and Tian et al., (2016).

C II

Mg II

Line Synthesis

In order to further understand QSEBs, we attempted to model their Hα and Ca II 854.2 nm signatures.

Rouppe van der Voort et. al., (2016) suggested that QSEBs form where they only affect Hα and not Ca II 854.2 nm.

The basis for this work usings Reid et. al., (2017) models, utilizing the 1D RADYN code.

  1. Take a background quiet Sun atmosphere for temperature, density and composition.
  2. Perturb the atmosphere at a specific height range by artificially adding energy, modelling the reconnection event.
  3. Allow the atmosphere to settle for 10 seconds.
  4. Use radiative transfer methods to reproduce Hα and Ca II 854.2 nm line profiles.

Line Synthesis

But we could find the opposite.

No matter where we input the energy into the solar atmosphere. We always increase both the Hα and Ca II 854.2 nm line wings.

Conclusions

Some QSEBs appear to be linked to IRIS Bursts.

This implies that energetic magnetic reconnection can occur throughout the quiet-Sun.

 

Some repetition is observed suggesting that QSEBs could form at specific locations.

Further observations required to identify and understand what makes these locations special.

 

Our modelling attempts were unsuccessful in fitting the Hα and Ca II 854.2 nm line profiles.

This indicates that the position of energy deposition within the solar atmosphere cannot suppress the increased emission expected in the Ca II 854.2 nm line wings.

Conclusions

Thank you, any questions?

QSEBs and IBs

By Nabil Freij

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