High cadence IRIS observations of evaporating flare ribbon sources

David Graham, Gianna Cauzzi, Luca Zangrilli INAF - Osservatorio Astrofisico di Arcetri

September 10th 2014

• X1.6 17:45 UT

• Sit and stare - 9.4 second cadence

• Coronal + chromospheric temperature lines

• Fe XXI + Mg II

• 0.33’’ x 0.167’’ pixel size

1400Å Slitjaw Image (Si IV)Ribbon dynamics and characteristics

• Every slit pixel shows a unique and complete flare evolution (81 flares for the price of 1!)

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17:26:01

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17:30:42

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17:33:50

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17:37:55

1400Å Slitjaw

SPEX FERMI GBM Count Flux vs Time

17:30 17:45 18:00 18:15Start Time (10-Sep-14 17:15:00)

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Detectors: NAI_024.6 to 15.2 keV (Data with Bk)15.2 to 24.3 keV (Data with Bk)24.3 to 50.9 keV (Data with Bk)50.9 to 98.8 keV (Data with Bk)98.8 to 296.4 keV (Data with Bk)296.4 to 601.2 keV (Data with Bk)601.2 to 2000.0 keV (Data with Bk)

14-May-2015 13:17

Fe XXIC II

Constrained Si II (from Fe XII window)

Fe XXI Window - Fitting example

Fe II tied centroids

1352.5 1353.0 1353.5 1354.0 1354.5Wavelength (Å)

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Si II Fe II Fe II C IH2 Si II

Mg II (2791.55 Subordinate line) – Bisector analysis (Ding et al. 1995)

Use the 30% bisector for analysis - maximum shift without including background or unknown blends

Fe XXI fitted (green) - 1354.1 rest wavelength

1352.5 1353.0 1353.5 1354.0 1354.5Wavelength (Å)

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17:29:58

1352.5 1353.0 1353.5 1354.0 1354.5Wavelength (Å)

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17:30:45

1352.5 1353.0 1353.5 1354.0 1354.5Wavelength (Å)

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17:33:52

1352.5 1353.0 1353.5 1354.0 1354.5Wavelength (Å)

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17:37:47

2791.2 2791.4 2791.6 2791.8 2792.0Wavelength (A)

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2791.2 2791.4 2791.6 2791.8 2792.0Wavelength (A)

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2791.2 2791.4 2791.6 2791.8 2792.0Wavelength (A)

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2791.2 2791.4 2791.6 2791.8 2792.0Wavelength (A)

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• Section of 81 pixels

• Ribbon moves along slit at a constant rate

• Co-spatial Mg II intensity and condensation flows

• Mg II and Fe XXI flows co-spatial (?)

• Apparent delay in Fe XXI flows (~65s)

Mg II 15 & 30 km/s

Fe XXI >270 (yellow), >200 (dark blue), >100 (blue) km/s

17:26 17:28 17:30 17:32 17:34Start Time (10-Sep-14 17:25:11)

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17:26 17:28 17:30 17:32 17:34Start Time (10-Sep-14 17:25:11)

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• Superposed epoch analysis of all pixels (colour maximum 20 instances)

• Remarkable curves for 81 flaring pixels

• Evaporation duration ~ 500 seconds / Condensation ~ 60 seconds. (Fisher 1986 model)

• Previous observed condensation time ~ 2-3 minutes (Ichimoto & Kurokawa 1984, Ding 1995 et al.)

0 240 480 720 960Time (s)

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Fe XXI Velocity

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Mg II Velocity (30% bisector)

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• Velocity profile - good proxy for energy deposition in the chromosphere (Fisher 1986/89)

• Average temporal profile + average spatial profile

• Upper limit to the size - 1.5” (includes ribbon inclination and movement)

• Ribbon’s apparent motion ~0.025”/s

0 10 20 30 40 50 60Data Step

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FWHM Time = 28.2 sFWHM Spatial = 1.53"

Mg II (sub) Mean Velocity ProfileRibbon Characteristics

Conclusions

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• IRIS gives us the most complete view of evaporation/condensation to date

• Evaporation and condensation flows - potentially co-spatial (possible delay)

• Fe XXI line is always completely blue-shifted

• Sources show remarkably similar evolution - flare is a progression of single events

• Condensation time of ~ 60 seconds close to simulation.

• Ribbon size <1.5’’ Excitation time ~ 30 seconds

• Ribbon spatial and temporal scales are essential inputs for modelling (i.e determining the input flux for RADYN)

“The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 606862 (F-CHROMA)”