Multi-Height Full Stokes Polarimetry of a B-Class Flare Tom Schad – in collaboration with – Ali Tritschler & Matt Penn CANFIELD-FEST Aug 8 – 11, 2010

Image courtesy A.O. Benz, “Flare Observations” Living Rev. Solar Phys. 5 Introduction 9 August 20102Tom Schad - Canfield-Fest  How do flares acquire and release free magnetic energy into thermal and nonthermal energy? The Problem: Constraining the Problem:  Quantifying the transfer of energy…usual methods:  multi-spectral diagnostics  energetic particle spectrum measurement 1 AU)  Evaluating magnetic field topology from photospheric field. This talk  A not-as-usual method  chromospheric polarimetry of flaring regions

A few previous studies…  Hénoux & Semel, 1981  Penn & Kuhn 1995  Metcalf, Leka, & Mickey 2005  Xu et al. 2006, 2007  Sasso et al  Firstova et al August 2010Tom Schad - Canfield-Fest3 Achieving polarimetric signals from the chromosphere is observationally and as well as theoretically challenging.

Why Multi-Height Flare Polarimetry? 9 August 20104Tom Schad - Canfield-Fest Assumed Non-Linear Force-Free Photospheric Field Extrapolation ‘Actual?’ force free boundary for extrapolation Field Reconstruction Field Topology Advantage Chromospheric Zeeman Polarimetry More accurate topology for examining of flaring region skeleton Direct measure of total field energy Probe of not-well classified horizontal fine structure in chromosphere..perhaps flaring role Accelerated Particle Dist. Measure Measuring spectra of accelerated particles (1 AU) Impact Linear Polarization Measure of accelerated particle anisotropy in solar atmosphere.

9 August 20105Tom Schad - Canfield-Fest Line Formation Complex NLTE formation Weak polarization Large range of contribution heights -Photospheric contamination Necessary Observations Interesting fields largely horizontal Fine scale structure Large scale features [+large Grad(V LOS )] Short scale dynamics Technical Needs Multi-wavelength spectropolarimetry, large field of view, high cadence, diffraction- limited, high spectral resolution, high polarization accuracy, CHALLENGES

9 August 20106Tom Schad - Canfield-Fest He I - promising diagnostic of vector magnetic fields in upper chromosphere Solanki et al., 2003, 2004 Observational Magnetic Field Reconstructions NLFF Extrapolation Coupled Zeeman, Hanle, Atomic Polarization, PB effect inversions possible HELIX+ and HAZEL codes available

the Dunn Solar Telescope, May 2010 FIRS  Fe I 6302, Si 10827, He I – Full Stokes Polarimetry IBIS  Ca II 8542 – Full Stokes  Whitelight Imaging + G-Band Imaging + DST High Order Adaptive Optics + Supporting SOLIS (10830 spectroheliograms & 8542 L)and McMath/Pierce (10830 – Full Stokes) 9 August 20107Tom Schad - Canfield-Fest

FIRS The Facility Infrared Spectropolarimeter at the Dunn Solar Telescope  Multi-Spectral Diff.Limited Slit-Spectropolarimeter  Simultaneous IR & Vis Full Stokes Polarimetry  Multi-Slit (Fast scanning of solar image across slit unit)  Large Field of View (up to ~ 170” x 70”)  Currently operates in 630, 1565, and 1083 nm spectral windows 8 Raw VIS Frame – 630 nm Raw IR Frame – 1083 nm Two Beams Slit 1 Slit 2 Slit 3Slit 4 Sunspot in Slit 2 Fe I nm Fe I nm Si I nm He I 1083 nm Triplet Telluric Two Beams Jaeggli et al. (2008)

IBIS The Interferometric Bidimensional Spectro(polari)meter Raw IBIS Frame with Dual-Beam Polarimetry FOV ~ 40” X 80”  Builds 3(or 4) dim data cubes [X, Y, LAMBDA, (STOKES STATE)] using tunable scanning of a given spectral window or combinations of spectral windows  Usable Range: 5800 Å Å  High Spectral ( R≥ ), spatial ( ≃ 0.2″), and temporal resolution (several frames per second) 9 August Tom Schad - Canfield-Fest Cavallini (2006); Reardon & Cavallini (2008)

May 25, 2010 Operations  Ca II λ8542 Å  Full Stokes Dual-Beam Polarimetry  20 spectral points (Stokes definition modulation sequence at each wavelength + simultaneous whitelight continuum frames)  36 second period for all 120 [i.e. 20-λ x 6-states] measurements  Near continuous scanning between 13:00 and 18:00 UT  Unbinned Polarimetry RMS noise ~ 1x10 -2 I C 9 August Tom Schad - Canfield-Fest FIRS IBIS  Visible Arm: Fe λ 6301 Å and λ 6302 Å (1 pm spectral disp)  Infrared Arm: Si λ Å and He I λ Å (3.8 pm spectral disp)  Full Stokes Dual-Beam Polarimetry  4-slit unit used  FOV ~168” x 70”  Deeper integration scan (1 hour for full FOV scan…FOV can be scan ~ 20 min)  Angular resolution: 0.29”  RMS 029” res ~ 2x10 -3 I C

NOAA AR May 25, 2010 μ ≈ 0.6 S15 °, W35° FIRS slit aligned perpendicular to Earth’s Horizon (reason for FOV rotation between scans) IBIS FOV FIRS FOV 9 August Tom Schad - Canfield-Fest OBSERVING TARGET

A B6.5 Flare on May 25, August Tom Schad - Canfield-Fest H-alpha movie From BBSO Full Disk Images

The Observed Flare - Context Put in continuum int map, hewid equivalent width map, IBIS frame (c.int + lcen), & BBSO flare map 9 August Tom Schad - Canfield-Fest

First, a photometric/spectroscopic look: 9 August 2010Tom Schad - Canfield-Fest14 GOES X-ray Flux IBIS 8542 Line Center Intensity Movie H alpha and Ca II 8542 intensity follows closely the X-ray flare flux.

He I Flare Response 9 August Tom Schad - Canfield-Fest Photoionization-Recombination (PRM) – due to coronal EUV Collisional excitation Collision ionization (CM)  In large flares, emission common.  Emission seen in small flares, but spatial extent is often limited.  Formation of flare emission not well known [You et al. 2001]  Most likely enhanced coronal EUV deepens some spectra during event. 13:05:39 UT 14:15:24 UT 15:20:29 UT 16:25:59 UT Primary formation processes [Avrett et al. 1994; Ding et al. 2005]:  Hard to distinguish. FIRS Observations

He I – Red Line Intensity He I – Blue Line Intensity Continuum Intensity Near Si I August Tom Schad - Canfield-Fest

9 August Tom Schad - Canfield-Fest A Possible Nonthermal Effect to He I Line Formation Ding et al. (2005) suggest a nonthermal electron beam may deepen absorption prior to flare heating excited emission Slit #3 Flare Light Curve

Quick note on velocity diagnostics 9 August Tom Schad - Canfield-Fest Deepened absoption in contrast to 8542, 6563, etc., allows for better velocity determination.

9 August Tom Schad - Canfield-Fest Magnetic Energy Injection at Flare Location Hagyard et al  Flare location association with large magnetic shear along neutral line [Hagyard et al. 1990]  Injection of energy into corona derived from displacement of magnetic features (emergence/cancellation, MMFs, sunspot rotation [Regnier & Canfield 2006])  Injected energy can be estimated from transverse field motions [Kusano et al. 2002]: Flare Polarization Observations….

13:05:39 UT 14:15:24 UT 15:20:29 UT 16:25:59 UT FIRS Scan Start Times 9 August Tom Schad - Canfield-Fest TEMPORAL EVOLUTION OF PHOTOSPHERIC FIELD VECTOR Significant Transverse Field Horizontal Motion of Magnetic Field FLARE START: 15:46 UT

Photosphere/Chromosphere Field Comparison 9 August Tom Schad - Canfield-Fest 13:05:39 UT 14:15:24 UT 15:20:29 UT 16:25:59 UT Chromospheric Vertical Field More Diffuse Field more ‘pinched’ in chromosphere?

Chromospheric Magnetic and Velocity Structure 9 August Tom Schad - Canfield-Fest 13:05:39 UT 14:15:24 UT 15:20:29 UT 16:25:59 UT

9 August Tom Schad - Canfield-Fest Chromospheric Magnetic and Velocity Structure 9 August Tom Schad - Canfield-Fest 13:05:39 UT 14:15:24 UT 15:20:29 UT 16:25:59 UT BSE?

Finally, a look at the full Stokes Spectra… Flare Emission Stokes Spectra 9 August Tom Schad - Canfield-Fest  Only a preliminary look, as reduction needs work. Flare in emission As seen in Stokes V map, flare location near polarity reversal Hint of Stokes U structure Curious Stokes V signal in flare.  Red component < noise  Blue comp. shows Zeeman profile. Perhaps optical thickness difference?

IBIS 8542 Stokes Vector Movies 9 August Tom Schad - Canfield-Fest Complete polarization calibration (unfortunately poor MPEG quality)

8542 PreFlare vs. Flare Emission Stokes Spectra 9 August Tom Schad - Canfield-Fest  Flare fibrils show distinct 8542 emission  Stokes I  U crosstalk, but clear but complext changes in Q, U

8542 Stokes Vector Time Series Flare Start 15:46 Flare Peak 15:51 Flare End 15:55 9 August Tom Schad - Canfield-Fest Anti-symmetric Stokes V profile turned anomalous by flare? Stokes U amplitude seems to increase during flare? What could explain it?

9 August 2010Tom Schad - Canfield-Fest28 A few possible causes…. [Firstova et al. 2008]  Impact Polarization  Formation Height Change?  Field Topology Shift?  Not real? Instrumental, seeing cross-talk? Effect of limited spectral resolution? Temporal effect?

Concluding Remarks  FIRS and IBIS join observations offer beneficial new diagnostics and instrumental opportunities for flare studies.  He I triplet could be an important tool for field topology and evolution assessment.  Polarization signatures within flare for and 8542 shows interesting complex behavior.  Stay tuned… 9 August Tom Schad - Canfield-Fest Thank You