Sheared, Twisted and Tangled: A New View of the Corona from XRT

1
(Sheared,) Twisted and Tangled A New View of the
Corona from XRT

• Leon Golub
• Smithsonian Astrophysical Observatory
• Hinode Science Meeting
• Dublin, 20-24 August, 2007

2
The X-Ray Telescope

• The telescope is a modified Wolter I with a 35 cm
  aperture and a 2.71 m focal length. It has
  on-orbit focus adjustment and provides a flare
  flag to alert the other instruments.
• Properties
• Angular Resolution 1 arcsec pixels
• Encircled Energy 50 within a 1 arcsec diameter
  circle at 0.523 KeV
• Improved temperature sensitivity over the range
  from 130 MK using a back thinned 2048x2048 CCD

Length 3.0 m, Diameter 0.42 m (max), Mass 48.4 kg
XRT Point Spread Function 50 Power Within One
Pixel
3
Comparative Fields of View
EIS can independently offset along the EW axis.
4
XRT Shows Extent of Structure Surrounding ARs
5
A typical corona (QS small AR) requires gt104
dynamic range
Combined 4s 0.5s XRT exposures, Thin Al filter.
6
TRACE and XRT are Complementary
TRACE 173Å 11/13/06
XRT Thin Al 11/13/06
7
XRT Sees Fine Detail in ARsThe High Temperature
Corona is NOT Fuzzy!
1 arcmin
8
B vs. X
MDI Magnetogram
XRT Thin Ti, 1 sec., 11/04/06
9
Detailed views of AR from XRT
Small AR near CMP
Thin Al/Poly 1 sec
10
Temperature Maps
Observations in multiple passbands (focal plane
analysis filters) allow temperature determination
at every pixel in the image. We see finely
resolved highly thermally structured corona in
the AR. 1. Numerous fine, hot threads in AR. 2.
Cooler outer structure of AR 3. Nearby
large-scale loops show high T.. from Reale
etal 2007.
Thermal Map Range is 5.9ltlog Tlt6.6
11
This Talk Case Studies from XRT

• Nonpotential fields around filament (Bobra et
  al.)
• Shear change in flares (Y. Su et al.)
• Sigmoid eruptions (McKenzie et al.)
• Polar jets (Cirtain, Savcheva, et al.)

12
Synoptic Sun-Center Program 5-min cadence, 8-hr
duration
13
Quiet Sun XBP Studies30-sec cadence, 12-hour
duration
14
(Downflows Seen)
Case Study Sheared Fields in X-Flares of
December 2006
Highly sheared inner and unsheared outer loops in
flaring region.
15
Coronal Dynamics in XRT
12/13 22UT to 12/14 10UT at 5-min cadence.
16
Modeling Non-Potential Magnetic Fields In AR
10930 as Observed by Hinode XRT

• M. Bobra, E.E. DeLuca and A. van Ballegoojian
• Smithsonian Astrophysical Observatory
• Cambridge, MA

17
Introduction

• Filaments, or prominences, are thought to be
  embedded in highly sheared and/or twisted
  magnetic structures in the low corona above the
  polarity inversion line (PIL)

PIL
18
Introduction
Active region filaments often have long parallel
strands, suggesting such filaments are embedded
in untwisted (or weakly twisted) field
parallel threads
SVST, 1998/06/21
19
Models of B in/around filaments

• Need to construct 3D models of coronal magnetic
  field based on observations.
• Since corona is a low-ß plasma, the magnetic
  field is close to a non-linear force free field
  (NLFFF).
• Constructing a NLFFF involves inserting a flux
  rope into a potential field and allowing
  relaxation to FF state.
• Then construct a grid of models, varying poloidal
  and toroidal B and compare to observations.

20
Non-Linear Force Free Model (A.A. Van
Ballegooijen, 2003)
2. Construct a potential field vector at every
grid element of 3D computational domain.
1. Read in elements of MDI line-of-sight
magnetogram (2D input).
3. Modify the vectors within a user-defined flux
rope volume based on the location of a filament
observed in a H-a image.
4. Smooth the sharp current sheets at the flux
rope boundary with diffusion and relax into a
non-linear force-free configuration by solving
the ideal MHD induction equation. A solution is
achieved when JxB per pixel is as small as
possible. The theoretical magnetic field
structure is compared to a Hinode XRT image.
21
Data
12 December 2006
Soft X-Ray 161257 UT
Magnetogram 161300 UT
H? 74945 UT
Contour lines of positive (red) and negative
(green) B flux from Kitt Peak SOLIS on an Ha
image of a filament and the path of the flux rope
(blue).
The same B contours overlaid on an XRT image.
An XRT image taken in thin Al-Poly filter.
22
Results B in and Around Filament
12 December 2006
161257 UT
The best fit model has a flux rope with an axial
(toroidal) flux value of 1021 Mx and poloidal
flux value of 1011 Mx/cm and qualitatively
matches the XRT image. In addition, the model
computes the following values Free Energy 7.96
x 1032 Erg Relative Helicity 1.77 x 1043 Mx2
23
Results Current Distribution
A plot of the current distribution at a height of
z 4, which corresponds to the center of the
flux rope. The yellow line represents the x-axis
of the image above, which shows the current
distribution along a cross-section of the flux
rope. White lines represent selected magnetic
field lines from the models result. It is worth
noting that the right-most magnetic field line,
which looks like it is looping over itself, is
actually a sheared line traveling along the axis
of the flux rope.
24
Results Quasi-Separatrix Layers
On the left is a QSL computed from a NLFFF model
of AR 10930 on the right is a QSL computed from
a potential field model of the same active
region. The figure shows the plane z 4 of the
computational volume divided into three areas.
Field lines in the brown and green area intersect
the sides and top of the computational volume.
The QSL calculation was performed only in the
blue area the gradient from dark blue to white
represents weak to strong QSL layers computed
using the method outlined in Démoulin et al.
1996.
25
Magnetic Shear in Two-ribbon Solar Flares

• Yingna Su1,2
• Advisors Leon Golub1, Guangli Huang2
• Collaborators A. A. Van Ballegooijen1, E. E.
  Deluca1,
• J. McCaughey1, K. K. Reeves1, and M. Gros3
• 1. Harvard-Smithsonian Center for Astrophysics,
  USA
• 2. Purple Mountain Observatory, China
• 3. DSM/DAPNIA/Service dAstrophysique, CEA
  Saclay, France
• 2007 SPD dissertation talk, Honolulu, 05/28/2007

26
Outline

• Background (Su et al. 2006, solar physics, 236,
  325)
• Statistical Analysis of Shear Motion
• (Su et al. 2007a, ApJ, 655, 606)
• Conclusions
• Preliminary results from Hinode/XRT
• --Evolution of the sheared magnetic fields in
  AR10930 (Su et al. 2007c, PASJ, submitted)

27
Shear Motion of Footpoints

• EUV brightening pairs used as indicators of
  shear and shear change
• Start close to the magnetic inversion line
  (MIL), but widely separated along the MIL
• (Fig. a, highly sheared)
• End straight across and far from the MIL
• (Fig. f, weakly sheared)

• Strong-to-weak shear motion of the footpoints
• Hard X-ray observations (Yohkoh/HXT) (Masuda,
  Kosugi, and Hudson 2001)
• Ha, EUV, and microwave observations
• (Su et al. 2006 and references therein)

28
Motivation

• Two Questions
• Is the shear motion of the footpoints common?
• Could the change from the impulsive to gradual
  phase be related to the magnetic shear change?
  (Lynch et al. 2004)

29
Distribution of Shear Angles

• Data sample 43 two-ribbon flares
• well observed by TRACE
• Ribbon separation Yes
• Shear motion Yes
• Initial shear angles 50 80
• Final shear angles 15 55
• Change of shear angles 10 60

30
Distribution of TEIP - TCSM

• 15 flares in sample with
• measured shear angle
• corresponding HXR observations
• TEIP - TCSM 0-2 min
• In most events, the cessation of shear change is
  0-2 minutes earlier than the end of the impulsive
  phase.

31
Interpretation
Cartoon of the evolution of the magnetic field in
the standard model of solar flares (from Su et
al. 2006).
This observed shear change can be understood
schematically within the standard model for solar
flares. (e.g., Moore et al. 2001 and references
therein).
32
Results from Pre-XRT Work

• A strong-to-weak shear motion of the footpoints
  is a common feature in two-ribbon flares.
• The cessation of magnetic shear change is 0-2
  minutes earlier than the end of the impulsive
  phase in 10 out of the 15 events, which suggests
  that the change from impulsive phase to gradual
  phase is related to the magnetic shear change.
• The magnetic flux and change of shear angle both
  show strong correlations with the peak flare flux
  and CME speed. A multi-parameter combination
  shows better correlation than individual
  parameter.
• The intensity of solar flare/CME events may
  depend mainly on the released magnetic free
  energy (q12) rather than the total magnetic free
  energy (q1) stored prior to the eruption.

33
Outline

• Background (Su et al. 2006, solar physics, 236,
  325)
• Statistical Analysis of Shear Motion
• (Su et al. 2007a, ApJ, 655, 606)
• Pre-XRT Results
• Preliminary results from Hinode/XRT
• --Evolution of the sheared magnetic fields in
  AR10930 (Su et al. 2007c, PASJ, submitted)

34
Observational Data

• Target
• NOAA AR 10930 where two X-class flares occurred
• X3.4 flare on 2006/Dec/13
• X1.5 flare on 2006/Dec/14
• Data from
• Hinode/XRT
• Hinode/SOT
• TRACE
• SOHO/MDI
• Topic
• Evolution of the sheared core field prior to,
  during, and after the flares.

35
Formation of the sheared core field
XRT observations of sheared field formation From
0019 UT on Dec 10 To 1243 UT on Dec 12

• SOT observations of
• Emerging flux
• West-to-east Motion
• CCW Rotation
• in the Lower sunspot

36
Part of the sheared core field erupted, while
part stayed behind.
X1.5 flare on 2006/12/14
X3.4 flare on 2006/12/13
37
Pre-flare vs. post-flare sheared core field (Dec
13 flare)

• Post-flare core field is less sheared than the
  pre-flare core field
• Re-formation or only partial eruption of the
  filament

38
Pre-flare vs. post-flare sheared core field (Dec
14 flare)

• Post-flare core field is less sheared than the
  pre-flare core field
• Re-formation or partial eruption of the filament

39
Shear-Change Summary

• The formation of the sheared core field is caused
  by the CCW rotation and west-to-east motion of an
  emerging sunspot.
• XRT observations of incomplete (partial)
  eruption of the sheared core field may explain
  the continued presence of the filament after the
  flare.
• Post-flare core field is much less sheared than
  the pre-flare field, consistent with scenario
  that the energy released in the flare is stored
  in the highly sheared core field.
• Next step compare pre- and post-flare NPFF
  fields.

40

• Part of the sheared core field erupted, part
  stayed behind.

41
Growth of Postflare Cusp
Note downward-moving cooling fronts.
42
XRT Observations of a Coronal Sigmoid

• David E. McKenzie
• Richard C. Canfield
• Montana State University

43
Outline

• Background (reminder of sigmoids)
• Models of sigmoid formation
• The XRT data
• Model predictions
• Sigmoid shape
• Why some loops are hot bright
• When some loops are hot bright
• Sigmoid evolution
• Sigmoid eruption
• Summary of key results

44
Background
Sigmoid coronal active region with S or
reverse-S shape.

• Rust Kumar (1996)
• Sterling Hudson (1997)

XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
45
Background
XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
46
Background
Doesnt erupt
Erupts
Canfield, Hudson, McKenzie (1999) GRL, 26, 627.
XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
47
Models of Sigmoid Formation

• Rust Kumar Pevtsov Canfield
• Twisted flux rope
• Titov Demoulin
• Twisted flux rope embedded in ambient field
• Bald patch separatrix surface
• Fan Gibson
• Twisted flux rope embedded in ambient field
• Current sheet created during kink instability

48
Models of Sigmoid Formation

• Rust Kumar Pevtsov Canfield
• Twisted flux rope

• Provides no useful description of heating
  mechanism, so not considered further.

49
Models of Sigmoid Formation

• Titov Demoulin
• Bald Patch When a flux rope emerges, there are
  places where the magnetic field is tangential to
  the photosphere and concave upward.

Initial bald patch
Bifurcated bald patch
XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
50
Models of Sigmoid Formation

• Titov Demoulin
• Bald patch separatrix surface

51
Models of Sigmoid Formation

• Titov Demoulin
• Bald patch separatrix surface

BP


52
Models of Sigmoid Formation

• Fan Gibson
• Current sheet created during kink instability

53
Models of Sigmoid Formation

• Fan Gibson
• Current sheet created during kink instability
• At leading edge of kinking flux rope

54
The XRT Data
Hinode/XRT, 1 arcsec/pixel, cadence of one image
per 10-30 seconds
55
Model Predictions Shape
XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
56
Model Predictions Shape

• The XRT data suggest two J-shapes terminating in
  bald patches near polarity inversion line,
  consistent with BPSS model of Titov Demoulin.

XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
57
Model Predictions When loops are hot/bright

• Fan Gibson
• Only when kinking
• Requires motion
• Time scale of 10-40 Alfvén crossing times (i.e.,
  20-60 minutes)
• Titov Demoulin
• Any time after formation of bald patches
• Does not require motion

XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
58
Model Predictions When loops are hot/bright

• This structure held its sigmoid shape for two
  full days before erupting.
• Discernable as 2-J sigmoid from at least
  10-Feb, 1107UT (maybe as early as 09-Feb,
  1122UT).
• Erupted 12-Feb, 0700UT.
• 2 days gtgt 20-60 minutes

XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
59
Model Prediction Evolution

• Where does the flux rope come from?
• Either it emerges, already formed, from beneath
  the surface, or
• Forms in the corona by multiple successive
  reconnections.
• In the Titov Demoulin picture, as the flux rope
  emerges, the bald patch bifurcates and spreads
  apart.
• The straight part of the j should lengthen and
  overlap more.
• The elbows of the sigmoid should expand also,
  as the separatrix surface expands to enclose the
  emerged flux rope.

60
Model Prediction Evolution
61
Model Prediction Evolution

• Tracking best-guess location of BPs, separation
  increase of 26 Mm in 40 hours
• Tracking greatest extent of sigmoid elbows,
  overall length increase of 64 Mm in 40 hours

Preliminary!
62
Eruption

• The sigmoid erupted at 0700 UT on 12-Feb.
• A bright bar-shaped feature is observed rising
  from the central part of the sigmoid.
• Possibly the flux rope?
• Also in December flares
• This eruption has features consistent with kink
  instability, and BPSS.

XRT Sigmoid Kosugi Memorial Workshop, NAOJ,
April 2007
63
Eruption

• The bar-shaped flux rope rotates CW as it lifts
  off.
• Direction of rotation is consistent with expected
  rotation from kink instability
• To conserve magnetic helicity, writhing of flux
  tube keeps same sense as twist in field lines.
• Right-handed (left-handed) flux rope, when
  kinking, should rotate CW (CCW)

64
Eruption

• The flare arcade is just as predicted by BPSS
  model.
• Small cusped arcade along the PIL, beneath the
  flux rope.
• The separator of BPSS corresponds to the X-line
  of CSHKP model.

65
Key Results

• Sigmoid shape
• The data match the prediction of Bald Patch
  Separatrix Surface model (specifically, the 2-j
  shape).
• When are the loops hot bright
• Duration of sigmoid is more consistent with BPSS
  model (2 days 20-60 minutes).
• Sigmoid evolution
• Observed growth of sigmoid is consistent with
  emergence of twisted flux rope from beneath the
  photosphere (born, not made).
• Sigmoid eruption
• Rotation of bar-shaped ejected feature is
  consistent with prediction of kinking flux rope.
• Location of arcade matches prediction of BPSS
  model.

66
Does XRT See Slip-Running Reconnection?
XRT Observation
Theoretical Model
67
Polar JetsNumerous Jet-like Events Observed
Image Cadence 30 sec.
68
Coronal Dynamics in XRT North Polar XBP and Jets
11/23/06 Thin Al/Poly 4s. exp. 30-sec cadence,
7-hour duration
Mass loss estimate Np1037 per event Event
frequency 10/hr Net flux gt1012 p/cm2/s Avg.
solar wind flux 1013 p/cm2/s
69
LEFT XRT Polar Jet movie RIGHT Shimojo,
M., and Shibata, K., ApJ 542, 1100 (2000). From
the Hudson Solar Cartoon Archive
(http//solarmuri.ssl.berkeley.edu/hhudson/cartoo
ns/overview.html)
70
A typical coronal jet seen with XRT
Jet seen in Al_poly filter on 01/17/07 1311
UT. The jet has reached its maximum length.
..\..\..\..\Application Data\SSH\temp\jetraw.eps
71
Determination of jet velocity
One of four methods developed to determine
velocities Central vertical rectangle of image
is summed across rows to yield a single
column. Images are then placed sequentially
side-by-side to produce a time-ordered
image. Slope of near-vertical feature gives
velocity of outward-moving front.
72
Summary of velocity results for sample of 101 jets
73
Plot of jet locations
Jets are preferentially seen in coronal holes.
Is this real or a visibility effect? Under
investigation.