Rapid Changes in the Longitudinal Magnetic Field Associated with the July 23 2002 gamma-ray Flare

1
Rapid Changes in the Longitudinal Magnetic Field
Associated with the July 23 2002 gamma-ray Flare

• Vasyl Yurchyshyn, Haimin Wang, Valentyna
  Abramenko,
• Thomas J. Spirock and Säm Krucker
• Big Bear Solar Observatory, Big Bear City, CA
  92314
• Space Sciences Lab, University of California,
  Berkeley, CA 94720

2
Introduction

• Earlier studies report on flare related
  variations in the magnetic field
• local changes associated with the major polarity
  inversion line (Severny 1964 ZverevaSeverny
  1970 Moore et al. 1984 WangTang 1993 Wang et
  al. 1994 KosovichevZharkova 1999, 2001 Spirock
  et al. 2002 Wang et al. 2002)
• changes of magnetic shear (Chen et al. 1994, Wang
  et al. 1994, Hagyard et al. 1999)
• global changes, when both the photospheric and
  the coronal field of an active region are
  involved in a flare (van Driel-Gesztelyi et al.
  1997, Aschwanden et al. 1999 Abramenko et al.
  2003).
• Wang et al. (2002) studied six X-class flares and
  found impulsive and permanent changes in the
  magnetic flux during the flares, which were not
  balanced
• the leading flux always increased while the
  following tended to decrease.
• Spirock, Yurchyshyn and Wang (2002) and Wang et
  al. (2002) explained the unbalanced flux increase
  by several possible mechanisms
• i) emergence of a very inclined flux tube,
• ii) change of the orientation of the magnetic
  field and
• iii) expansion of the preceding sunspot as a
  result of the relaxation of the magnetic field
  after a flare.

3
Goal of the Study

• In the present paper we will show that the first
  two mechanisms (new flux
• emergence and the orientation and/or
  inclination) may indeed be
• responsible for the observed changes.
• We will analyze Halpha, magnetograph and X-ray
  data for the 2002 July 23 gamma-ray flare, which
  occurred in Active Region NOAA 0039. It was a
  long duration event that peaked around 0028UT. We
  will focus here on the evolution of the magnetic
  field associated with the flare.
• To understand the changes that the magnetic field
  underwent during the early phase of the flare, we
  reconstruct basic signatures of a 3D coronal
  magnetic field by using a linear force-free field
  extrapolation model.

4
The 2002 July 23 Gamma-ray Flare
BBSO H? at 0027 UT
BBSO DMG at 0037 UT
Contours are RHESSI 12-20 keV (red) and 100-150
keV (blue)
HXR emission, which dominated above 30 keV, was
related to the photospheric foot points, while at
lower energy range a gradual coronal HXR source
had been found (Krucker, Hurford and Lin 2003).
BBSO H? at 0027 UT
5
Magnetic Flux From SOHO/MDI

• The flux time profiles are plotted for
• the following (positive) and the leading
• (negative) polarity by the thin solid
• lines.
• Immediately after the flare (at 0047UT,
• the right vertical dashed line) the total
• following (positive) flux decreased by
• about 14, while the total leading flux
• increased by approximately 6.
• These changes were permanent and
• the flux did not return back to the pre-
• flare level after the flare ended.

Bold lines are RHESSI flux in the 100 to 150 keV
energy range
6
Magnetograms From BBSO/DMG

• BBSO the leading (S) flux up by about 5, while
  the following (N) flux down by about 13 (The
  corresponding MDI flux changes are 6 and 14).
• Circled area the northern HXR source at the
  flare onset the peak intensity increased from
  800Gs to -1100Gs S flux up by 30 the penumbral
  bridge became wider (compared the red contours)
  the transverse field has changed orientation. New
  flux emergence?
• Boxed area the northern HXR source and the foot
  points of the PFL system in the late phase of the
  flare S flux up threefold the transverse field
  has changed orientation . Change in the
  inclination?

7
Magnetic Flux Changes From Simulated Data
The simulated magnetogram contains an S-shaped
NL and, projected on the east limb, it resembles
the observed magnetogram. A pre- (a-0.025
arcsec-1) and a post-flare (a-0.001 arcsec-1)
magnetic field was simulated by matching general
curvature of the calculated field lines to the
observed Ha fibrils and post-flare loops.
The magnetograms were projected at the east solar
limb (l-65) and the line-of-sight components
were determined. The leading (S) flux increased
by 24, while the following (N) flux decreased by
about 59. Note, that the observed data gives 6
and 14, respectively.
The flux variations in the simulated
line-of-sight magnetograms are due to changes in
the inclination and/or orientation of the
magnetic field.
8
What Can We Learn From the Fact That

• i) the magnetic flux
• and
• ii) the inclination of the magnetic field
• change rapidly during a major flare?

9
Magnetic Flux Changes and Flare Models
flux rope models eruption of a pre-existing (in
equilibrium) flux rope and a gradual ( 1-2
hours) reconnection process
erupted flux rope
reconnection
reconnection models rapid formation of an
unstable flux rope by reconnection between
sheared arcades
erupted flux rope
sheared arcades
reconnection
Figures courtesy of Amari et al. 2003, ApJ, 585,
1073
10
Summary

• We presented study on rapid changes in the
  magnetic field associated with the July 23, 2002
  gamma-ray flare.
• MDI and BBSO data showed that immediately after
  the flare the leading polarity of the magnetic
  field had increased by 2x1020 Mx (6), while the
  following polarity decreased by 1x1020 Mx (20).
  The observed changes were permanent and seem not
  to be caused by variations in the profile of the
  spectral lines that were used to measure magnetic
  fields.
• We distinguish two separate locations, which show
  the most dramatic changes in the magnetic field.
• a location, which was most probably associated
  with new flux emergence and it showed an increase
  in the magnetic field and a new penumbral area
• a location, which coincided with foot points of a
  growing post-flare loop system and it showed a
  shift of the neutral line in longitudinal
  magnetograms.
• Linear force-free field simulations showed that
  the re-orientation of the magnetic field was
  capable of producing the observed changes in the
  total magnetic flux.