hmi observations of transient phenomena juan carlos martínez oliveros space sciences laboratory, uc...
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HMI OBSERVATIONS OF TRANSIENT PHENOMENAJuan Carlos Martínez Oliveros
Space Sciences Laboratory, UC Berkeley
Charles Lindsey, Hugh Hudson, S. Couvidat, J. Schou, Säm Krucker, P. Scherrer
LoHCo Workshop, Stanford University February 8-9 2011
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Outline
Motivation The 12 June 2010 event Black-light flares Some results The role of GONG
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LoHCo Workshop, Stanford University February 8-9 2011
Motivation
The flare-interior relation was first discovered by Kosovichev and Zharkova (1998).
Sunquakes are the fingerprints of flares in the solar photosphere.
How is this phenomenon produce?
How is it related to the flare energy?
What are the roles of the chromosphere and magnetic field geometry?
Kosovichev and Zharkova, 1998
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LoHCo Workshop, Stanford University February 8-9 2011
Flare Excitation mechanism
Motivation
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LoHCo Workshop, Stanford University February 8-9 2011
Why only a few flares are seismically active?
Till today a couple of tens of sunquakes have been detected.
What make seismically active flares “special”?
Motivation
Is it the flare?Is it the Beam?The excitation mechanism?
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LoHCo Workshop, Stanford University February 8-9 2011
Several mechanisms of seismic waves have proposed:
Chromospheric shocks Photon bombardment (back-
warming) Penetrating particles Magnetic field variations
Motivation
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How to find these sunquakes?1. Looking for waves in the
Doppler data.2. Looking for signatures
associated with the seismicity, namely:
White-light kernels (almost always)
γ-emission (not always this are detected)
Impulsiveness in HXR and microwaves
Motivation
Martínez-Oliveros et al., 2008
Martínez-Oliveros et al.,2007
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LoHCo Workshop, Stanford University February 8-9 2011
The 12 June 2010 event
The flare studied was a GOES M2.0 event in NOAA active region11081, located approximately at N22W45
This was the first γ-ray flare of the new cycle.
It was a highly impulsive event
So, this could be a good candidate.
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LoHCo Workshop, Stanford University February 8-9 2011
Transient Phenomena
A first analysis of SDO/HMI data revealed a decrease of the intensity continuum during the impulsive phase of the flare.
Martínez-Oliveros et al., 2011
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Transient Phenomena
No RHESSI imaging, due to Crab Nebula operations.
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A black light flare?
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A black light flare? II
We now know that the white-light continuum probably is enhanced in all flares, but that for the weaker ones the signal is lost in the glare and fluctuations of the photosphere.
Generally a dimming signature might imply: a) momentary obscuration by overlying material; b) thermal perturbations causing an increased
opacity in the relatively cool chromosphere, hence increased absorption of radiation from the hot underlying photosphere;
c) a non-thermal effect not accessible to standard modeling techniques but with a similar effect (Hénoux et al. 1990).
From Hénoux et al. 1990
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This kind of dimming or dip was reported before for observations of stellar flares (e.g. Cristaldi et al. 1980)
In the Sun is still unclear if this rare phenomenon really occurs.
This should be an achievable task for SDO/HMI.
From Cristaldi et al. 1980
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Transient Phenomena
It was truly a black light flare?
Sadly, the answer is NO.
The HMI Dopplergrams and intensities data consist of a spatial-temporal interpolation, using 12 filtergrams at six different wavelengths and two polarization states, for each observable.
These interpolations, in conjunction with the scanning of the 6173 A Fe I line, were devised to minimize the effects of aliasing (unwanted time-series noise) in p-mode signals.
Because of this, the response of the standard Dopplergrams to a sufficiently rapid white-light flare can be an apparent reduction in intensity preceding the flare, i.e., an apparent “black-light flare” preceding the white-light.
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To avoid the pre-flare artifacts introduced by the negative weighting, NRT data was used.
Martínez-Oliveros et al., 2011
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LoHCo Workshop, Stanford University February 8-9 2011
A transient Blue shift!
The blue shifted transient could signify a photospheric medium moving toward SDO, shifting the absorption line.
Could be also the results of down-flowing heated chromospheric material.
This kind of behavior is atypical.
Hudson (2011) report a red shift using EVE 304Å observations.
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LoHCo Workshop, Stanford University February 8-9 2011
A transient Blue shift!
The blue shifted transient could signify a photospheric medium moving toward SDO, shifting the absorption line.
Could be also the results of down-flowing heated chromospheric material.
This kind of behavior is atypical.
Hudson (2011) report a red shift using EVE 304Å observations.
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LoHCo Workshop, Stanford University February 8-9 2011
A transient Blue shift!
The blue shifted transient could signify a photospheric medium moving toward SDO, shifting the absorption line.
Could be also the results of down-flowing heated chromospheric material.
This kind of behavior is atypical.
Hudson (2011) report a red shift using EVE 304Å observations
Can He II move down rapidly while the photosphere is moving up slowly?
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LoHCo Workshop, Stanford University February 8-9 2011
The role of GONG
Spurious Doppler and intensity signals can be controlled by comparison with GONG observations.
To achieve this cross-calibrations, techniques of cleaning should be applied to GONG data (Lindsey and Donea, 2008).
This techniques must compensate the noise introduced by atmospheric seen.
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LoHCo Workshop, Stanford University February 8-9 2011
The role of GONG
Spurious Doppler and intensity signals can be controlled by comparison with GONG observations.
To achieve this cross-calibration, techniques of cleaning should be applied to GONG data (Lindsey and Donea, 2008).
This technique must compensate the noise introduced by atmospheric seen.