1

Particle Acceleration, Flares, and CMEs

Hugh S. HudsonSSL, UC Berkeley

13 May 2011

2

Particle acceleration

• Flare energy appears largely in ~20 keV electrons• Comparable energy may also appear in ~20 MeV ions• A CME shock may convert 10% of the total flare

energy into “solar cosmic rays”• Therefore, “heating” in a flare may be

catastrophically non-thermal (e.g., Te>>Ti and/or vA->c)

13 May 2011

3

Implications

• To understand flare energy transformation, we need the diagnostic capability to follow the intrinsically nonthermal evolution of the plasma

• Ground-based observations provide the best resolution and breadth, and are essential to progress – optical spectroscopy, radio magnetography, microwave particle diagnostics

13 May 2011

4

History of flare research

• The photosphere (Carrington 1859; ?)• The chromosphere (Hale, Svestka, Zirin)• The corona (Wild, Friedman, Peterson)• The lower atmosphere (current hot topic)

- note that “sunquakes” actually link the corona back into solar interior structure

13 May 2011

513 May 2011Trouvelot, 1891

Historical ItemsFirst WL flare: 1859

Second: 1891

6

Three kinds of flares

13 May 2011

Stellar (Kowalski et al. 2010) - more later

Solar flare (Woods et al. 2004) - First bolometric observations - Understand LX/Ltot ~ 0.01

Some planet (HST images) - auroral physics - other planets too

7

Four environments

In a wind: Dungey

Magnetar: Duncan

In a static structure: Gold-Hoyle

With disk: Shu13 May 2011

813 May 2011

Impulsive phase and gradual phase of a solar flare

Impulsive phase – primary energy release• hard X-rays (10s of keV)• white light, UV, mwaves - broad spectrum • duration < few minutes• intermittent and bursty time profile, 100ms• energy deposition in the chromosphere

Gradual phase - response to input• thermal emission (kT ~0.1-1 keV)• rise time ~ minutes• coronal reservoir filling up

Impulsive phase: • Large fraction of total flare energy released (~1032 ergs @ X10)• Significant role for non-thermal electrons• CME acceleration

9

Why is a flare interesting?

• It “pings” the star, as a test pulse, with rich diagnostic potential

• Its mechanisms embrace an amazing breadth of radiative and mechanical phenomena

• The core problem – how energy is stored and released – is not solved yet

13 May 2011

10

The structure of flare energy

13 May 2011

• Continuum emission (WL/UV) from the chromosphere in a 32 arc s domain• From other data, we understand that this is the main flare luminosity• It is very intense, and mostly unresolved in space and time

Woods et al. 2004

Hudson et al. 2006

• Impulsive-phase contribution to flare TSI (bolometric) energy

11

How is ground-based observation important in this problem?

• ROSA* and IBIS on the Dunn• Superb image quality with high-resolution spectroscopy

13 May 2011*Remarkable white-light feature in a C2.2 flare; Jess et al 2008

The coronal magnetic field in the core of an active region

• Studies of coronal energy storage by two young researchers, Malanushenko and Sun (SDO conference)

• Such knowledge is fundamental to the central flare problem• We are not quite there yet, either theoretically or

observationally

Anna Malanushenko’s new method

14

Results on Low-Lou field

13 May 2011

15

The essence of the method

13 May 2011

• This is not a boundary-value problem• Knowledge of the field geometry within the volume to be represented is assimilated into the model• Knowledge can come from high-resolution coronal imaging, or magnetography• Knowledge could also come from the very precise gyroresonance condition

Lee et al. 1998

Xudong Sun’s Movie

• Xudong is a student of Todd Hoeksema, and the methods are those of Wiegelmann• Movie shows horizontal current density along line• The flare appears to correspond to a collapse of the coronal current system

Sun’s Results

18

How is ground-based observation important in this problem?

• The estimates of free energy from vector magnetograms seem to have two problems- A step-wise change has not been demonstrated reliably, as in Sudol & Harvey (2005) for the LOS field- The estimated energies are systematically too small

• The vector observations have several problems, including insufficient resolution and cadence

• More qualitative methods (H. Wang and BBSO) strongly suggest that flare-related field changes involve an implosion

13 May 2011

19

How is ground-based observation important in this problem?

• Spectroscopy leads to physical understanding • Ideally, imaging spectroscopy (each pixel at high resolution) is

needed (microwave…, optical)

13 May 2011

Kowalski et al (2010):Stellar flare on dMe star YZ CMi with ARC 3.5m at APO. Black is flare, purple is quiet star, red is fit with 10K blackbody + Balmer continuum model.

Neidig et al (1983): solar flares (NSO/USG)

Donati-Falchi et al (1985): Solar flare (NSO/USG)

2113 May 2011

Q: The white-light flare continuum, even though it contains a large fraction of the flare energy, remains mysterious – how does the magnetic field of the low corona collapse to create a “small temporary A0 star in an M (or G) star atmosphere?”

A: Via particle acceleration

2213 May 2011

Particle acceleration and radio astronomy: parameter dependences for gyrosynchrotron radiation

Stähli et al. 1989

2313 May 2011

Tracing the accelerated particles

• Unusual solar flare of 24 August 2002• Nobeyama 17 and 34 GHz observations at 10” resolution• Monte Carlo simulations of dynamics and estimation of physical parameters

Reznikova et al. 2008

2413 May 2011

• Reznikova et al. observations • Model results, 2.46 MeV• B required ~200 G @ 40 Mm• PNT/Pgas >> 0.01

Results of analysis

25

How is ground-based observation important in this problem?

• Non-thermal energy release dominates flare development and is probably the key to CME initiation as well

• Access to high-energy particles traditionally involves X-ray and g-ray observations (e.g., RHESSI) from space

• Radio techniques also give us access to the key signatures of accelerated particles at high resolution, excellent sampling, and spectroscopic detail

13 May 2011

26

What about CMEs?

• Fast CMEs are closely associated with flare development and particle acceleration (e.g. Temmer et al., 2010)

• The energy needed to open the field must come from the lower atmosphere

• “Stealth” CMEs (e.g. Robbrecht et al. 2009) may be a different matter

13 May 2011

27

Conclusions

• CMEs, flares, and particle acceleration involve difficult microphysics that is best accessible at high resolution and with spectroscopy

• The chromosphere (or lower solar atmosphere in general) is the place to look for this physics

• There are many opportunities for ground-based observations that can address some of these problems

13 May 2011