Particle Acceleration, Flares, and CMEs Hugh S. Hudson SSL, UC Berkeley 13 May 20111

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., T e >>T i and/or v A - >c) 13 May 20112

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 20113

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 20114

5 Trouvelot, 1891 Historical Items First WL flare: 1859 Second: 1891

Three kinds of flares 13 May Stellar (Kowalski et al. 2010) - more later Solar flare (Woods et al. 2004) - First bolometric observations - Understand L X /L tot ~ 0.01 Some planet (HST images) - auroral physics - other planets too

Four environments In a wind: Dungey Magnetar: Duncan In a static structure: Gold-Hoyle With disk: Shu 13 May 20117

8 Impulsive phase and gradual phase of a solar flare Impulsive phase – primary energy release hard X-rays (10s of keV) white light, UV,  waves - 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 (~10 32 X10) Significant role for non-thermal electrons CME acceleration

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 20119

The structure of flare energy 13 May 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 Hudson et al Impulsive-phase contribution to flare TSI (bolometric) energy

How is ground-based observation important in this problem? ROSA * and IBIS on the Dunn Superb image quality with high-resolution spectroscopy 13 May * 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

Results on Low-Lou field 13 May

The essence of the method 13 May 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

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

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

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)

13 May 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

13 May Particle acceleration and radio astronomy: parameter dependences for gyrosynchrotron radiation Stähli et al. 1989

13 May 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

13 May Reznikova et al. observations Model results, 2.46 MeV B required ~ Mm P NT /P gas >> 0.01 Results of analysis

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  -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

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

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