Suprathermal Tails in Coronal Proton Velocity Distributions

Suprathermal Tails in Coronal Proton Velocity Distributions J. L. Kohl, A. Panasyuk, S. Cranmer, S. Fineschi, L. D. Gardner, D.H. Phillips, J. C. Raymond, and M. Uzzo Suprathermal Tails in Coronal Proton Velocity Distributions

Theory of shock acceleration of SEPs M. A. Lee (1983, 2005) developed a theory of coupled turbulent wave excitation and proton acceleration at shocks. Suprathermal Tails in Coronal Proton Velocity Distributions

Theory of shock acceleration of SEPs • In this theory, in order to produce large SEP events, it is necessary for a suprathermal seed particle population to exist after the first encounter of the coronal plasma with a CME shock. The theory requires that .001 to .01 of this proton velocity distribution have an injection speed higher than 2 times the difference between the shock speed and the wave phase speed (~VA in corona). • Alternatively, there could be a pre-existing suprathermal population in the corona that would help to satisfy this requirement. Gopalswamy et al. (2004) found higher SEP intensities when there was a preceding CME within ~24 hours that perhaps left behind suprathermals. Suprathermal Tails in Coronal Proton Velocity Distributions

Theory of shock acceleration of SEPs • The threshold velocity for particle injection is extremely uncertain. There are several lines of evidence that particles of 1000 to 2000 km/s (i.e., 5.2 – 20.7 keV) are preferentially accelerated. From the experimental side, that includes creation of anomalous cosmic rays from pick-up ions. Theories such as the transparency function of Gieseler et al. give similar results. Suprathermal Tails in Coronal Proton Velocity Distributions

Density of Suprathermal Seed Particles Preshock • fi (v): Resonantly scattered Ly constrains the seed particle distribution • fe(v): Thomson-scattered Ly Suprathermal Tails in Coronal Proton Velocity Distributions

kappa needed to provide various population fractions with velocities above the injection velocity • Injection speeds of 940 – 1460 km/s, are 6.1 to 9.7 in units of V1/e • A kappa distribution where .01 - .001 of the population has speeds beyond 6.1 to 9.7 V1/e has a kappa between 4 and 2. • Hence, proton velocity distributions resembling kappa distributions with kappa values in this range and lower are of interest. Suprathermal Tails in Coronal Proton Velocity Distributions

Proton velocity distribution in a diffuse coronal region Kappa = 21.8 ± 7.0 Suprathermal Tails in Coronal Proton Velocity Distributions

Observation of a proton velocity distribution with kappa = 3.5 Kappa = 3.5 ± 0.34 Suprathermal Tails in Coronal Proton Velocity Distributions

20 Jan 2005 Event Suprathermal Tails in Coronal Proton Velocity Distributions

Pseudo-kappa function • Data clearly show asymmetrical wings. • Kappa-function cannot model asymmetrical line profiles. • Idea is to create a function that is close to a kappa-function when the line is symmetrical but allows for a shift of the wings relative to the core. • Some theoreticians use a power-law, so a sum of Gaussian and power-law function seems natural. • For example the plot on the right shows that a kappa-function does not fit the observation. + Suprathermal Tails in Coronal Proton Velocity Distributions

Pseudo-kappa function • We empirically determine the dependency of all parameters (G,A,δ,ρ and σ) of the k- value of approximated function. • The only additional parameter (vs kappa-function) is the Δ – shift which allow us to fit asymmetrical profiles. Suprathermal Tails in Coronal Proton Velocity Distributions

Best fit to data Suprathermal Tails in Coronal Proton Velocity Distributions

Effect of Stray Light Suprathermal Tails in Coronal Proton Velocity Distributions

10 Feb 2006 Suprathermal Tails in Coronal Proton Velocity Distributions

Conclusions • UVCS/SOHO is able to measure proton velocity distributions including departures from Maxwellians. • These observations may lead to testing and refining theories of SEP production. • Work is in progress: line of sight, more observations and archival data analyses to be done. Suprathermal Tails in Coronal Proton Velocity Distributions

Simulation of observation for kappa = 4 • Simulation includes coronal emission assuming kappa = 4, Poisson noise, Binning to UVCS sampling, Random flat field uncertainty, Detector background, Fitting with and without error in instrument profile • Fit with no profile error yields kappa = 3.92 +/- 0.66 • Fit with profile error yields kappa = 3.66 +/- 0.59 Suprathermal Tails in Coronal Proton Velocity Distributions

20 Jan 2005 Event • Kappa is large • 19 Jan 2005, 22:01 + 2:00 Suprathermal Tails in Coronal Proton Velocity Distributions

20 Jan 2005 Event • Kappa = 3.43 ± 1.0 • 19 Jan 2005, 22:01 + 3:30 Suprathermal Tails in Coronal Proton Velocity Distributions

20 Jan 2005 Event 19 Jan 05, 22:01 + 5:30 19 Jan 05, 22:01 + 6:00 Suprathermal Tails in Coronal Proton Velocity Distributions

Interpretation • Phil Isenberg suggested that the non-Maxwellian tails might be associated with heat flux along the magnetic field. • He speculates that the appearance and disappearance of these tails could be due to rotations of the field direction into and out of the line of sight. • He points out that this interpretation probably would not be consistent with a symmetric LOS velocity distribution. Suprathermal Tails in Coronal Proton Velocity Distributions

Interpretation • Next week Gang Li of UC, Riverside will give an SSP seminar describing his recent theoretical finding that a predecessor CME can greatly enhance turbulence upstream of a second shock. This decreases the acceleration time scale at the second shock allowing fast particle acceleration to occur. • To explain the result of Gopalswamy et al., the turbulence would need to be present for several hours after the first shock. • It is not clear if our observations indicate any increase in turbulence following a predecessor shock. Suprathermal Tails in Coronal Proton Velocity Distributions

LASCO C2 image of CME region on 23 & 24 Dec 1996 Suprathermal Tails in Coronal Proton Velocity Distributions

Simulation of observation for kappa = 4 Suprathermal Tails in Coronal Proton Velocity Distributions

UVCS Determinations of Pre-CME Corona • UVCS routinely obtains the densities, temperatures, outflow speeds, ionization states and elemental abundances in the pre-CME corona • Densities obtained by UVCS can be combined with Type II radio burst drift rates to obtain shock speeds • The angle between the shock front and the magnetic field requires the pre-shock field direction, which can be determined from the streamer morphology Suprathermal Tails in Coronal Proton Velocity Distributions

Testing and Guiding Theoretical Models of SEP Acceleration • The measured and derived parameters allow shock acceleration and current sheet models to be tailored to a specific event. • The theoretical models can then predict SEP acceleration, transport and energy spectra for those events. • In situ measurements of SEP energy spectra near the Sun (e.g., by Inner Heliospheric Sentinels) can then be used to test and guide the theoretical models. Suprathermal Tails in Coronal Proton Velocity Distributions

Key Parameters in Theories of SEP Acceleration by shocks • Pre-shock plasma conditions (including the supra-thermal seed particle population) • The shock speed • The compression ratio (which yields the Mach number) • The angle between the magnetic field and the shock motion Suprathermal Tails in Coronal Proton Velocity Distributions

Density of Suprathermal Seed Particles Preshock • fe(v): Thomson-scattered Ly • fi (v): Resonantly scattered Ly constrains the seed particle distribution Suprathermal Tails in Coronal Proton Velocity Distributions

Lin and Forbes Unified Model of a Flare and CME In the Lin and Forbes model, a stressed magnetic arcade begins to rise. A current sheet develops as external pressure forces oppositely directed magnetic field lines to reconnect. The liberated energy heats and drives the CME and drives energetic particles downward producing the flare. Suprathermal Tails in Coronal Proton Velocity Distributions

Suprathermal Tails in Coronal Proton Velocity Distributions