Presentation on theme: "Investigating the Origin of the Long-Duration High- Energy Gamma-Ray Flares Gerry Share, Jim Ryan and Ron Murphy (in absentia) Steering Committee Overseer."— Presentation transcript:
Investigating the Origin of the Long-Duration High- Energy Gamma-Ray Flares Gerry Share, Jim Ryan and Ron Murphy (in absentia) Steering Committee Overseer G. de Nolfo
One of the first observations and measurements of a Long Duration Gamma Ray Flare. CGRO/EGRET observation of the 1991 June 11 X12 solar flare with emission observed for at least 8 hours. Note all the flares were intense with strong impulsive phases. The much improved sensitivity of Fermi has yielded many more such events reviving the discussion.
Most intense and longest duration LDGRF. Proton spectrum >300 MeV softens over time. Proton spectrum below 300 MeV is harder 2012 March 7
Emphasize 2011/12 March 7 flares How can we explain LDGRFs (protons >300 MeV) that last from tens of minutes to up to 20 hours? Is this a single process or possibly two that we are observing (e.g. acceleration of trapped population and CME/shock origin)? What theories can to apply to this problem? Direct LAT observations and lack of over-the-limb >100 MeV events suggest interactions near the AR. Is this explainable for long time intervals? Typical delays between impulsive peak and rise of sustained emission-- 1 to a few tens minutes. How do these compare with SEP release times for the same events? The numbers of protons at the Sun during the flares appear to be smaller (10-20%) than those in the time-extended phase.
How do we explain the striking association with fast/broad CMEs and flares with >100 keV emission? Sub-MeV ion seed population?Very preliminary evidence that numbers of protons >200 MeV in space and at the Sun are comparable (2012 May 17 GLE exception?) What about spectral and duration comparisons? PAMELA?Are there other solar/heliospheric characteristics associated with events?
No LAT >100 MeV events observed when the Active Region behind the Sun ☛ high-energy protons interact close to AR. Seems to be contrary to the disparate locales of the 2012 March 7 event.Slowest CME associated with a LAT event 605 km/s (but event may only have lasted 10’s min) ☛ Broad/fast CMEs critical role in release of high-energy protons at Sun. But, is this the Big Flare Syndrome?All LAT events are accompanied by >100 keV HXRs ☛ Can take the 100 keV emission as a surrogate for multi-MeV ions, implying flare activity is required.18 of the 21 LAT events to date have clear association with SEPs ☛ Processes producing LAT events and SEPs related in some events. But, is this the Big Flare Syndrome?
02-08 UT08-11 UT
The Model 1.Impulsive phase Ions injected into large (length L ) magnetic structure MHD turbulent plasma contains particles (λ ≪ L) Particle diffuse to ends of loop and precipitate onto dense atmosphere Ions are accelerated by Fermi process attaining high energies ☛ Delayed and prolonged high energy emission 9
10 Spatial diffusion time: 32 hInjection occurs 12% from loop endStochastic acceleration time: 6.4 hLoop length: 3.5 R ☉ Injection energy 20 MeVPrecipitation energy 300 MeVMean free path 260 km X1 flare X5 flare Spatial diffusion time: 4.4 hInjection occurs 15% from loop endStochastic acceleration time: 0.88 hLoop length: 1.2 R ☉ Injection energy 20 MeVPrecipitation energy 300 MeVMean free path 70 km
11 Other modeling ideas CMEs: How would one get the get the particles back from the shock to the low corona? Time scale, efficiency, energy? Raymond: Large scale current sheets can be present for long times. Do they carry enough electric field coherently? Do CMEs improve or hinder the coronal trap concept, by either disrupting the trap or creating one.
Pre-Existing L-S Structures X1 flare CME After Flare Extended region of opening field lines & possible large-scale connecting loop(s) Dave Webb
DateLocationClass CME Speed Pamela > 200 MeV Pamela > 500 MeV Fermi/LA T >200 MeV Fermi/LA T >500 MeV Ratio Np(Sun)/ Np(SEP) T00:02 N17E27X x x x x T01:25 N05W77M x x x x T03:38 N33W21M × × x x T17:37 N33W85X × × x x T06:16 S21W54M x x x x Looking for correlation between IP and flare ions Using PAMELA data >500 MeV, de Nolfo concludes no obvious correlation present, but differs from Share et al.
AMS—Alpha Magnetic Spectrometer on Space Station and operating
Speaking of turbulence Bill Matthaeus Developing 3-d turbulence model. Reveals heretofore unappreciated processes that provide enhanced or additional energization of particles.
Two stage acceleration by interaction of turbulence & reconnectionStage 0: intermittent cascade produces hierarchy of coherent current structures Stage I: particle with smaller gyroradii (electrons/subAlfvénic protons) parallel accelerate INSIDE current sheets/reconnection regions Escape: finite size, pitch angle scattering, FLRW Stage II: particles now OUTSIDE current structure (in 2D, between X-point & O-point) can be trapped in some islands/flux tubes; now can experience: – 2nd order acc. due to Alfvénic island oscillations (2D or 3D) – 1st order betatron spin-up due to in-plane Electric field gradients (3D!)