Observation of impulsive Solar Flares with the Fermi

Observation of impulsive Solar Flares with the Fermi Large Area Telescope ! Nicola. Omodei@stanford. edu Fermi LAT and GBM Collaborations

Gamma-ray emission from the Sun • The sun is a steady, faint source of gamma-rays (produced by the interactions of CR with the solar atmosphere and with the solar radiation field); • High-energy emission (up to Ge. V) has been observed in solar flares: • In the past decades, only two long-lived (hours long) gamma-ray emissions were observed by EGRET (e. g. Kanbach+93, Ryan 00) • It was unclear where, when, how the high-energy (HE) particles responsible for gamma-ray emission are accelerated • Complex flare build up (magnetic filed structures, loops and Active Region); • Magnetic fields reconnect releasing energy which accelerate particles; • Particles are trapped by magnetic field lines and interact with the solar atmosphere, producing gamma-rays; • Some of the particles have access to the open filed line and escape into interplanetary space; • They can also be accelerated by the CME shock and some of them can travel back to the sun and also produce gamma rays; Nicola Omodei – Stanford/KIPAC

Fermi as solar observatory Large Area Telescope (LAT) Observes 20% of the sky at any instant, views entire sky every 3 hrs 20 Me. V - 300 Ge. V, includes unexplored region between 10 - 100 Ge. V Gamma-ray Burst Monitor (GBM) Two type of detectors (12 Na. I and 2 BGO) Observes entire unocculted sky Detects transients from 8 ke. V - 40 Me. V Fermi's Excellent Solar Capabilities: • High-sensitivity at energy > 100 Me. V • Improved angular resolution at high energy • Broader energy range, covering interesting features of the X-ray to gamma-ray spectrum • Wide field of view, optimal for solar flares Nicola Omodei – Stanford/KIPAC

Impulsive & Long Duration flares SOL 2010 -06 -12 T 00: 57 PRELIMINARY June 12, 2010: Gamma-Ray temporally associated with impulsive hard X-ray emission. Particles accelerated up to ~ 300 Me. V in few seconds; Hard X-ray pile up in ACD causes suppression of the standard LAT event rate (on-ground classification of gamma-rays) March 7/8 2011: Sustained emission associated to one Signal recovered in LAT Low Energy Events (looser selection cut) impulsive episode in X-rays; Sustained gamma-ray emission not observed Ackermann et al. 2012, Ap. J. . . 745. . 144 A Accompanied by modest SEP, but very fast (~2000 km/s) CME; Continuous interaction of particles with the sun for hours after the impulsive flare; Nicola Omodei – Stanford/KIPAC

Let’s focus on impulsive events: SOL 2010 -0612 T 00: 57 511 ke. V e+e- 3. 3 2. 2 Me. V neutron LAT Nuclear lines <1. 2 2. 4 Me. V Pion decay GBM 3. 2 4. 3 4. 5 • Data analysis of the join GBM and LAT data provides useful information about the underlying accelerated particle distributions: – Electron Bremsstrahlung dominates at < 1 Me. V energies • Not a simple powerlaw: hardening followed by a roll-off (at 2. 4 Me. V); not compatible with transport effects alone; – Protons/ions: gamma-ray spectral features as a proxy of the accelerated ion spectrum ~2 Component Energy of gamma-ray Energy of the ions Derived accelerated ion spectrum Neutron Capture 2. 2 Me. V 10 -50 Me. V 3. 2 (10 -50 Me. V) Nuclear lines 5 -20 Me. V 50 -20 Me. V 4. 3 (50 -300 Me. V) Pions >300 Me. V >280 Me. V 4. 5 (>300 Me. V) Ackermann et al. 2012, Ap. J. . . 745. . 144 A Nicola Omodei – Stanford/KIPAC

Combined GBM and LAT timing studies GBM Ackermann et al. 2012, Ap. J. . . 745. . 144 A • High energy gamma-rays delayed by few seconds: – ~3 seconds onset and ~10 seconds delay in the peak time; – Similar “double peaked” structure in Xand Gamma- rays; • This implies: – Protons/electrons began reaching >100 Me. V energies after only few seconds after ~100 ke. V electrons; – Build-up process, lasting approximately 10 seconds; LAT Nicola Omodei – Stanford/KIPAC

High Significance Detections PRELIMINARY Date Type GOES Class CME speed 2010 -06 -12 Impulsive M-class <500 km/s 2011 -03 -07 ~15 h M-class ~2000 km/s 2011 -06 -07 ~3 h M-class ~1200 km/s 2011 -08 -04 ~3 h X-Class ~1000 km/s 2011 -08 -09 Impulsive X-Class ~1700 km/s 2011 -09 -06 Impulsive + 3 h X-Class ~1000 km/s 2011 -09 -07 ~6 h X-Class ~700 km/s 2011 -09 -24 Impulsive X-Class <500 km/s+1500 km/s (delayed) 2012 -01 -23 ~9 h M-class ~1500 km/s 2012 -01 -27 ~3 h X-Class MULTIPLE >1500 km/s 2012 -03 -05 ~6 h X-Class ~1700 km/s 2012 -03 -07 Impulsive + ~20 h X-Class MULTIPLE >1700 km/s 2012 -03 -09 ~6 h M-class ~1000 km/s 2012 -03 -10 ~3 h M-class ~1700 km/s 2012 -05 -17 ~3 h M-class ~1700 km/s Nicola Omodei – Stanford/KIPAC

Impulsive Flare detection 2010 June 12 00: 55: 06 2011 Aug 09 08: 01 Y R A N MI I L E PR 2011 Sept 06 22: 17 2011 Sept 24 09: 34: 38 Nicola Omodei – Stanford/KIPAC • > 20 Me. V events, with lose event selection (LLE); • Flare events visible ontop of the varying background (celestial and local CR); • Flare of both GOES X and M classes seen;

Long duration flares March 7/8, 2011 Solar Flare - M Class PRELIMINARY March 7, 2012 Solar Flare - X 5 & X 1 Class High energy gamma-rays (>100 Me. V) observed up to 20 hours Nicola Omodei – Stanford/KIPAC

The longest lasting gamma-ray emission: March 7, 2012 • A very bright Solar Flare was detected on March 7, exceeding: • 1000 times the flux of the steady Sun; • 100 times the flux of Vela; • 50 times the Crab flare; • High energy emission (>100 Me. V, up to 4 Ge. V) lasts for ~20 hours • Softening of the spectrum with time LAT 1 day all sky data >100 Me. V PRELIMINARY Nicola Omodei – Stanford/KIPAC

March 7, 2012 • Normally the LAT observe the sky with a different rocking angle every orbit (+50/-50) • A modified rocking profile with fixed rocking angle can also be adopted for increasing exposure Nicola Omodei – Stanford/KIPAC

On shorter time scales: the first hour X 5. 4 flare X 1 flare Enhancement of the BGO spectrum (nuclear lines) 511 ke. V e+e 2. 2 Me. V neutron PRELIMINARY Nuclear lines Orbit Sunrise Flux > 100 Me. V Pion decay Sun In the LAT Fo. V Y R A IN IM L E PR Proton index Softening of the proton spectrum Hardening of the proton spectrum: new injection of particles with the X 1 flare Nicola Omodei – Stanford/KIPAC

Localization Location computed during the first orbit ~2400 seconds of data • Events corrected for the “fisheye-effect” • 95% CL error circle with systematic error added in quadrature • Interval analyzed: first orbit ~2400 seconds of data • Location of the gamma-ray emission consistent with the location of the Active Region 11429 • Continuous acceleration of particles for ~20 hours PRELIMINARY Nicola Omodei – Stanford/KIPAC

Localization • Events corrected for the “fish(one per orbit) eye-effect” • 95% CL error circle with systematic error added in quadrature • Interval analyzed: first orbit ~2400 seconds of data • Location of the gamma-ray emission consistent with the location of the Active Region 11429 • Continuous acceleration of particles for ~20 hours PRELIMINARY • Localized gamma-ray emission consistent with the Active Region at later time Locations computed during multiple orbits Nicola Omodei – Stanford/KIPAC

Summary • Fermi LAT has detected >100 Me. V gamma-rays from solar flares, including the most energetic gamma-rays and the longest-duration emission; – – Long Lasting emission flare and Impulsive flare events detected; Joint LAT-GBM observations unveil the properties of the accelerated particles, such as spectrum and time scales of the accelerated particles; Thanks to the LAT’s improved angular resolution, we can now localize time-extended gamma-ray emission to the site of the X-ray flare for the first time; As the solar cycle progresses toward the maximum of Cycle 24 (mid-2013), the number of extreme energetic flares will increase; Nicola Omodei – Stanford/KIPAC 12

Backup Slides

Possible scenario 1 • Trap and precipitation of HE particles produced during the impulsive phase via magnetic reconnection (e. g. , Kanbach et al. 1993) ² Pitch angles of trapped particles are altered by Coloumb collisions • ² Trapping time is limited by Coulomb collision time ² The observed duration of ~12 hours require the coronal density of <1011 cm-3 (under calculation) ² Is it possible to explain the LAT rising profile? Yokoyama & Shibata 2001

Possible scenario 2 • Precipitation of HE protons accelerated stochastically within the loop (2 nd order Fermi) (e. g. , Ryan & Lee 1991) • MHD turbulence ² MHD turbulence work as a scatter, and particles are stochastically accelerated ² Assuming the loop size of 10^5 km and Alfven velocity of 1000 km/s, MHD turbulence is maintained only for ~100 s, unless there is an energizing process in flaring loops ² How the MHD turbulence is maintained? (Is it possible to explain the long-lived signature? ) SOHO EUV image © NASA

Possible scenario 3 • Return of protons accelerated by CME-driven shock (1 st order Fermi) (Murphy et al. 1987, Cliver et al. 1993) • ² Maximum energy of protons • ² Acceleration time of 1 Ge. V proton ² The fast CME-driven shock can easily and immediately accelerate protons up to >300 Me. V ² Note that the CME-driven shock proceeds away from the Sun ² Is it possible to explain the LAT rising profile? 20 Cliver+1993