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Observation of impulsive Solar Observation of impulsive Solar Flares with the Fermi Large Flares with the Fermi Large
Area TelescopeArea Telescope
!!
[email protected] LAT and GBM Collaborations
Nicola Omodei – Stanford/KIPAC
Gamma-ray emission from the SunGamma-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 GeV) 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, Ryan00)• 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 observatoryFermi as solar observatory
Large Area Telescope (LAT)Observes 20% of the sky at any instant, views entire sky every 3 hrs20 MeV - 300 GeV, includes unexplored region between 10 - 100 GeV
Gamma-ray Burst Monitor (GBM)Two type of detectors (12 NaI and 2 BGO) Observes entire unocculted skyDetects transients from 8 keV - 40 MeV
Fermi's Excellent Solar Capabilities:•High-sensitivity at energy > 100 MeV•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 flaresImpulsive & Long Duration flares
June 12, 2010: Gamma-Ray temporally associated with impulsive hard X-ray emission. Particles accelerated up to ~ 300 MeV in few seconds;Hard X-ray pile up in ACD causes suppression of the standard LAT event rate (on-ground classification of gamma-rays)Signal recovered in LAT Low Energy Events (looser selection cut)Sustained gamma-ray emission not observed
Ackermann et al. 2012, ApJ...745..144A
March7/8 2011: Sustained emission associated to one impulsive episode in X-rays;Accompanied by modest SEP, but very fast (~2000 km/s) CME;Continuous interaction of particles with the sun for hours after the impulsive flare;
PRELIMINARYSOL2010-06-12T00:57
Nicola Omodei – Stanford/KIPAC
Let’s focus on impulsive events: SOL2010-06-Let’s focus on impulsive events: SOL2010-06-12T00:5712T00:57
• Data analysis of the join GBM and LAT data provides useful information about the underlying accelerated particle distributions:– Electron Bremsstrahlung
dominates at < 1 MeV energies• Not a simple powerlaw:
hardening followed by a roll-off (at 2.4 MeV); not compatible with transport effects alone;
– Protons/ions: gamma-ray spectral features as a proxy of the accelerated ion spectrum
GBM
LAT
Ackermann et al. 2012, ApJ...745..144A
2.2 MeV neutron
Nuclear lines
511 keV e+e-
Pion decay
3.3
<1.2
2.4 MeV
3.2 4.3
Component Energy of gamma-ray
Energy of the ions
Derived accelerated ion spectrum
Neutron Capture 2.2 MeV 10-50 MeV 3.2 (10-50 MeV)
Nuclear lines 5-20 MeV 50-20 MeV 4.3 (50 -300 MeV)
Pions >300 MeV >280 MeV 4.5 (>300 MeV)
4.5
~2
Nicola Omodei – Stanford/KIPAC
Combined GBM and LAT timing studiesCombined GBM and LAT timing studies
• High energy gamma-rays delayed by few seconds:
– ~3 seconds onset and ~10 seconds delay in the peak time;
– Similar “double peaked” structure in X- and Gamma- rays;
• This implies:– Protons/electrons began reaching
>100 MeV energies after only few seconds after ~100 keV electrons;
– Build-up process, lasting approximately 10 seconds;
GBM LAT
Ackermann et al. 2012, ApJ...745..144A
Nicola Omodei – Stanford/KIPAC
High Significance DetectionsHigh Significance Detections
Date Type GOES Class CME speed
2010-06-12 Impulsive M-class <500 km/s
2011-03-07 ~15h M-class ~2000 km/s
2011-06-07 ~3h M-class ~1200 km/s
2011-08-04 ~3h X-Class ~1000 km/s
2011-08-09 Impulsive X-Class ~1700 km/s
2011-09-06 Impulsive + 3h X-Class ~1000 km/s
2011-09-07 ~6h X-Class ~700 km/s
2011-09-24 Impulsive X-Class<500 km/s+1500 km/s (delayed)
2012-01-23 ~9h M-class ~1500 km/s
2012-01-27 ~3h X-Class MULTIPLE >1500 km/s
2012-03-05 ~6h X-Class ~1700 km/s
2012-03-07 Impulsive + ~20 h X-Class MULTIPLE >1700 km/s
2012-03-09 ~6h M-class ~1000 km/s
2012-03-10 ~3h M-class ~1700 km/s
2012-05-17 ~3h M-class ~1700 km/s
PRELIMINARY
Nicola Omodei – Stanford/KIPAC
Impulsive Flare detectionImpulsive Flare detection
• > 20 MeV events, with lose event selection (LLE);
• Flare events visible on-top of the varying background (celestial and local CR);
• Flare of both GOES X and M classes seen;
2011 Aug 09 08:01:01
2010 June 12 00:55:06
2011 Sept 06 22:17:17
2011 Sept 24 09:34:38
PRELIMIN
ARY
Nicola Omodei – Stanford/KIPAC
Long duration flaresLong duration flares
March 7/8, 2011 Solar Flare - M Class
March 7, 2012 Solar Flare - X5 & X1 Class
High energy gamma-rays (>100 MeV) observed up to 20 hours
PRELIMINARY
Nicola Omodei – Stanford/KIPAC
• 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 MeV, up to 4 GeV)
lasts for ~20 hours• Softening of the spectrum with time
The longest lasting gamma-ray emission:The longest lasting gamma-ray emission: March 7, 2012 March 7, 2012
PRELIMINARYLAT 1 day all sky data >100 MeV
Nicola Omodei – Stanford/KIPAC
March 7, 2012March 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 hourOn shorter time scales: the first hour
Orbit Sunrise
X5.4 flareX1 flare
PRELIMINARY
Hardening of the proton spectrum: new injection of particles with the X1 flare
Enhancement of the BGO spectrum (nuclear lines)
2.2 MeV neutron
Nuclear lines
511 keV e+e-
PRELIMINARY
Pion decay
Sun In the LAT FoV
Softening of the proton spectrum
Flux > 100 MeV
Proton index
Nicola Omodei – Stanford/KIPAC
Location computed during the first orbit
~2400 seconds of data
LocalizationLocalization
• Events corrected for the “fish-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
Nicola Omodei – Stanford/KIPAC
LocalizationLocalization
• Events corrected for the “fish-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
• Localized gamma-ray emission consistent with the Active Region at later time
Locations computed during multiple orbits
(one per orbit)
PRELIMINARY
Nicola Omodei – Stanford/KIPAC
SummarySummary
• Fermi LAT has detected >100 MeV 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;
12
Possible scenario 1Possible scenario 1
• Trap and precipitation of HE particles produced during the impulsive phase via magnetic reconnection (e.g., Kanbach et al. 1993)
•
Pitch angles of trapped particles are altered by Coloumb collisions
Trapping time is limited by Coulomb collision time
The observed duration of ~12 hours require the coronal density of <1011 cm-3 (under calculation)
Is it possible to explain the LAT rising profile?
Yokoyama & Shibata 2001
Possible scenario 2Possible scenario 2
• Precipitation of HE protons accelerated stochastically within the loop (2nd order Fermi) (e.g., Ryan & Lee 1991)
•
MHD turbulence work as a scatter, and particles are stochastically accelerated
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
How the MHD turbulence is maintained? (Is it possible to explain the long-lived signature?)
SOHO EUV image © NASA
MHD turbulence
Maximum energy of protons
Acceleration time of 1 GeV proton
The fast CME-driven shock can easily and immediately accelerate protons up to >300 MeV
Note that the CME-driven shock proceeds away from the Sun
Is it possible to explain the LAT rising profile?
Possible scenario 3Possible scenario 3
• Return of protons accelerated by CME-driven shock (1st order Fermi) (Murphy et al. 1987, Cliver et al. 1993)
•
•
Cliver+199320