observation of impulsive solar flares with the fermi large area telescope !...

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

mailto:[email protected]

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;


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


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


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


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


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



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


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


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


• 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


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


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


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


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


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

Backup Slides

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


• 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?


• Return of protons accelerated by CME-driven shock (1st order Fermi) (Murphy et al. 1987, Cliver et al. 1993)

•

•

Cliver+199320

observation of impulsive solar flares with the fermi large area telescope !...

Documents