Fermi Large Area Telescope observations of high-energy gamma-ray - PowerPoint PPT Presentation

Fermi Large Area Telescope observations of high-energy gamma-ray emission from solar flares Melissa Pesce-Rollins INFN–Pisa melissa.pesce.rollins@pi.infn.it on behalf of the Fermi -LAT collaboration TeVPa/IDM June 23, 2014

The Fermi Space Telescope Gamma-ray Burst Monitor (GBM) ◮ 12 NaI and 2 BGO detectors ◮ Energy range: 8 keV–40 MeV ◮ Observes entire unocculted sky The Large Area Telescope (LAT) ◮ Pair conversion telescope ◮ Energy range: 20 MeV– > 300 GeV ◮ Large field of view ( ≈ 2 . 4 sr): 20% of the sky at any time, all parts of the sky for 30 minutes every 3 hours ◮ Observes the Sun for ∼ 20 – 40 min every 3 hours M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 2 / 18

Gamma-ray Solar flares γ -ray emission from Solar flares Produced by interactions of high-energy particles with ambient plasma: 1. Bremsstrahlung ◮ 10 keV – 1 GeV 2. Nuclear de-excitation ◮ ≈ 0.5 – 8 MeV 3. Pion decay ◮ > 10 MeV ◮ Magnetic reconnection believed to be at the origin of particle acceleration in Solar flares ◮ γ -rays provide clues on the properties of the acceleration mechanisms and information on ambient plasma ◮ Chromospheric ion abundances ◮ Maximum energy of the accelerated charged particles ◮ Coronal trapping times M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 3 / 18

Why study Solar flares with Fermi ? 45 Number of Solar flares GOES spacecraft Classification 40 detection) Classification Peak flux at 100-800 pm 35 (Watts m − 2 ) 30 Total number of >25 MeV < 10 − 7 A σ Solar flare detections 25 Fermi-LAT (>5 10 7 –10 6 B 20 10 6 –10 5 C 15 10 5 –10 4 M 10 4 –10 3 10 X 5 GRS/SMM EGRET/CGRO 0 1980 1985 1990 1995 2000 2005 2010 Year ◮ Only 9 Solar flares have been detected with E > 25 MeV prior to the launch of Fermi ◮ All of which were classified as GOES X class flares ◮ Fermi has detected more than 40 Solar flares with E > 25 MeV in first 6 years of mission ◮ More than half are classified as GOES M class flares M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 4 / 18

Why study Solar flares with Fermi ? 45 Number of Solar flares GOES spacecraft Classification 40 detection) Classification Peak flux at 100-800 pm 35 (Watts m − 2 ) 30 Total number of >25 MeV < 10 − 7 A σ Solar flare detections 25 Fermi-LAT (>5 10 7 –10 6 B 20 10 6 –10 5 C 15 10 5 –10 4 M 10 4 –10 3 10 X 5 GRS/SMM EGRET/CGRO 0 1980 1985 1990 1995 2000 2005 2010 Year ◮ Only 9 Solar flares have been detected with E > 25 MeV prior to the launch of Fermi ◮ All of which were classified as GOES X class flares ◮ Fermi has detected more than 40 Solar flares with E > 25 MeV in first 6 years of mission ◮ More than half are classified as GOES M class flares ◮ Sampling a wider range of Solar flares providing a new piece to the puzzle of the acceleration mechanisms at work M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 4 / 18

Fermi LAT as a solar observatory The LAT standard analysis ◮ Likelihood fit of spatial and spectral model of region around sun ◮ Event classification (photon v. bkg) on event-by-event basis ◮ Use classification trees to reject bkg and give high-quality photon data ◮ High flux of hard x-rays during solar flares causes pile-up in the ACD ◮ High probability of mis-classifying good photons as background The LAT Low Energy (LLE) analysis ◮ Useful only for short transients (10s of minutes or less) ◮ Model the background by fitting time series of LAT events from region around sun ◮ Relaxed event classification gives high effective area but lower signal to noise ◮ Immune to the pile-up effect in the ACD! M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 5 / 18

Impulsive flares: SOL2010-06-12T00:57 LAT ◮ Narrow and broad nuclear line emission detected by GBM ◮ Protons and ions accelerated Pion decay above ∼ 30 MeV GBM ◮ Emission up to ∼ 400 MeV detected by LAT ◮ What physical process? ◮ Fit GBM and LAT to investigate the origin ◮ Pion decay radiation electron ◮ Bremsstrahlung from bremsstrahlung power-law electron spectrum Parameter Value Power-law index (blue) 3.31 Power-law with exp cutoff (cyan) ≤ 1.2 2.4 ± 0.8 MeV Pion decay (top panel) -4.5 Power-law at 30 MeV 1.9 ± 0.2 Ackermann et al. 2012ApJ...745..144A M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 6 / 18

Timing gamma-rays and Hard X-rays: SOL2010-06-12T00:57 1.2 ◮ Electron dominated GBM/BGO GBM/BGO (100-500 keV) 0 Backround Subtracted Counts 1 LLE (>30MeV) 100–500 keV counting rates at 0.8 320 sec resolution 0.6 ◮ LAT LLE > 30 MeV at 3 second 0.4 0.2 resolution 0 ◮ LLE profile is delayed relative to -0.2 HXR profile 00:55:30 00:55:40 00:55:50 00:56:00 00:56:10 00:56:20 00:56:30 Time (UT, 2010-06-12) ◮ Weak evidence for double-peaked profile Implications of time profiles ◮ From a cross correlation ◮ protons and/or electrons reach E > 100 MeV analysis we find > 30 MeV w/in few seconds of the time it takes electrons to reach 100’s of keV emission lags the ◮ Acceleration time scales of > 100 MeV bremsstrahlung by 6 ± 3 seconds particles is similar to 100’s of keV electrons, but delayed by ≈ 10 sec M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 7 / 18

Sustained emission: SOL2012-03-07 Ajello et al. 2014ApJ...789..20 10 -2 10 5 Protons (30-50 MeV) X-ray (3-25 keV) GOES average proton flux Protons (50-100 MeV) 10 -3 X-ray (1.5-12 keV) 10 4 ◮ Fermi -LAT detected GOES X-ray [W m − 2 ] Protons (>100 MeV) [cm − 2 s − 1 sr − 1 ] 10 3 10 -4 > 100 MeV emission for 10 2 10 -5 10 1 10 -6 more than 20 hours 10 0 10 -7 10 -1 ◮ Including the most energetic 10 -8 02:00 05:00 08:00 11:00 14:00 17:00 20:00 23:00 > 100 MeV flux, LLE 10 -6 γ -ray flux [erg cm − 2 s − 1 ] > 100 MeV flux, Likelihood 2 photon (4.5 GeV) ever Proton index, LLE Proton index s Proton index, Likelihood 10 -7 Proton index, GOES HR p 3 detected during a flaring 10 -8 4 episode 10 -9 5 10 -10 02:00 05:00 08:00 11:00 14:00 17:00 20:00 23:00 2012-03-07, UT 10 -6 c) π 0 , π ± decay Power law Cut-off Power law ◮ High-energy gamma-ray spectrum is curved, 10 -7 E 2 dN/dE [erg cm − 2 s − 1 ] consistent with: 10 -8 -2 ∆log( L ) 10 ◮ Pion decay spectrum, or 8 6 10 -9 4 ◮ Electron spectrum with cutoff 2 0 4.0 4.2 4.4 4.6 4.8 5.0 5.2 Proton Spectral Index 10 -10 10 2 10 3 10 4 Energy [MeV] M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 8 / 18

Localizing the high energy gamma-rays SOL2012-03-07 ◮ Localization studies provide insight to the source of the accelerated particles ◮ We measure the direction of the emission centroid via a likelihood analysis ◮ For the brightest flares we find the > 100 MeV emission centroid to be consistent with location of the active region on the solar disk Ajello et al. 2014ApJ...789..20 M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 9 / 18

How to explain the long duration > 100 MeV emission? ◮ Coronal Mass Ejection-driven shock ◮ Continuous acceleration at flare (Murphy et al. 1987) can accelerate reconnection region via Stochastic particles acceleration (Petrosian & Liu 2004) ◮ γ emission cannot occur at CME site ◮ Accelerated particle spectra become (density too low) softer as turbulence weakens. ◮ Particles must travel back to the Sun ◮ Can explain the spectral evolution seen ◮ Could explain long lasting emission for SOL2012-03-07 M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 10 / 18

Complementary EUV and HXR data SDO/AIA ◮ M1.5 GOES class flare erupted STEREO B at 7:01:00 UT ◮ EUV and HXR data reveal that the active region is ∼ 8 ◦ behind the visible Solar limb at the time of the flare ◮ HXR footpoints were occulted during RHESSI coverage M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 11 / 18

First > 100 MeV behind the limb flare ◮ Surprising > 100 MeV emission ) -2 Flux (Watt m GOES X-ray detected by Fermi -LAT from 7:10 -6 10 UT for ∼ 30 min ◮ Including a ∼ 3 GeV photon 1.0 - 8.0 Å 10 -9 0.5 - 4.0 Å ◮ LAT emission centroid coincides 10 ) 07:00 07:30 08:00 -1 Count rate (ph s 40 with the flaring region location STEREO B 304 Å ◮ How to explain this LAT detection? 195 Å 20 ◮ γ ’s produced in the Corona or 0 ) 07:00 07:30 08:00 photosphere? -1 3 10 s -1 Count rate (cnts det RHESSI RHESSI night ← → 2 10 3-6 keV 10 6-12 keV 12-25 keV 25-50 keV ) 07:00 07:30 08:00 -1 -3 s 10 -2 PRELIMINARY Flux (ph cm >100 MeV Fermi LAT LAT upper limit Quiescent Sun [3] Fermi night Paper in preparation ← → -6 10 07:00 07:30 08:00 2013/10/11 (UT) M. Pesce-Rollins (INFN) TeVPa/IDM June 23, 2014 12 / 18