interaction of cosmic-rays with the solar system bodies as seen by fermi lat monica brigida bari...
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Interaction of Cosmic-Rays with Interaction of Cosmic-Rays with the Solar System Bodies as the Solar System Bodies as
seen by Fermi LATseen by Fermi LAT
Monica Brigida
Bari University
For the Fermi LAT Collaboration
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Sources in the Solar SystemSources in the Solar System
Sources:• The Moon • The Sun (quiet and/or flaring)• The Earth
Potential SourcesAsteroids in different populations:
Main Asteroid Belt (MBAs)Jovian and Neptunian Trojans (Trojans)Kuiper Belt Objects (KBOs)
Other planetsDebris (< few meter size, dust, grains) MBAs, Trojans,
KBOs Oort Cloud
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Non flaring Sources in the Solar SystemNon flaring Sources in the Solar System
• Non flaring sources in the Solar System are bright in gamma rays due to their interaction with Galactic cosmic rays (CR)
• Moon gamma ray emission depends on the flux of CR nuclei near its surface
• Quiet solar gamma ray emission has two components: IC due to the CR electron scattering off solar photons in the heliosphere and the CR nuclei interactions with the solar atmosphere
• Gamma ray emission studies are a sensible probe for CR fluxes in the solar system
• Gamma ray flux measurements depends on the solar cycle
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Solar activity and Cosmic raysSolar activity and Cosmic rays
Max solar activity ‐> min cosmic‐ray flux
Min solar activity ‐> max cosmic‐ray flux
The gamma‐ray flux depends on CRs flux intensities
‐ Solar Activity is now increasing from its minimum
‐ Solar Activity expected to peak around 2012
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Emission ModelsEmission Models
“γ-ray emission” due to CR interactions with surface material: Moon rock (solid) Solar atmosphere (gaseous)
Lunar ᵞ-ray emission: Decay of neutral pions and Kaons,
bremsstrahlung by electrons and
Compton scattering of secondary photons
Similar emission mechanism for any solid object in Solar System
CR γ
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Gamma rays from the MoonGamma rays from the Moon
soft gamma rays ‐> coming from thecentral part of the lunar disk
high gamma rays ‐> likely produced byCRs hitting the lunar surface with analmost tangential trajectory (the lunardisk limb).
EGRET detected the Moon(Thompson ‘97)Flux(>100MeV) = 4.5x10-7 cm-2s-1
Moskalenko&Porter ’07
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Quiet Solar emission: pion decayQuiet Solar emission: pion decay
• Solar disk emission due to interactions of CR particles with solar atmosphere (Seckel ’91)
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CR γSeckel ‘91
This component is therefore localized in the solar disk (almost pointlike)
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Sun: second component Sun: second component Inverse Compton ScatteringInverse Compton Scattering
©UCAR
Inverse-Compton scattering of solar photons in the heliosphere by Galactic CR electrons: the emission is predicted extended •Electrons are isotropic•Photons have a radial angular profile
e
Moskalenko ’06Orlando&Strong’08
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Detection of the Sun with EGRETDetection of the Sun with EGRET
‐ In agreement with theoretical models of IC and disk‐ Detection of both IC and disk, but low statystics
Orlando & Strong
F_IC(>100MeV) =(3.8+/-2.2)x10-7 cm-2s-1
In 10 degrees radiusF_disk(>100MeV) = (1.8+/-1.1)x10-7 cm-2s-1
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Fermi Data SelectionFermi Data Selection
• Data from Aug 4, 2008 until February 4, 2010• Analysis in celestial relative coordinates
• SUN is moving about 1°/day • MOON is moving about 15°/day
ꄴ (Moon and Sun centered data)• E > 100MeV• Zenith angle < 105°
• Galactic Plane Cut (>30°)• Moon-Sun angular separation >20°• ROI: 20°
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Background DeterminationBackground Determination
The “fake” source method: A fake source follow the path of the real source but 30 degrees
away (passes through the same areas on the sky but at different times)
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Fermi: the Sun track in the skyFermi: the Sun track in the sky
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The Sun ObservationThe Sun Observation
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Sun Centered dataCompared with the background• fakesun •AllSky simulation (i.e. taking into accout all 1FGL sources and the diffuse component)
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The Sun Spectrum: the disk componentThe Sun Spectrum: the disk component
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Flux(>100MeV)=(4.86 ± 0.14(stat) ± 0.97(syst)) x 10-7 cm-2 s-1
Point component modeled with a PL2, taking into account the PSF
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Angular profiles: evidence of extended Angular profiles: evidence of extended emissionemission
Missing extended component
Good description of the background
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- Data- BKG- BKG+point source- Disk Component- IC Component- BKG+IC+point
Angular profiles:Angular profiles: evidence of extended emission E>100MeV evidence of extended emission E>100MeV
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Results: the IC componentResults: the IC component
Maximun Likelihood fit results:
IC Flux(>100MeV)=(5.66 ± 0.61(stat)±2.26(syst))x10-7 cm-2 s-1
IC Model with different solar modulation, based on the electron spectrum measured by Fermi/LAT above 7 GeV (Abdo et al. 2010)
Inverse Compton spectrum from within 16 deg from the Sun
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PR
ELIM
INA
RY
Moon Observation and SpectrumMoon Observation and Spectrum
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PRELI
MIN
ARY
PRELIMIARY
18
PRELIMINARY
F (>100MeV) = (1.21 ± 0.02 stat ± 0.2 syst) × 10‐6 cm‐2s‐1
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The brightest The brightest γγ-ray source on the sky: the Earth -ray source on the sky: the Earth
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• Earth’s gamma-ray emission from CR interactions in the atmosphere• Expect a power-law from the limb above ~5 GeV following the CR spectrum
• Earth’s gamma-ray emission from CR interactions in the atmosphere• Expect a power-law from the limb above ~5 GeV following the CR spectrum
Earth emission observations and energy responseEarth emission observations and energy response
intensity maps
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Gamma rays from small Gamma rays from small solar system bodiessolar system bodies
To probe the interstellar spectrum of CR protons (Moskalenko&Porter ’08)
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ConclusionsConclusions
• With the Fermi/LAT we observed the gamma ray emission from the Earth, the Moon and the Sun
• Continuous monitoring of the gamma‐ray sources for the solar cycle 24th will bring information on CR propagation in the heliosphere and across the inner Solar System
• Paper on the Moon and the Sun will BE SUBMITTED SOON!
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