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
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
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
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
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)
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
Angular profiles: evidence of extended Angular profiles: evidence of extended emissionemission
Missing extended component
Good description of the background
- 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
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
PR
ELIM
INA
RY
Moon Observation and SpectrumMoon Observation and Spectrum
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PRELI
MIN
ARY
PRELIMIARY
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PRELIMINARY
F (>100MeV) = (1.21 ± 0.02 stat ± 0.2 syst) × 10‐6 cm‐2s‐1
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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