Fermi: Fermi: Highlights of Highlights of GeV Gamma-ray GeV Gamma-ray Astronomy Astronomy Dave Thompson Dave Thompson NASA GSFC NASA GSFC On behalf of the Fermi Gamma-ray On behalf of the Fermi Gamma-ray Space Telescope Large Area Space Telescope Large Area Telescope Collaboration Telescope Collaboration Neutrino Oscillation Workshop Otranto, Lecce, Italy September, 2010
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Fermi: Highlights of GeV Gamma-ray Astronomy Dave Thompson NASA GSFC On behalf of the Fermi Gamma-ray Space Telescope Large Area Telescope Collaboration.
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Fermi: Highlights of Fermi: Highlights of GeV Gamma-ray GeV Gamma-ray AstronomyAstronomy
Dave ThompsonDave ThompsonNASA GSFCNASA GSFC
On behalf of the Fermi Gamma-ray Space On behalf of the Fermi Gamma-ray Space Telescope Large Area Telescope Telescope Large Area Telescope CollaborationCollaboration
– High-energy gamma rays are primarily produced by interactions of energetic particles.
• Typical processes are inelastic nuclear collisions (pion production) and inverse Compton scattering.
• Gamma rays tracing hadronic processes are of particular interest for neutrino observations.
• Neutrino observations may be critical to learning the nature of gamma-ray sources.
– The Universe is mainly transparent to gamma rays with energies less than 20 GeV, so they can probe distant or obscured regions.
• Potential to identify locations and time variability for neutrino-producing objects.
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The Fermi Gamma-ray Space Telescope The Fermi Gamma-ray Space Telescope An International MissionAn International Mission
Gamma-ray Burst Monitor (GBM)
NaI and BGO Detectors8 keV - 40 MeV
Large Area Telescope (LAT)
Spacecraft Partner: General Dynamics
KEY FEATURES• 20 MeV -> >300 GeV• 2.4 Steradian field of view• Operated in scanning mode, so views the entire sky every 3 hours.• Peak effective area ~8000 cm2
• Single photon angular resolution 0.8o at 1 GeV, better at higher energies.• Source location capability 1-10 arcmin.• Energy resolution 10-20%
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The Gamma-ray Sky Seen with Fermi LAT
Sources are seen against a strong diffuse background. E > 1 GeV image.
Galactic diffuse emission comes from cosmic-ray interactions with the interstellar medium
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Gamma-ray Spectrum at Intermediate Galactic Latitudes
Observed
Total with Sources
Bremsstrahlung
Sources
Total Diffuse
Isotropic
Inverse Compton
These pion-producing interactions imply that there is a diffuse background of neutrinos, too.
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1451 Sources
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Extragalactic Gamma-ray
Sources
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• Both long (>2 sec) and short (<2 sec) bursts have been seen
• Some bursts show high-energy emission afterglow
• Constraint: lower limit of bulk Lorentz factor: Γmin ~1000
• Some bursts have an extra spectral component compared to the standard Band model.
• These short, bright flashes can be used as tools to probe basic physics, as in the example here.
Gamma-ray Bursts (GRBs) - the Brightest and Gamma-ray Bursts (GRBs) - the Brightest and Most Distant Sources Seen by FermiMost Distant Sources Seen by Fermi
Constraints on the quantum gravity mass scale (MQG) by direct measurement of photon arrival times, testing Lorentz invariance violation.
MQG,1/MPlanck > 1.19
Abdo et al. 2009, Nature 462, 331GRB 090510
31 GeV
GBM NaI
GBM BGO
LAT (>1MeV)
0.83 s
Collapsar: Rapidly spinning stellar core collapse supernova, with relativistic jets that can produce long GRBs
Compact Merger: Two neutron stars, or a neutron star and a black hole, merge, producing a jet that gives rise to a short GRB
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Over half the bright sources seen with LAT appear to be associated with Active Galactic Nuclei (AGN)
• Power comes from material falling toward a supermassive black hole
• Some of this energy fuels a jet of high-energy particles that travel at nearly the speed of light
• Fermi LAT sees primarily blazars, for which the jet is pointed toward Earth.
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The Variable Gamma-ray Sky
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Blazar PKS 1502+106Blazar PKS 1502+106
The spectral Energy Distribution (SED) of this blazar is complex, requiring multiple components that vary with time. A key result for Fermi and multiwavelength studies: in most cases, simple models for blazars are inadequate. In some models of blazar jets, hadrons transport much of the energy and have neutrino-producing interactions. Seeing neutrinos from a blazar would be the key to verifying hadronic interactions.
Gamma rays
Ultraviolet
X-rays
Optical
Radio
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Centaurus A - Radio GalaxyCentaurus A - Radio Galaxy
LAT counts map with background (isotropic and diffuse) and field point sources subtracted
WMAP image provided by Nils Odegard (GSFC)
Over ½ of the total >100 MeV observed LAT flux in the lobes
Requires 0.1-1 TeV electrons in giant ‘relic’ lobes: accelerated in-situ or efficient energy transport from the center of the galaxy.
LAT PSF
E > 200 MeV 22 GHz
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Large Magellanic Cloud
GeV gamma rays in these galaxies come primarily from the interactions of cosmic ray hadrons and electrons with interstellar matter and photon fields.
Galaxies Dominated by Cosmic-Ray Galaxies Dominated by Cosmic-Ray InteractionsInteractions
A Surprise - A Gamma-ray NovaA Surprise - A Gamma-ray Nova
• In early March, the LAT skywatchers found a new, flaring gamma-ray source in the Cygnus region.
• To our surprise, we learned that an optical flare of the symbiotic system V407 Cyg (red giant/white dwarf binary) had occurred at about the same time.
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A Surprise - A Gamma-ray NovaA Surprise - A Gamma-ray Nova
The energy spectrum of the nova is plausibly produced by accelerated protons from the expanding shell of the nova colliding with the wind from the red giant star.
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What Next for Fermi?What Next for Fermi?• As we start the third year of operations, we have only
scratched the surface of what the Fermi Gamma-ray Space Telescope can do.– The gamma-ray sky is changing every day, so
there is always something new to learn about the extreme Universe.
• Beyond pulsars, blazars, X-ray binaries, SNR, starburst galaxies and gamma-ray bursts, other sources remain mysteries. Nearly 40% of the sources in the First LAT Catalog do not seem to have obvious counterparts at other wavelengths. – Multiwavelength/multimessenger studies,
including neutrino observations, will be critical for learning the nature of such sources.
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Dark-matter particles annihilate with one
another, leading to gamma rays
Light dark-matter particles produce 511 keV (low-energy)
gamma rays
WIMP dark-matter particles (neutralinos) produce 30 MeV to 10 GeV (medium-energy) gamma rays
Heavy dark-matter particles produce 300 to 600 GeV (high-energy) gamma
rays
Illustrations by Gregg Dinderman/Sky & Telescope
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Dark Matter Searches Dark Matter Searches
Dwarf Spheroidal Galaxies are known to be dominated by Dark Matter.
Upper limits on Dark Matter annihilation cross section.
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Summary
Gamma rays seen with the Fermi Gamma-ray Space Telescope are revealing sites of particle acceleration and interaction, ranging from distant Gamma-ray bursts and Active Galactic Nuclei to sources in our Galaxy.
Gamma-ray bursts, flares from Active Galactic Nuclei, Starburst Galaxies, Supernova Remnants, and Novae are all good candidates for astrophysical neutrino sources.
All the Fermi gamma-ray data are public. The Fermi Science Support Center, at http://fermi.gsfc.nasa.gov/ssc/ is