A New View of the High-Energy γ-ray Sky with the Fermi Telescope Aurelien Bouvier KIPAC/SLAC, Stanford University On behalf of the Fermi collaboration SNOWPAC, 2010
The Fermi observatory Launch: June 11 th, 2008 Orbit: 565 km, 25.6 o inclination Observing strategy: Sky Survey Gamma-Ray Burst Monitor (GBM): 8 kev -> 40 MeV Large Area Telescope (LAT) 20 MeV -> 300 GeV FoV ~2.4 str
The Fermi sky (after 11 month) 1451 sources with TS>25 arxiv:1002.2280
Outline 1. Cosmic-ray related observations: Supernovae Remnants Large Magellanic Cloud Starburst galaxies 2. Indirect search for Dark Matter 3. Gamma-Ray Bursts
Supernovae Remnants IC443 Cas A Cloud contours W51C W44 PSF deconvolved image RX J1713.7-3946
Young SNRs Abdo et al., ApJ, 710L, 92A Cas A Cas A: Leptonic (IC+brem): B~0.1mG & W e ~10 49 ergs Hadronic (π 0 decay): W p ~3x10 49 ergs RX J1713.7-3946 PRELIMINARY RX J1713.7-3946: Complicated region; Statistics do not allow to disentangle btw IC and π 0 decay
Middle aged SNRs Interaction with molecular clouds Hadronic emission favored: IC: W e ~10 51 ergs or IRF ~ 10 x measured galactic IRF Brehmstrahlung: no break observed in radio spectrum + large W e and/or small cloud density to reduce π 0 decay emission Infered proton spectra have break around 10-50 GeV (particle escape from acceleration site?) Broadband modeling of W51C Abdo et al., ApJ, 706L, 1A
Large Magellanic Cloud Abdo et al., ApJ, 512A, 7A Spatially extended source (>4σ): Little correlation with neutral gas Best spatial correlation with ionized hydrogen template Spectrum consistent with π 0 decay Bright γ-ray emission in 30 Doradus Small GeV proton diffusion length Bremsstrahlung Inverse Compton π 0 decay Average cosmic-ray density ~20-30% that of solar vicinity (consistent with difference in galactic and LMC SN rate)
Starburst galaxies: M82 & NGC 253 Abdo et al., ApJ, 709L, 152A New class of γ-ray sources M82 (6.8σ) detected by Veritas NGC 253 (4.8σ) detected by HESS Spectra consistent with models of diffuse galactic γ-ray emission although weakly constrained spectral shapes Enhanced CR intensity required to explain the observed flux γ-ray luminosity seem to correlate with [SN_rate] x [G as mass]
Dark Matter: search for WIMP signature Satellites: Low background and good source ID, but low statistics Galactic center: Good statistics but source confusion/diffuse background Milky Way halo: Large statistics but diffuse background All-sky map of gamma rays from DM annihilation arxiv:0908.0195 (based on Via Lactea II simulation) And electrons! Spectral lines: No astrophysical uncertainties, good source ID, but low statistics dsph & Clusters: Low background but low statistics Extragalactic: Large statistics, but astrophysics, galactic diffuse background
Search for spectral lines Search in B>10 and 20 x20 around galactic center No astrophysical uncertainties -> Smoking gun signal for DM BUT: signal might be faint LAT energy resolution is the limitation (~10% at 100 GeV) No line detection so far Upper-limits on cross-section constrain theories with nonthermally produced WIMPs arxiv:1001.4836
CR electron spectrum Not compatible with the pre-fermi data diffusive CR model No evidence of a prominent spectral feature Abdo et al., PRL, 102r1101A Possible interpretations: revised diffusion model or extra component (astrophysical or DM) DM contribution is not required, however cannot be ruled out
Gamma-Ray Bursts GBM: ~250 GRBs/year LAT: ~10 GRBs/year HE delayed emission common feature of LAT bursts difficulty for leptonic models time to accelerate protons and develop cascade? Abdo et al., Science 323, 1688C GRB 080916C
HE GRB spectra Abdo et al., ApJ 706L, 138A GRB 090902B Additional component extending down to 10 kev: difficulty for IC/SSC models Difficulty for hadronic models: Hard to reproduce the observed correlated variability at low and high energy E iso ~ 100-1000 x E γ GRB 090926A: spectral break (>5σ) at ~1 GeV not possible to distinguish shape of the break If cutoff due to γ-γ absorption, 1 st direct measurement of bulk lorentz factor: Γ~630 PRELIMINARY GRB 090926A
Lorentz invariance (LIV) 31 GeV photon associated with GRB 090510 (z~0.9) Some Quantum Gravity models predict an energy dependent velocity of light Conservative assumption: 31 GeV photon emitted sometime after low energy onset: M QG > 1.19 x M Plank Models with linear LIV are disfavored Abdo et al., Nature, 462, 331
Electron spectrum LMC GRBs Starburst galaxies SNRs
Backup
dsph galaxies & clusters arxiv:1001.4531 arxiv:1002.2239 Exclusion region cutting into interesting parameter space for some WIMP models Results for Clusters are strongly dependent on substructure assumption
W28 - press release HE CRs could escape the shock front and interact further away with molecular clouds Possibility: highest energy CRs escape first and have larger diffusion coefficient so region A is seen in TeV but not in GeV