A New View of the High-Energy γ-ray Sky with the Fermi Telescope

Transcription

1 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

2 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

3 The Fermi sky (after 11 month) 1451 sources with TS>25 arxiv:

4 Outline 1. Cosmic-ray related observations: Supernovae Remnants Large Magellanic Cloud Starburst galaxies 2. Indirect search for Dark Matter 3. Gamma-Ray Bursts

5 Supernovae Remnants IC443 Cas A Cloud contours W51C W44 PSF deconvolved image RX J

6 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 J PRELIMINARY RX J : Complicated region; Statistics do not allow to disentangle btw IC and π 0 decay

7 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 GeV (particle escape from acceleration site?) Broadband modeling of W51C Abdo et al., ApJ, 706L, 1A

8 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)

9 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]

10 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: (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

11 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:

12 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

13 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 C

14 HE GRB spectra Abdo et al., ApJ 706L, 138A GRB B 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 ~ x E γ GRB A: 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 A

15 Lorentz invariance (LIV) 31 GeV photon associated with GRB (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

16 Electron spectrum LMC GRBs Starburst galaxies SNRs

17 Backup

18 dsph galaxies & clusters arxiv: arxiv: Exclusion region cutting into interesting parameter space for some WIMP models Results for Clusters are strongly dependent on substructure assumption

19 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