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Sources of GeV Photons and the Fermi Results

Chuck Dermer, NRL http://heseweb.nrl.navy.mil/gamma/~dermer/default.htm. Sources of GeV Photons and the Fermi Results. Posted by next Thursday or Friday. With acknowledgments!. 1. GeV instrumentation and the GeV sky with the Fermi Gamma-ray Space Telescope

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Sources of GeV Photons and the Fermi Results

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  1. Chuck Dermer, NRL http://heseweb.nrl.navy.mil/gamma/~dermer/default.htm Sources of GeV Photons and the Fermi Results Posted by next Thursday or Friday With acknowledgments! 1. GeV instrumentation and the GeV sky with the Fermi Gamma-ray Space Telescope 2. First Fermi Catalog of Gamma Ray Sources and the Fermi Pulsar Catalog 3.First Fermi AGN Catalog 4. Relativistic jet physics and blazars 5. g rays from cosmic rays in the Galaxy 6. g rays from star-forming galaxies and clusters of galaxies, and the diffuse extragalactic g-ray background 7. Microquasars, radio galaxies, and the extragalactic background light 8. Fermi Observations of Gamma Ray Bursts 9. Fermi acceleration, ultra-high energy cosmic rays, and Fermi Dermer Saas-Fee Lecture 6 15-20 March 2010

  2. Outline • Fermi detection of the LMC and SMC • GeV-TeV Emission from Normal and Starburst Galaxies • Search for Gamma-ray Emission from Clusters of Galaxies • Estimate of diffuse g-ray background from star-forming galaxies and clusters of galaxies • Fermi measurements of unresolved/diffuse extragalactic g-ray background Thanks to J. Knödlseder, K. Bechtol,Pierrick Martin,M. Ackermann Dermer Saas-Fee Lecture 6 15-20 March 2010

  3. Normal, Starburst and IR Luminous Galaxies Spitzer • Detection of LMC with EGRET • fg= 19  10-8 ph(>100 MeV) cm-2 s-1 • (Sreekumar et al.1992) • Spectral shape consistent with that • expected from cosmic ray interactions • with matter • Scale Milky Way and LMC to • local galaxies (SMC, M31) • starburst Galaxies (M82, NGC 253;  3 Mpc) • IR Luminous Galaxies (Arp 220;  72 Mpc) (Torres 2004) Detection of LMC with Fermi fg= 26.3(4.7)10-8 ph(>100 MeV) cm-2 s-1 33s D ≈ 50 kpc, i ≈ 20°-35°, diameter ≈ 8° Mgas  0.6×109 Mo (10% of Milky Way) Supernova rate 0.2 of Milky Way Dermer Saas-Fee Lecture 6 15-20 March 2010

  4. Resolving the LMC in gamma rays Total counts map Residuals (2 Gaussians) Monthly lightcurve • About 10 background blazars expected in 20° x 20° field • 6 CRATES sources associated with LAT sources outside LMC • 1 CRATES source associated within LMC boundaries • 1 flaring source near 30 Doradus during month 4 (RX J0546.8-6851?) The Fermi/LAT collaboration, Abdo et al. 2010, A&A, in press, arXiv:1001.3298 4 Dermer Saas-Fee Lecture 6 15-20 March 2010

  5. Modelling the spatial distribution Neutral hydrogen Ionized hydrogen Molecular hydrogen TS = 771.8 TS = 824.3 TS = 1110.1 • Neutral & molecular hydrogen templates poorly fit the data • Ionized hydrogen template provides best fit • Gamma-ray emission correlates little with gas (90-95% H I, 5-10% H2, 1% H II) • Exclusion of 30 Doradus region from fit does not change these findings 5 Dermer Saas-Fee Lecture 6 15-20 March 2010

  6. Cosmic-ray density LMC emissivity map Average emissivity spectrum p0 decay Bremsstrahlung Inverse Compton • Spectrum consistent with expectations from p0 decay (using local galactic p, e-, e+ spectral shapes) • Average cosmic-ray density about 0.2-0.3 times that in solar vicinity(consistent with difference between galactic and LMC SN rate) • Considerable cosmic-ray density variations • Small GeV proton diffusion length 6 Dermer Saas-Fee Lecture 6 15-20 March 2010

  7. Fermi Detects the LMC • LMC for the first time resolved in gamma rays • 30 Doradus star forming region is a bright source of gamma rays and very likely a powerful cosmic-ray accelerator • No significant point sourcecontribution (no pulsations from PSRs J0540-6919 and J0537-6910) • Gamma-ray emission correlates well with massive star forming regions and little with the gasdistribution • Compactness of emission regions suggests little CR diffusion • Average CR density ≈ 0.2-0.3 that in solar vicinity • 1.6 (0.1)×10-10 erg cm-2 s-1 7 Dermer Saas-Fee Lecture 6 15-20 March 2010

  8. GeV/TeV Emission from Starburst Galaxies • Fermi LAT has detected steady, point-like, emission above 200 MeV from three starburst galaxies • M82 (6.8σ); also detected with VERITAS (summer 2009) • NGC 253 (4.8σ); also detected with HESS (summer 2009) • NGC 4945 (reported in 1LAC; also has Seyfert nucleus) • Diffuse gamma-ray emission from cosmic-ray interactions in star-forming galaxies is most probable origin of g rays • Unresolved GeV emission, TeV emission predominantly in central region • LAT all-sky survey can point out additional candidates for TeV observatories • Observations and results • Detection significance maps • Point-like and steady • Integral fluxes consistent with galactic diffuse emission • Interpretation • Correlate star-formation with enhanced cosmic-ray intensity Dermer Saas-Fee Lecture 6 15-20 March 2010

  9. M82 Hubble Wide field and Planetary Camera 2 (NASA/ESA/R. de Grijs) NGC 253 Hubble Heritage Team (AURA/STScI/NASA) Starburst Galaxies • Starburst galaxies distinguished by regions of rapid star formation, 10-1000 × Milky Way rate • Correspondingly high supernovae rates • Dense clumps of molecular gas • Highly luminous at infrared wavelengths, radio correlation • M82 and NGC 253 • Two closest starburst galaxies (~3.5 Mpc) • Edge-on viewing angles • Small (~100 pc scale) starburst regions • Star formation rate ~10 × Milky Way rate • Lack active nuclei • Extensively studied in multiple wavebands, detailed modeling/predictions Dermer Saas-Fee Lecture 6 15-20 March 2010

  10. LAT Observations • Observation periods • 11 months (August 2008 to July 2009) • Exclude time periods when Earth limb enters field of view (rocking angle cut at 43°) • Event selection • Energy > 200 MeV • Diffuse class (cosmic-ray background contamination < 10 %) • Zenith angle < 105° • Post launch instrument response functions (P6_V3) • Model the region • 10° radius region of interest • Galactic diffuse (template / hybrid / ring) + isotropic component • Include all significantly detected LAT sources within region of interest (1st year Catalog) Dermer Saas-Fee Lecture 6 15-20 March 2010

  11. Detection Significance Maps Galactic diffuse, isotropic diffuse, and point sources subtracted Fermi LAT (>200 MeV) Fermi LAT (>200 MeV) 6o x 6o region of the sky 6o x 6o region of the sky Test Statistic (TS) = -2 log(Lsource - Lno source) 0.68, 0.95, 0.99 confidence level localization contours Appear as LAT point sources, starburst regions unresolved Dermer Saas-Fee Lecture 6 15-20 March 2010

  12. Point-like and Steady Emission • Spatial extension upper limits • Gaussian model, radius which contains 68 percent of flux (R68) • Both sources consistent with constant flux level Monthly count of the photons in the direction of each source (Aug 08 - Jul 09) Dermer Saas-Fee Lecture 6 15-20 March 2010

  13. Spectra Observed integral fluxes consistent with models of diffuse galactic gamma-ray emission, but data do not yet tightly constrain spectral shapes Dermer Saas-Fee Lecture 6 15-20 March 2010

  14. Properties of Star-Forming Galaxies SMC • Star-formation rate and gas density non-uniform throughout galaxies • uncertainty in distance measurements • Enhanced cosmic-ray intensity explains the observed starburst gamma-ray fluxes Dermer Saas-Fee Lecture 6 15-20 March 2010

  15. Gamma-ray emission from Clusters of Galaxies • Rich clusters (thousands of Galaxies; ~1015 Msun; kT ~ 5-10 keV, LX ~ 1043 - 1045 ergs s-1) • Velocity dispersions ~500-1000 km s-1 • Poor clusters(hundreds of Galaxies; ~1014 Msun; kT ~ 1-5 keV, LX ~ 1041 - 1043 ergs s-1 ) • Velocity dispersions ~250-500 km s-1 • ~5-10% of total mass of cluster; Orbital motion dominated by distribution of dark matter • Evidence for nonthermal electrons from nonthermal radio halos and relics Thermal bremsstrahlung X-ray Emission of Galaxy Clusters traces gravitational well Dermer Saas-Fee Lecture 6 15-20 March 2010

  16. Structure Formation • Density fluctuations cause region to collapse. • Magnitude of the density fluctuation determines the formation time • Larger structures form by accreting smaller clumps--hierarchical merging • Lumpy, continuous accretion Dermer Saas-Fee Lecture 6 15-20 March 2010

  17. Cluster Merger • N-body simulation of merging 1015 Mo clusters of galaxies (Berrington) Dermer Saas-Fee Lecture 6 15-20 March 2010

  18. Infall Velocity Dermer Saas-Fee Lecture 6 15-20 March 2010

  19. Shocks in Merging Clusters • Particle acceleration in clusters of galaxies • Merger shocks • Accretion shocks • Turbulent reacceleration • (0, R, ) (mass, curvature, and dark energy)=(0.3, 0.0, 0.7) • Redshift of cluster z • Cosmic Microwave Background (CMBR) dependence • UCMBR(z) = UCMBR(z=0) (1 + z)4 • Rich clusters form by accreting poor clusters Dermer Saas-Fee Lecture 6 15-20 March 2010

  20. Particle Injection • Power law distribution with exponential cutoff • Occurs only if M  1.0 • Occurs only during lifetime of shock • Normalization • Where e,p is an efficiency factor, and is set to 5%. • Typical values are Etot1063-64 ergs Dermer Saas-Fee Lecture 6 15-20 March 2010

  21. Nonthermal Photon Spectra from Merger Shocks Dermer Saas-Fee Lecture 6 15-20 March 2010

  22. Model Predictions Radio Observations of Coma vs. Model • Data points: total radio emission from Coma (Thierbach et al. 2003) • Solid curve: total radio emission from merger-shock model • Dotted curve: contributions from secondaries of nuclear production • X-ray Observations of Coma vs. ModelData from OSSE, Beppo-SAX (other data from RXTE, INTEGRAL) • Model is sum of thermal bremsstrahlung and non-thermal emission, dominated by Compton-scattered CMB radiationB = 2.2 mG Gamma-ray predictions for Coma • Detectable at high significance with GLAST and VERITAS/HESS • Predict ~10 clusters of galaxies within ~ 200 Mpc to be observed with GLAST Berrington and Dermer 2005 Dermer Saas-Fee Lecture 6 15-20 March 2010

  23. Coma A1367 M49 NGC4636 NGC5846 Hydra Centaurus A0754 Ophiuchus 3C129 Norma Perseus Triangulum AWM7 Fornax Cluster Candidates August all-sky map with prominent clusters • Observational challenges • 3C129 on galactic plane, b = 0.1° • Perseus region dominated by NGC1275 • NGC4636 region contains 3C273, about 3.5° away Dermer Saas-Fee Lecture 6 15-20 March 2010

  24. Galaxy Cluster Flux Upper Limits Compare the Fermi 7-month flux upper limits to EGRET results and predicted flux Preliminary Improved sensitivity over EGRET for each cluster Limits are comparable to model predictions of brightest clusters Dermer Saas-Fee Lecture 6 15-20 March 2010

  25. Unresolved g-Ray Background BL Lacs: ~2 - 4% (at 1 GeV) FSRQs: ~ 10 - 15% Star-forming galaxies (Pavlidou & Fields 2002)Starburst galaxies(Thompson et al. 2006) Pulsar contribution near 1 GeV Galaxy cluster shocks (Keshet et al. 2003, Blasi Gabici & Brunetti 2007) Dark matter contribution/WIMP annihilation • Contribution from unresolved sources depends on LAT point source sensitivity  decreases with LAT observation time Data: Sreekumar et al. (1998) Strong, Moskalenko, & Reimer (2000) Dermer Saas-Fee Lecture 6 15-20 March 2010

  26. Model of the Galactic foreground g-ray emission model Inverse Compton scattering g-ray emission model HI (7.5kpc < r < 9.5kpc) • Diffuse gamma-ray emission of Galaxy modeled using GALPROP • Spectra of dominant high-latitude components fit to LAT data: • Inverse Compton emission (isotropic ISRF approximation) • Bremsstrahlung and p0-decay from CR interactions with local (7.5 kpc < r < 9.5 kpc) atomic hydrogen (HI) • HI column density estimated from 21-cm observations and E(B-V) magnitudes of reddening • 4 kpc electron halo size for Compton component (2 kpc – 10 kpc tested) Dermer Saas-Fee Lecture 6 15-20 March 2010

  27. Comparison with EGRET results The Fermi-LAT collaboration 2010, PRL, in press, arXiv:1002.3603 • Considerably steeper than the EGRET spectrum by Sreekumar et al. • No spectral features around a few GeV seen in re-analysis by Strong et al. 2004 • The EGB found by the LAT is compatible with a simple power law of index 2.41+/-0.05 between 200 MeV and 100 GeV. • It is softer than the EGRET spectrum and does not show distinctive peaks (compared at EGRET sensitivity level). • ~ 15% of the EGRET EGB is resolved into sources by the LAT. • From Blazar population study: ~20%-30% of LAT EGB is due to unresolved Blazars Dermer Saas-Fee Lecture 6 15-20 March 2010

  28. Diffuse Extragalactic g-Ray Background Light from Star-Forming Galaxies Energy intensity in g rays is source g-ray luminosity g-ray luminosity of Milky Way, considered representative of star-forming galaxies  total gas mass Cosmic ray density  star formation rate/galaxy Dermer Saas-Fee Lecture 6 15-20 March 2010

  29. Diffuse Extragalactic g-Ray Background Light from Star-Forming Galaxies Space density of L* galaxies like the Milky Way “nFn” Intensity: • accounts for the greater star formation rate at z1 than now Hopkins & Beacom (2006) RH4000 Mpc (Hubble radius) Dermer Saas-Fee Lecture 6 15-20 March 2010

  30. Diffuse Extragalactic g-Ray Background Light from Star-Forming Galaxies Why bbol0.4? If number index = -2.5 GeV Dermer Saas-Fee Lecture 6 15-20 March 2010

  31. Star-forming galaxy estimate Star-forming galaxy estimate Contribution of Star-Forming Galaxies to Diffuse Extragalactic g-Ray Background The Fermi-LAT collaboration 2010, PRL, in press, arXiv:1002.3603 • Star-forming and starburst galaxies (star-formation rate higher; space density lower) make significant contribution Dermer Saas-Fee Lecture 6 15-20 March 2010

  32. Summary • Fermi maps the Large Magellanic Cloud and Small Magellanic Cloud; first maps of external normal galaxies • Fermi discovered GeV emission from starbursts M82, NGC 253 (and NGC 4945); consistent with an origin from cosmic rays • No reported detection of clusters of galaxies with Fermi • New measurement of the diffuse/unresolved extragalactic g-ray background; index -2.4 rather than -2.1 measured with EGRET • Starbursts should make a significant contribution to the diffuse extragalactic g-ray background measured with Fermi

  33. Backup Slides Dermer Saas-Fee Lecture 6 15-20 March 2010

  34. Density and Luminosity Evolution of IR galaxies:30 – 300m (900 GHz) SFR Sanders (2004) Dermer Saas-Fee Lecture 6 15-20 March 2010

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