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Synchrotron and other Low-Frequency Science

Synchrotron and other Low-Frequency Science. J. P. Leahy. Picture: GALFACTS Collaboration. Overview. Synchrotron Physics (Galactic) Component separation for foregrounds What can COrE tell us that we don’t know already from WMAP and Planck ? Current ground-based work

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Synchrotron and other Low-Frequency Science

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  1. Synchrotron and other Low-Frequency Science J. P. Leahy Picture: GALFACTS Collaboration Beyond COrE Workshop, Paris

  2. Overview • Synchrotron Physics (Galactic) • Component separation for foregrounds • What can COrEtell us that we don’t know already from WMAP and Planck? • Current ground-based work • What about extragalactic low-frequency sources (AGN)? Beyond COrE Workshop, Paris

  3. Synchrotron Physics • Cosmic ray leptons (electrons, mostly) • Origin • Propagation • Distribution • Magnetic Fields (at source) • Structure • Coherent/Ordered/Random • Intensity • Propagation effects • Faraday Rotation • Free-free absorption Beyond COrE Workshop, Paris

  4. Origin of CR • Supernova remnants prominent in Galactic synchrotron emission • Strong shocks • Pulsar winds Beyond COrE Workshop, Paris

  5. Shock acceleration • First-order Fermi (e.g. Bell 1978): • N(E) E−s, I  −, s = 2+1 • s = (r+2)/(r− 1) • r = 4 for strong adiabatic shock: s = 2,  = 0.5 • r < 4 weak shock: s > 2,  > 0.5 • r = 7 relativistic shock • s = 4/3,  = 0.167 (Test particle) • Complicated (CR-dominated) • r >> 4 cooling shock • but fast particles don’t see this compression ratio Beyond COrE Workshop, Paris

  6. SN 1006 VLA (Dyer et al 2009) Chandra (NASA/CXC) Beyond COrE Workshop, Paris

  7. SN 1006 • Shock front Radio-X-ray: •  = 0.50  0.02 • Decourchelle et al (2011) • X-ray synchrotron  = 1.5 • Cutoff in spectrum just below X-ray band • Highest-energy electrons ~ 100 TeV • Thin shock suggests r > 4 • Barrel shape: • Efficient acceleration at parallel shocks? • Contrary to Bell model! • SN1006 has radial B-field Beyond COrE Workshop, Paris

  8. Complexities • Significant variation in SNR spectral indices • Pulsar Wind nebulae flatter, e.g. Crab  = 0.3 • Balance between steepening spectrum of old material and injection of new material: • Young SNR (+radio SN) have steeper spectra. Beyond COrE Workshop, Paris

  9. Spectral Index: 13:7 mm • Low sensitivity in WMAP data at λ < 1.3 cm gives limited sky coverage • Note flat spectrum for Crab nebula • Mean βP≈ −3.0 • Slightly flatter than at lower frequencies. (−3.1 in same regions) • Kogut et al (2007) claim detection of flattening from βP≈ −3.2 to −3.0 from WMAP data alone… • Use smoothing from 7° to 18° • No allowance for pol. bias at 23GHz: artifact? (3-year WMAP data) Beyond COrE Workshop, Paris

  10. Spatial distribution of Synchrotron • External galaxies show SR most intense in spiral arms • (M51 extreme case) • Highest fractional polarization in interarms • Field more ordered Beyond COrE Workshop, Paris

  11. 3D Emission models • Milky Way also has distinct radio spiral arms • Consistent with arms in NE2001 model. • Cosmic ray analysis suggests CRs very smoothly distributed • e.g. Fermi: outer galaxy ≈ constant density • Major variation in B-field • Hammurabi code • Waelkens, Jaffe et al. • Sun et al (2008) • Jaffe et al (2010) • Fit: • 408 MHz I • 23 GHz p NE2001 electron density contours Beyond COrE Workshop, Paris

  12. Propagation effects • Ambient spectrum of CRs in ISM is steady state between injection & loss • radiative, diffusive, convective • Direct measurement in good agreement with inferred spectrum from synchrotron emission (B ~ 6 G) • Detailed modelling suggests injection spectrum with several breaks, very hard at low frequency (s~1.6) • C.f. Orlando, Strong & Jaffe (2011) • Jaffe et al 2011: E3 scaling • GALPROP prediction fitted to synchrotron data vs local e− spectrum. Beyond COrE Workshop, Paris

  13. Galactic Halo: not a plane slab! • 408 MHz I + 23 GHz P • Minimum intensity at mid latitudes • Synchrotron monopole: • Cosec|b|fit to Haslam map: zero level = 9.8 K (N), 10.1 K (S) • But already zeroed to 3 K • Would give negative intensity at faintest points • cf ARCADE2 • Isotropic component! • Local bubble or halo? Beyond COrE Workshop, Paris

  14. The Synchrotron Sky • On large scale mostly dominated by coherent structures • Loops (local) • Fan (c. 1 kpc) • SNRs • Not a lot of scope for meaningful statistical analysis • higher resolution needed! Beyond COrE Workshop, Paris

  15. Loops • Only Loop I and top half of Loop III clear ? ? ? ? Beyond COrE Workshop, Paris

  16. NGP Polarization • Polarization well organized across NGP • Fractional polarization low outside Spur: ~ 10% • Complex structure along LOS • Field in Spur follows outside field • Bright rim effect? Beyond COrE Workshop, Paris

  17. Component separation • Needed to do foreground science as well as for CMB! • Since Planck designed, Anomalous Microwave Emission discovered • Significant contributor 10-60 GHz • Quite variable spectrum, peak 20-40GHz Beyond COrE Workshop, Paris

  18. rms Q,U @ 1° E B, r=0.1 3.4% anomalous dust 10% thermal dust artefacts at 100 & 217 GHz from CO lines Polarized Foregrounds QUIJOTE Beyond COrE Workshop, Paris

  19. WMAP/Fermi/Planck “Haze” • Planck, after subtraction of templates for all major components • NB: template fit pretty good! • ESA press release Feb 2012 • Fermi , E > 10 GeV • NASA press release Jan 2012 Beyond COrE Workshop, Paris

  20. Interpreting the haze • Existence of “haze” conclusively demonstrated • Interpretation: • Two components,  = 0.5 and  = 1 • Implicit in template method • Region with single unusual  = 0.7 • Very hard to distinguish without ultra-precise measurements • Illustration assumes 2% errors for WMAP/Planck, except at > 50 GHz • Actual errors dominated by residuals from other foregrounds Beyond COrE Workshop, Paris

  21. Continuous continuum • Synchrotron spectra are very smooth • Monoenergetic kernel • Nearly power-law electron distribution • Similarly • free-free • Spinning dust • Thermal dust • Synchrotron spectrum of mono-energetic electrons • Black body Beyond COrE Workshop, Paris

  22. Continuous Continuum • Power law is just an approximation… • …but a good one • The best-measured synchrotron sources are well fit by a 2nd-order log-log polynomial over 2 decades of frequency Beyond COrE Workshop, Paris

  23. Power-law electron distribution? Assumes 6 G • Fermi shows electron spectrum really is smooth • NB: Emission frequency E • Stay tuned for AMS2 results • Departures from power law expected at high E where propagtion time from nearest source ~ radiative lifetime • ~50 TeV? • Optical band! Jaffe et al (2011) Beyond COrE Workshop, Paris

  24. COrE contribution • More frequencies: • Maybe we will have more frequency points than parameters to fit! • Better-defined frequencies because bands are narrower • Including significantly smaller colour correction • Hopefully more resources devoted to getting accurate bands in pre-launch calibration • High sensitivity: component discrimination depends on differences between adjacent bands • Easy to run out of SNR • Especially if bands are close together • BUT fundamentally, with all components smooth, subdividing bands rapidly stops giving new information • Very likely CMB+AME+Synch + Free-Free + dust is fundamentally ambiguous • NB: monopole uncertainty doesn’t help. Beyond COrE Workshop, Paris

  25. Meanwhile, back on the ground… • Many surveys exist but quality uneven • Strong et al (2011) for an up-to-date list • Complications: • Below 300 MHz: free-free absorption, especially in the plane • Above 1 GHz: free-free emission • Below 5 GHz Faraday rotation • Above 10 GHz: AME Guzmán et al 2011 Beyond COrE Workshop, Paris

  26. GMIMS/STAPS: IQU at 21 cm • Replacement for DRAO/Villa Elisa 21 cm survey • Fully sampled, 30′ beam • 1.3 -1.8 GHz • 2048 channels • for RM Synthesis • I as well as Q U • South from Parkes • STAPS (PI Haverkorn) • Also ‘low’ band: 300 -900 MHz. Wolleben et al (2010, ApJL) Beyond COrE Workshop, Paris

  27. GALFACTS GALFACTS fields overlaid on Stockert Survey • Continuum Transit Survey with Arecibo L-Band Feed Array • 32% of sky • 3 arcmin beam • 300 MHz • 2048 channels • Final maps will use GMIMS to recover large-scale structure Beyond COrE Workshop, Paris

  28. S-PASS • 2.3 GHz Southern-sky polarization survey with Parkes • 9′ beam • Data collected, processing under way • Much less depolarized than 21 cm. • Figs from Carretti (2011) • ATNF Newsletter Beyond COrE Workshop, Paris

  29. C-BASS • 5 GHz all-sky survey • IQU, 48′ beam • Planck-like pseudo-correlation total power receiver combined with correlation polarimeter. • Telescope optimised to minimise sidelobes • Owens Valley (north) • Karoo (south) Beyond COrE Workshop, Paris

  30. QUI JOintTEnerife experiment 11-30 GHz Telescope recently installed on Teide Aim to map ~ ¼ of sky at 15 GHz in full polarization QUIJOTE Beyond COrE Workshop, Paris

  31. Point sources before WMAP • Prior to WMAP, there were no large-area surveys from 6 cm to 100 m • Previously, pioneering this much new territory has yield unexpected phenomena • quasars, pulsars, X-ray binaries, Gamma-ray bursts, ULIRGs… • But WMAP and Planck LFI ERCSC show only expected blazar-type AGN • HFI point sources are also the expected SMGs • Deeper surveys @ < 70 GHz with COrE-sized telescope will rapidly hit the confusion limit • LFI close to confusion at 30 GHz • Ground-based surveys already far deeper • and SKA is coming… Beyond COrE Workshop, Paris

  32. Extragalactic source (AGN) • Old questions: • What is the central engine? • How does it make relativistic jets? • How do jets propagate to Mpc scales? • How does the AGN population evolve cosmologically? • New questions • What do AGN do to their environment? • Regulate cluster cooling? • Provide entropy floor? • Use as Faraday probes to study growth of cosmic magnetic fields Beyond COrE Workshop, Paris

  33. Point sources Beyond COrE Workshop, Paris

  34. Faraday rotation in radio galaxies Guidetta et al (2011) Beyond COrE Workshop, Paris

  35. Faraday rotation in radio galaxies Beyond COrE Workshop, Paris

  36. What we want to know about AGN • Radio/X-ray interactions to probe dynamics • VLBI movies to probe dynamics • Variability • Large samples for statistics/rare cases • Polarization structure and wavelength-dependence to probe local and line-of-sight Faraday rotation • Must be spatially resolved! Beyond COrE Workshop, Paris

  37. The Competition GBT LMT ALMA ASKAP JVLA Meerkat/ SKA Beyond COrE Workshop, Paris

  38. The Competition (cont) Beyond COrE Workshop, Paris

  39. Summary • COrE features: • many bands, high sensitivity, narrow(er) bands will all help untangle low frequency foregrounds • If frequency coverage extends  100 GHz • …and we avoid spectral lines! • BUT problem is fundamentally insoluable: not clear whether approximate solutions can be good enough to give interasting astrophysics. • COrE band is not of critical interest for synchrotron radiation • COrE measurements of AGN are not competitive with ground-based instruments. Beyond COrE Workshop, Paris

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