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GeV ガンマ線観測による星間ガス・宇宙線研究の現状

GeV ガンマ線観測による星間ガス・宇宙線研究の現状. 2014 年 9 月 11 日 @ 山形大学 ( 日本天文学会秋季年会 ) 水野　恒史 ( 広島大学宇宙科学センター ) Fermi-LAT Collaboration. Cosmic Gama Radiation as a Tracer of the Interstellar Medium and Galactic Cosmic-Rays. Sep 11, 2014@Yamagata T. Mizuno (Hiroshima Astrophysical Science Center)

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GeV ガンマ線観測による星間ガス・宇宙線研究の現状

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  1. GeVガンマ線観測による星間ガス・宇宙線研究の現状GeVガンマ線観測による星間ガス・宇宙線研究の現状 2014年9月11日@山形大学(日本天文学会秋季年会) 水野　恒史 (広島大学宇宙科学センター) Fermi-LAT Collaboration

  2. Cosmic Gama Radiation as a Tracer of the Interstellar Medium and Galactic Cosmic-Rays Sep 11, 2014@Yamagata T. Mizuno (Hiroshima Astrophysical Science Center) on behalf of the Fermi-LAT Collaboration

  3. Outline • Introduction: g-rays as a probe of interstellar medium (ISM) and Cosmic-rays (CRs) • Dark gas and XCO seen in g-rays • Galactic CRs measured by g-rays

  4. All-Sky Map in g-Rays • GeVg-ray sky = Point sources + Diffuse g-rays >=80% of g-rays Geminga Vela Galactic plane Crab 3c454.3 Fermi-LAT 4 year all-sky map

  5. All-Sky Map in Microwave • Planck microwave map (30-857 GHz) = dust thermal emission = ISM Galactic plane nearby gas in high latitude

  6. Processes to Produce g-rays (1) g-rays = CRs x ISM (or ISRF) Cosmic-rays Interstellar Medium Fermi-LAT or IACTs • known ISM distribution => CRs • those “measured” CRs => ISM A powerful probe to study ISM and CRs (g-rays directly trace gas in all phases)

  7. Fermi-LAT Performance • Large FOV (~2.4 sror ~0.2 x 4psr) • Large effective area (>=0.7 m2 in >= 1 GeV) • Moderate PSF (~0.8 deg@1 GeV, ~0.2 deg@10 GeV) http://www.slac.stanford.edu/exp/glast/groups/canda/lat_Performance.htm Effective Area(P7rep) PSF Ackermann+12, ApJS 203, 4 (CA: Baldini, Charles, Rando) Bregeon+13, arXiv:1304.5456

  8. All-Sky Map in Microwave • Planck microwave map (30-857 GHz) = dust thermal emission = ISM Cepheus & Polaris Taurus Orion R CrA Chamaeleon MBM53,54,55 nearby molecular clouds in high latitude

  9. All-Sky Map in g-Rays • GeVg-ray sky ~ Diffuse g-rays ~ Cosmic Rays (CRs) x ISM Fermi-LAT 4year all-sky map Cepheus & Polaris Taurus Orion R CrA Chamaeleon MBM53,54,55 detailed study of individual clouds (+ISM in galactic plane) published

  10. Outline • Introduction: g-rays as a probe of interstellar medium (ISM) and Cosmic-rays (CRs) • Dark gas and XCO seen in g-rays • Galactic CRs measured by g-rays

  11. Modeling of g-ray Data • Under the assumption of a uniform CR density, g-rays can be represented by a linear combination of template maps ∝ICR ∝(ICR x XCO) Fermi-LAT data qCOx WCO qHIx N(HI) + = (2.6 mm) (21 cm) Isotropic Inverse Compton + + ∝(ICR x XDG) (e.g., galprop) qDGx dustres + Dark Gas (gas not properly traced by HI and WCO) + point sources (HI is usually assumed to be opt-thin; Ts>=120K) (WCO is not a all-sky map, may miss some fraction of H2)

  12. Modeling of g-ray Data • Under the assumption of a uniform CR density, g-rays can be represented by a linear combination of template maps ∝ICR ∝(ICR x XCO) Fermi-LAT data qCOx WCO qHIx N(HI) + = (2.6 mm) (21 cm) Isotropic Inverse Compton + + ∝(ICR x XDG) (e.g., galprop) qDGx dustres + Dark Gas (gas not properly traced by HI and WCO) + point sources g-rays directly trace gas in all phases

  13. Dark Gas (Dark Neutral Medium) • Grenier+05 claimed there exist considerable amount of gas not properly traced by radio surveys (HI by 21 cm, H2 by 2.6 mm CO) surrounding nearby CO clouds • cold HI? CO-dark H2? Grenier+05, Science 307, 1292 center@l=70deg E(B-V)excess(residual gas inferred by dust) and Wco “Dark-gas” inferred by g-rays (CGRO EGRET) Confirmationand detailed study by current telescopes are important

  14. Dark Gas Seen in GeVg-rays (1) • ISM has been mapped by radio surveys (HI by 21 cm, H2 by 2.6 mm CO) • Fermi revealed a component of ISM not measurable by those standard tracers Chamaeleon Molecular Cloud Residual g-rays when fitted by N(HI)+WCO g-rays w/ CO contour Ackermann+12, ApJ 755, 22 (CA: Hayashi, TM)

  15. Dark Gas Seen in GeVg-rays (2) • ISM has been mapped by radio surveys (HI by 21 cm, H2 by 2.6 mm CO) • Fermi revealed a component of ISM not measurable by those standard tracers, confirming an earlier claim based on EGRET study (Grenier+05) Residual g-rays when fitted by N(HI)+WCO Residual gas inferred by dust Ackermann+12, ApJ 755, 22 (CA: Hayashi, TM) (“dark-gas“ no longer dark in g-rays)

  16. Amount of Dark Gas Residual g-rays when fitted by N(HI)+WCO • Fermi revealed a component of ISM not measurable by those standard tracers • Amount of “dark gas” is comparable to or greater than gas mass traced by WCO (Both MH2(CO) and MDG∝ ICR∝ N(HI)) See also Abdo+10 (ApJ 710, 133), Ackermann+11 (ApJ 726, 81) and Ackermann+12 (ApJ 756, 4)

  17. XCO and XDG by g-rays • No apparent spectral change in qCO/qHI and qDG/qHI, indicating CR penetration to dense H2 (CO) and dark gas low E High E XCO~1x1020 cm-2 (K km/s)-1 XAV~2x1022 cm-2 mag-1

  18. Compilation of Xco • g-rays are a useful probe to study Xco • Penetrate the clouds • CR density can be estimated from nearby HI regions • Does not depend on assumptions about the dynamical state Nearby clouds show smaller Xco Study of other clouds is important individual clouds (NB green shaded region was determined using an a priori assumption on CR flux)

  19. Outline • Introduction: g-rays as a probe of interstellar medium (ISM) and Cosmic-rays (CRs) • Dark gas and XCO seen in g-rays • Galactic CRs measured by g-rays

  20. Measurement of local ICR(1) • High lat. HI cloud in 3rdquadrant • small contamination of IC and molecular gas • correlate g-ray intensity with N(HI) • Linear relation between N(HI) and Ig indicates uniform CR density in ROI (Ts=125 K assumed) Abdo+09, ApJ 703, 1249 (CA: TM)

  21. Measurement of local ICR (2) • High lat. HI cloud in 3rdquadrant • small contamination of IC and molecular gas • correlate g-ray intensity with N(HI) LAT data model from the LIS • Local CR spectra ~ those directly measured at the Earth(uCR~1 eV/cm3) nucleon-nucleon electron-bremsstrahlung Abdo+09, ApJ 703, 1249 (CA: TM)

  22. All-Sky Average local ICR Data Model • on average, local CR spectra ~ those measured at the Earth(uCR~1 eV/cm3) Casandjian 12 Casandjian+ in prep.

  23. Compilation of local ICR • “local” CR densities among regions agree by a factor of 1.5, within systematic uncertainty (mostly due to the assumption of Ts) All-sky average individual cloud

  24. Uncertainty due to HI Optical Depth • g-ray emissivity, or ICR, depends on HI optical depth assumption • uncertainty by a factor of ~1.5. also affects MH2, MDG • cross correlation among g-rays, radio, IR and optical is crucial Sun Local Arm Outer arm interarm Perseus Arm Local arm interarm Perseus arm NASA/JPL-Caltech/R. Hurt Ackermann+11, ApJ 726, 81 (CA: Grenier, Mizuno, Tibaldo)

  25. Summary • g-rays are a powerful probe to CRs and ISM • (ISM) optically thin, directly traces all gas phases • (CR) emissivity spectra can be inverted to CR spectra • Dark gas has been revealed through MW investigation including g-rays • important component of the ISM: MDG≧ MH2(CO) • Uncertainty of HI optical depth has considerable impact of the measurement of ICR, MDG, MH2(CO), etc. • cross correlation among MW data is crucial Thank you for your Attention

  26. Reference • Dame et al. 2001, ApJ 547, 792 • Kalberla et al. 2005, A&A 440, 775 • Grenieret al. 2005, Science 307, 1292 • Atwood et al. 2009, ApJ 687, 1071 • Abdo et al. 2009, ApJ 703, 1249 • Abdo et al. 2009, PRL 103, 251101 • Abdo et al. 2010, ApJ 710, 133 • Ackermann et al. 2011, ApJ 726, 81 • Fukui et al. 2012, ApJ 746, 82 • Ackermann et al. 2012, ApJS 203, 4 • Ackermann et al. 2012, ApJ 750, 3 • Ackermann et al. 2012, ApJ 755, 22 • Ackermann et al. 2012, ApJ 756, 4 • Casandjian 2012, AIP Conf Proc. 1505, 37 • Bregeon et al. 2013, arXiv:1304.5456 • Planck 2013 results XI, arXiv:1312.1300 • Fukui et al. 2014, arXiv:1401.7398

  27. Backup Slides

  28. Fermi Gamma-ray Space Telescope • Fermi = LAT + GBM • LAT = GeV Gamma-ray Space Telescope (20 MeV ~ >300 GeV; All-Sky Survey ) (GC-emphasized observation started in 2013 Dec.) 2008.06launch 2008.08 Sci. Operation 3c454.3 Cape Canaveral, Florida 1873 sources Nolan+ 2012, ApJS 199, 31

  29. g-ray Telescopes Imaging Atmospheric Cherenkov Telescopes (HESS, MAGIC, VERITAS) 30 GeV-10 TeV, FOV of a few degree Fermi-LAT (Satellite) 20 MeV-300 GeV, FOV of ~2.4psr GeVg-rays (<100 GeV) by Fermi-LAT TeVg-rays (>100 GeV) by IACTs

  30. Processes to Produce g-rays (2) g-rays = CRs x ISM (or ISRF) g-ray data and model (mid-lat. region) p0 decay, G~2.7 (isotropic) Bremsstrahlung, G~3.2 Abdo+09, PRL 103, 251101 (CA: Porter, Strong, Johanneson) Inverse Compton, G~2.1 A powerful probe to study CRs and ISM Pro: optically-thin, “direct” tracer of all gas phases Con: low-statistics, contamination (isotropic, IC), depend on CR density

  31. Dark Gas Seen in TeVg-rays • Fukui+12 claimed there exist considerable amount of “dark HI” in RX J1713.7-3946 by comparing HI, CO and g-rays Np(H2) Corrected Np(HI) Np(Htot) TeVg-ray (H.E.S.S.)

  32. Origin and Propagation of Galactic CRs • uCR~1 eV/cm3 at the solar system • Vgal=1067-68 cm3, tesc~107 yr • ESN~1051 erg, FSN~1/30 yr • If h~0.1 PCR~1041 erg/s Pinj~1041 erg/s • To test this SNR paradigm of CRs, • we need to observe • CRs accelerated at SNRs and star-forming regions • CR distribution in MilkyWay (MW) sun

  33. GeVg-ray as a tracer of CRs and ISM • For local CR, the g-ray emissivity is • Then, the g-ray luminosity is Qg(>100MeV) ~ 1.6x10-26ph/s/sr/H-atom ~ 1.5x10-28 erg/s/H-atom Lg(>100MeV)~(Mgas/mp)*Qg ~1039 erg/s g-ray (compatible to Galactic Ridge X-ray Emission) MW is bright in g-rays! probe to study CR origin & propagation, ISM distribution sun

  34. (Old) Fermi-LAT Performance • New Dataset and Response (Pass7, 2011.08-) • Improved Aeff in low Energy (E<200 MeV) • In-orbit calibration of PSF http://www.slac.stanford.edu/exp/glast/groups/canda/lat_Performance.htm Old Aeff(P6) Big improvement over the old P6 response in E<200 MeV If you want to analyze data by yourself, please visit Fermi Science Support Center http://fermi.gsfc.nasa.gov/ssc/

  35. (New) Fermi-LAT Performance • New Dataset and Response (P7REP, 2013.09-) • calibration constants improved with respect to P7V6 (CAL position reconstruction affects PSF) http://www.slac.stanford.edu/exp/glast/groups/canda/lat_Performance.htm Effective Area(P7rep) PSF Ackermann+12, ApJS 203, 4 (CA: Baldini, Charles, Rando) Bregeon+13, arXiv:1304.5456 good enough for multiwavelengthanalysis of X-ray / TeVg-ray sources

  36. Pass8 • Pass 8 is a comprehensive revision of the Fermi-LAT analysis chain Preliminary background rejection => ~25% increase in HE acceptance ~100% increase in LE acceptance

  37. CRs on Galactic Scale No single model to reproduce the all-sky data best, but overall agreement is good Outer Galaxy Diffuse model (total) Local pi0 e- brems. IC Inner Galaxy Ackermann+12, ApJ 750, 3 (CA: Johannesson, Porter, Strong) 1GeV 10 100

  38. The Outer Galaxy (Top view) Galactic Center Sun II quad III quad NASA/JPL-Caltech/R. Hurt

  39. The Outer Galaxy (Top view) • No distance ambiguity in velocity separation of gas • suitable to study CRs associated with arms and interarm regions Sun Local Arm Outer arm Perseus Arm II quad III quad NASA/JPL-Caltech/R. Hurt

  40. Data Analysis g-rays • “Standard” approach: • linear combination of ISM maps • - no a-priori assumption of CR spectra = N(HI),2 N(HI),1 N(HI),3 N(HI),4 +qHI,2X qHI,1X +qHI,3X +qHI,4X interarm Perseus arm Outer arm Local arm WCO,1 WCO,2 WCO,3 +qCO,1X +qCO,2X +qCO,3X E(B-V)res +qEBVX +IC+Iso+PS

  41. ISM Component not visible by Standard Tracers • Fermi revealed ISM gas not traced by radio surveys Residual when fitted by N(HI)+WCO excess gammas = residual gas Ackermann+11, ApJ 726, 81 (CA: Grenier, Mizuno, Tibaldo)

  42. ISM Component not visible by Standard Tracers • Fermi revealed ISM gas not traced by radio surveys • confirming an earlier claim based on EGRET study (Grenier+05) Residual when fitted by N(HI)+WCO Residual gas inferred by dust Ackermann+11, ApJ 726, 81 (CA: Grenier, Mizuno, Tibaldo)

  43. Uncertainty due to HI Optical Depth • g-ray emissivity, or ICR, depends on HI optical depth • uncertainty by a factor of ~1.5 • cross correlation among g-rays, radio, IR and optical is crucial Local arm interarm Perseus arm Ackermann+11, ApJ 726, 81 (CA: Grenier, Mizuno, Tibaldo)

  44. Uncertainty of Physics Process Model • Uncertainty of the Physics Model affects the g-ray emissivity, or ICR, at 10-20% level Dermer12, PRL 109, 091101

  45. dust-WHI relation • Large scatter of dust-WHI relation has been recognized recently. Whether this is due to (1) optically-thick HI, or (2) non-uniform dust property, is under debate. (e.g., Fukui+14ab, Planck Collaboration 2013) • Correlation with g-ray is important to settle the issue Fukui+14a

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