Galactic diffuse gamma-rays

Transcription

1 Galactic diffuse gamma-rays Masaki Mori Department of Physics, College of Science & Engineering, Ritsumeikan University 1 July 31, 2009, Dept. Astronomy, Kyoto University

2 GeV gamma-ray sky by EGRET Compton Gamma-ray Observatory ( ) 2 Diffuse emission: ~80% of total gamma-ray flux!

3 Gamma-ray detection 3 Evans 1955

4 Gamma-ray detector EGRET (Energetic Gamma Ray Experiment Telescope 4

5 SAS-2 & COS-B Profile SAS-2 (Thompson et al. 1976) COS-B (Mayer-Hasselwander et al. 1982) l <5 5

6 SAS-2 & COS-B Spectrum Stecker

7 EGRET Intensity Map Galactic center Vela pulsar Geminga Cygnus region Crab 7

8 Point sources = Observed intensity Diffuse model EGRET observed intensity Diffuse model 8 Intensity model Depends on diffuse model!

9 Mattox et al., ApJ 461, 396 (1996) Likelihood analysis Maximize L to get best fit: Model = K 1 (diffuse model) +K 2 (isotropic) + i F i (PSF) i 9 Adjust K 1 &K 2 and seek for best fit with F i

10 Diffuse Emission Model Three main components: Bremsstrahlung: electron + matter + X Inverse Compton: electron + photons + X Nuclear interaction: proton(nuclei) + matter 0 2 Matter = HI + HII + H 2 Photon = 2.7K BB + FIR + NIR + Optical + UV 10

11 Two approaches GALDIF (Hunter et al.) GALPROP (Strong et al.) 11

12 Galactic Matter Distribution (GALDIF) HI : 21cm surveys Weaver & Williams (1973) Maryland-Parkes (1986) Leiden-Green Bank (1985) H 2 : N(H 2 ) = X W CO CO: Columbia CO survey at 2.6mm (1987) HII : Taylor & Cordes (1993) (pulsar dispersion / interstellar scattering measure) Interstellar radiation field : 2.7K BB + FIR + NIR + Optical + UV Local Electron spectrum : Skibo (1993) [E injection] Local Proton spectrum : Stecker (1970) [E -2.7 ] Cosmic-ray enhancement factor ρ N(HI)+N(H 2 )+N(HII) Gaussian along the Galactic axis (scaling parameter r 0 ) Only two parameters in this model : X = ( )x10 20 H-mol cm -2 (K km s -1 ) -1 r 0 = ( ) kpc Bertsch et al. ApJ 416, 587 (1993) 12

13 Hunter et al. ApJ 481, 205 (1997) Cosmic-ray Enhancement Factor (GALDIF) 13

14 Hunter et al. ApJ 481, 205 (1997) GALDIF: Longitudinal Profile MeV 14

15 Hunter et al. ApJ 481, 205 (1997) GALDIF: Latitude Profile MeV 15

16 EGRET spectrum Hunter et al. ApJ 481, 205 (1997) 16

17 GALDIF: Contribution of each components Total HI Hunter et al. ApJ 481, 205 (1997) H 2 HII IC 17

18 Observation by EGRET Hunter et al. ApJ 481, 205 (1997) b 10, 38 point sources (>5 ) removed 30MeV - 50GeV with excellent statistics (cf. COS B) General agreement with model predictions in spatial profile 40-60% excess against model predictions above 1 GeV 18 Possible solutions: Instrumental calibration error? Unresolved sources? Nuclear interaction model? Cosmic-ray spectrum?

19 19 Interstellar radiation field (GALPROP)

20 20 Gas distribution (GALPROP)

21 Strong, Moskalenko & Reimer, ApJ 613, 962 (2004) GALPROP:injection spectrum 21

22 Strong, Moskalenko & Reimer, ApJ 613, 962 (2004) GALPROP: Longitude profile 22

23 Strong, Moskalenko & Reimer, ApJ 613, 962 (2004) GALPROP: Latitude profile 23

24 Strong, Moskalenko & Reimer, ApJ 613, 962 (2004) EGRET spectrum & optimized GALPROP 24

25 Flatter Proton Spectrum? -1 Mori 1997 Standard: E -2.7 E -2.45? 25

26 Flatter Proton Spectrum? -2 Völk 2000 Souce: E -2 Transport effect 26

27 Flatter Inverse Compton? -1 Porter & Prothroe 1997 E -2.2 E -2.2 E

28 Flatter Inverse Compton? -2 Pohl & Esposito 1998 Distributed E

29 Energy calibration? Stecker, Hunter & Kniffen, Astropart. Phys. 29, 25 (2008) (a) Plot of integral (E > 1 GeV), all-sky diffuse model flux vs. EGRET observed flux for 335 < l < 45, b < 90. (b) A similar plot with a renormalization factor of (1.6) -1 applied to the observed flux. GeV anomaly exists uniformly over the whole sky and extends from high to low intensity galactic flux emission. Most likely traceable to the detector itself! 29

30 Higher energy? Amenomori et al Outer Galaxy Inner Galaxy 30

31 Ground-based observations CASA-MIA (Borione et al. 1998) 50 < l <200, -5 < b <5 ; 310 TeV mu-poor showers I /I CR < Tibet (Amenomori et al. 1997) -5 < b <5, 10 TeV, excess counts 140 < l <225 : < cm -2 s -1 sr < l < 55 : < cm -2 s -1 sr -1 EAS-TOP (Aglietta et al. 1996); 1 PeV mu-poor showers I /I CR < HEGRA (Karle et al. 1995); 80 TeV N e /Ch cut I /I CR < MILAGRO (Abdo et al. 2008); 15 TeV 8.6 excess in Cygnus region: TeV -1 cm -2 s -1 sr -1 31

32 LeBohec et al Whipple observation 4.8 FOV camera, Center: (l,b)=(40,0) 1998: 7 on/off pairs (28min. Each), >700GeV 1999: 10 on/off pairs, >500GeV Sensitivity correction across the field 32

33 Whipple results 1998: 1.84±0.57/min (3.2!) 1999: 0.42±0.43/min 33

34 HEGRA observations Pühlhofer et al telescope setup, total 105hr (1997/98) No source candidate above ¼ Crab Artificial Neural Network analysis for gamma/hadron separation in progress Lampeitl et al

35 Aharonian et al., Nature 439, 695 (2006) H.E.S.S. 35 E

36 CANGAROO-III results Ohishi et al., Astropart.Phys. 30, 47 (2008) 36

37 Limits from Balloon Experiments Hunter

38 Abdo et al., ApJ 688, 1078 (2008) Milagro Cygnus region 38

39 Milagro: latitude profile Abdo et al., ApJ 688, 1078 (2008) 39

40 Milagro: energy spectrum Abdo et al., ApJ 688, 1078 (2008) 40

41 Cherenkov2005 poster Jean-Marc Casandjian and Isabelle Grenier Dark gas contribution! 3EG catalog Extended catalog 41

42 Unveiling Extensive Clouds of Dark Gas in the Solar Neighborhood 42 Isabelle A. Grenier, Jean-Marc Casandjian, Régis Terrier, Science 307, 1292 (2005)

43 Casandjian & Grenier, I. A.AA 489, 849 (2008) Skymap of 3EG and revised catalog 3EG Hartman et al. ApJS 1999 EGR This work 43

44 Superimposed Black: 3EG Red: EGR 44

45 Isabelle A. Grenier, Jean-Marc Casandjian, Régis Terrier, Science 307, 1292 (2005) Two approaches for cosmic-ray density gradient Ring model Gas column-densities in 6 rings (boundary 3.5/7.5/9.5/11.5/13.5kpc) + IC intensity map (from GALPROP) + isotropic GALPROP model Strong et al Optimized CR spectrum to fit the GeV excess Dark gas : associated with cold and anomalous dust at the transition Between the atomic and molecular phases (Grenier et al. 2005) 45

46 Isabelle A. Grenier, Jean-Marc Casandjian, Régis Terrier, Science 307, 1292 (2005) Longitudinal profile Data 3EG Ring 46

47 Isabelle A. Grenier, Jean-Marc Casandjian, Régis Terrier, Science 307, 1292 (2005) Map of the residuals 47

48 Isabelle A. Grenier, Jean-Marc Casandjian, Régis Terrier, Science 307, 1292 (2005) Source detection 3 maps: >100MeV, 0.3-1GeV, >1GeV bin both in Galactic and equatorial coordinates Iterative detection from high T S to low T S, adding detected sources to the background model until no excess ( T S >3) was left 48

49 P. Michelson, March 2009 Fermi Gamma-ray Space Telescope Launched in June

50 50 Fermi/LAT: first 3 months

51 51 0FGL: ApJS 183, 46 (2009)

52 52

53 53

54 3EG / EGR / 0FGL: close up 54 No good consistency around the Galactic center

55 55 LAT: Galactic diffuse emission

56 56 LAT: Galactic mid-latitude diffuse

57 Aharonian et al. Nature 439, 695 (2006) HESS image of the Galactic center region 57 Active accelerators in the last 10 4 years? Sgr A East (SNR) or Sgr A*?

58 Calculation of diffuse gamma-rays Input parameters: Proton/electron injection spectrum Local interstellar spectrum Galactic spectrum? Cosmic-ray composition in the Galaxy Interaction cross section for protons/nucleus Matter and radiation distribution in the Galaxy (3D) Gas distribution Atomic abundance H:He:CNO:NeMgSiS:Fe=1 : : : : following the compilation by Meyer (1985) Honda et al

59 pp 0 cross section 59 Moskalenko et al., GLAST symposium, Feb. 2007

60 Nuclear enhancement factor 60 Mori, Astropart. Phys. 31, 341 (2009)

61 Nuclear enhancement factor 61 Mori, Astropart. Phys. 31, 341 (2009)

62 62 Energy dependence

63 Fermi ScienceTools (2009Feb) Fermi diffuse model Wait for details! Fermi EGRET 63

64 Added 01-SEP-2009 Fermi diffuse model gll_iem_v02.fit (2009Aug) Latest! Fermi EGRET 64

65 Summary Galactic diffuse gamma-rays are the most abundant class of gamma-rays in the GeV sky, and are the background for point source detection. Diffuse gamma-rays above 1 GeV observed by EGRET showed a flatter spectrum than expected. Fermi observations (mid-lat. range) can be accounted assuming normal cosmic ray spectrum. (But be patient for their results on the plane!) Observation of the Galactic Plane in the TeV region is difficult, but there are some indications near the Galactic center and along the plane. 65

66 Abdo et al. 2009ApJ 696,1084 Vela pulsar by Fermi 66 Spectral mismatch between EGRET and Fermi!