Cosmic rays in the local interstellar medium

Transcription

1 Cosmic rays in the local interstellar medium Igor V. Moskalenko Igor V. Moskalenko/NASA-GSFC 1 LMC (Magellanic Cloud Emission Nuclear Data-2004/09/28, Line Survey: Smith, Points) Santa Fe R - H G - [S II] B - [O III]

2 MCELS: Smith, Points Supergiant shells ~ 1000 pc ~ 107 yr (multi generations) Superbubbles ~ 100 pc ~ 106 yr (OB associations) Bubbles, SNRs ~ pc ~ yr (single star) 500 pc Igor V. Moskalenko 2 R - H G - [S II] B - [O III]

3 LMC Superbubble: N70 LMC Superbubble: N57 Red: H Green: [O III] Blue: X-ray Igor V. Moskalenko 3 LMC Superbubble: N11

4 Motivation SNRs are the conventional sources of the majority of CRs Multiple SN explosions within a single OB association may have a profound effect on CR spectra and CR distribution in a galaxy May leave signatures in isotopic source abundances (e.g. 22Ne) The evolution of a SNR shell in a superbubble (rarefied ionized gas) may be quite different from that of a SNR in the typical cold ISM (e.g. may accelerate to higher energies) Igor V. Moskalenko 4

5 Why is the local interstellar medium? Can be probed fairly well assuming the spectra of CR species do not change much within ~100 pc (see yesterday s talk by Seth Digel) May have measurable signatures due to the proximity of the sources and propagation effects (e.g. PAMELA positron fraction, breaks in p & He spectra at 230 GV) May produce visible effects on the gamma-ray skymaps (e.g features and residuals) Igor V. Moskalenko 5

6 Fermi-LAT residual skymaps (submitted to ApJ) PRELIMINARY Model 44: LorimerZ6R20T C5 (see Gulli s talk) Igor V. Moskalenko 6

7 Local Bubble X-Y plane X-Z plane Igor V. Moskalenko 7

8 The origin of the Local Bubble The LB - low-density region around the Sun, filled with hot/warm H I gas The size of the region is about 200 pc It is likely that the LB was produced in a series of SN explosions Most probably its progenitor was OB star associations The age ~10 Myr, the last SN explosion was ~1 2 Myr ago, or three SNs during the last 5 Myr A detailed study (Abt 2011) shows three different regions with different ages: The region towards the Galactic center ~4 Myr (with a pulsar ~4 Myr old) The central lobe <160 Myr Pleiades lobe ~50 Myr Igor V. Moskalenko 8

9 450 pc in the solar neighborhood Hot ionized gas OB associations High density molecular clouds around starforming regions Credit: Frisch Igor V. Moskalenko 9

10 The location of interstellar clouds in the Galactic Plane Igor V. Moskalenko 10

11 Four closest warm clouds Shapes of the four closest to the heliosphere interstellar clouds (edges within 1-5 pc) in Galactic coordinates Linsky&Redfield 2009 Igor V. Moskalenko 11

12 The morphologies of 15 clouds (within 15 pc) Frisch Igor V. Moskalenko 12

13 Mean extinction for stars within 500 pc Magenta contours interaction of Loop I with the LB Rings OB associations Black contours the integrated stellar radiation at 1565 Å (TD-1 satellite) Igor V. Moskalenko 13 Frisch 2007

14 44: LorimerZ6R20T C5 Igor V. Moskalenko 14

15 Effects on Cosmic Rays Igor V. Moskalenko 15

16 Propagation of CRs Effect of the local underdensity on radioactive clock isotopes 10Be, 26Al, 36Cl (Donato+ 2002) Reduces the abundance of radioactive isotopes at the position of the Sun 36Cl/Cl is the most sensitive (shortest half-life) Affects propagation parameters However, the diffusion coefficient in the LB is unknown Igor V. Moskalenko 16

17 Propagation of CRs Effect on propagation parameters due to the local component of CRs at low energies (Moskalenko+ 2003). Only primary local elements were considered Increased abundances of primary elements (C, O, Fe ) at LE Secondary elements are produced by Galactic CRs and are not produced by the local CRs Affects propagation parameters: more secondaries to be produced Galaxy-wide (e.g., larger B/C) Igor V. Moskalenko 17 Galactic Local

18 Total inelastic nuclear cross sections ² ² ² Ekin, MeV/nucleon Igor V. Moskalenko 18 The inelastic cross section gives a probability of interaction Rises with the atomic number as ~A2/3 As the result of interaction the original nucleus is destroyed Wellisch & Axen 1996

19 Effective propagation distance: LE nuclei ² The interaction time scale at ~1 GeV 1 TeV: τ ~ L/c ~ [σnc]-1 ~ /[0.25 (A/12)2/3] s ~ yr (A/12) 2/3 σcarbon(a=12) 250 mb;n ~ 1 cm 3 (in the plane) ² The diffusion coefficient (4 kpc halo): D ~ R1/2 cm2/s, R rigidity in GV Effective propagation distance (in the plane): <X> ~ 6Dτ ~ R1/4 (A/12) 1/3 cm ~ 1.5 kpc R1/4 (A/12) 1/3 Helium: ~ 2.1 kpc R1/4 Carbon: ~ 1.5 kpc R1/4 0.36% of the surface area (25 kpc radius) Iron: ~ 0.9 kpc R1/4 0.16% (anti-) protons:~ 6 kpc R1/4 5.76% ² ² γ-rays: probe CR p (pbar) and e± spectra in the whole Galaxy ~50 kpc across Igor V. Moskalenko 19

20 Direct probes of CR propagation ² ² Fe C p 50 kpc Igor V. Moskalenko 20 Direct measurements probe a very small volume of the Galaxy The propagation distances are shown for rigidity ~1 GV

21 Energy losses of electrons ² ² Igor V. Moskalenko 21 The ionization and Coulomb losses are calculated for the gas number density 0.01 cm-3 Energy density of the radiation and magnetic fields 1 ev cm-3 (Thomson regime)

22 Effective propagation distance: HE electrons ² The energy loss time scale (IC) at ~1 GeV 1 TeV: τ~ 300 E12 1 kyr ~ 1013 E12 1 s; E12 energy in TeV ² ² ² The diffusion coefficient: D ~ (0.5-1) 1030 E121/2 cm2/s Effective propagation distance: <X> ~ 6Dτ ~ E12 1/4 cm ~ 1 kpc E12 1/4 ~ a few kpc at 10 GeV The cutoff energy of the electron spectrum ~1 TeV can be used to estimate the distance to the local HE electron sources: a few 100 pc. Igor V. Moskalenko 22

23 Direct probes of CR propagation ² ² Fe, TeV e C p, 10 GeV e 50 kpc Igor V. Moskalenko 23 Direct measurements probe a very small volume of the Galaxy The propagation distances are shown for nuclei for rigidity ~1 GV, and for electrons ~1 TeV

24 The origin of cosmic rays Igor V. Moskalenko 24 WR-124 in Sagittarius Hubble Image

25 Detailed comparison 20Ne 32S 40Ca 22Ne 53Mn* 41Ca* P 15N F 55Mn 33S Good ScTiV Xsections Well-known IM Igor V. Moskalenko 25

26 Igor V. Moskalenko 26

27 A-dependence of the source abundance ratio Meyer Igor V. Moskalenko 27

28 Relative isotopic source abundance Ratio Relative to Solar System Abundances 6 5 WR Model CRIS data (Binns et al. 2005) Combined data corr for volatility New CRIS UH-Isotopes Model source abundance: 80% solar + 20% Wolf-Rayet Binns Igor V. Moskalenko Ge/ Ge Ge/ Ge 69 Ga/ Ga Ge/ Ge Ni/ Ni Ni/ Ni Cu/ Cu Zn/ Zn Zn/ Zn Fe/ Fe Ni/ Ni Ni/ Ni Fe/ Fe 56 Fe/ Fe Mg/ Mg Si/ Si Si/ Si S/ S Mg/ Mg 24 Na/ Mg C/ O N/ O N/Ne Ne/ Ne C/ C 0.25 Why Wolf-Rayet material is so important?

29 Schematic OB association timeline Binns Igor V. Moskalenko 29

30 Elemental Abundances relative to 80/20 mix of SS and massive star outflow (MSO) Elemental Abundances relative to SS only TIGER+HEAO-3 data TIGER+HEAO-C2 data Ga Sr Co 1 Refractories GCRS/Lodders-SS Ca Mg Si Fe Ni Cu P Se Al Zn Ne Volatiles S Ar Ge N Atomic Mass TIGER-LDB/Meetings/COSPAR-2010/100-0 mix_tiger_bobs_fits Rauch Igor V. Moskalenko 30

31 Same dependence at TeV energies ACE/CRIS CREAM Ahn Rauch Igor V. Moskalenko 31

32 Backup slides Igor V. Moskalenko 32

33 THANKS TO EVERYBODY AND ESPECIALLY TO GUESTS WHO MADE IT TO STANFORD! Igor V. Moskalenko 33

34 First Ionization Potential (FIP) vs. Volatility Rb Cs Na K Cu Ga Ge Se Zn Pb ~104 K Low-FIP ~ Refractories Rb, Cs break the rule Other important elements: Na, Cu, Zn, Ga, Ge, Pb Meyer, Drury, Ellison 1997 Igor V. Moskalenko 34

35 Rauch Igor V. Moskalenko 35

36 Measured isotopic abundance ratios compared to Solar System Abundances (Lodders, 2003) 1.2 Ratio SS(Lodders) 1.0 Cu Zn Ga Ge 0.8 Ratio Abundances corrected for 0.6 nuclear interactions in instrument Energy intervals Abundances include first order leaky box propagation back to the source /63 66/64 68/64 70/64 71/69 70/74 72/74 76/74 7_29_11_ICRC-Isotope_corrections/Isotope_ratio_figure.opj 36 36

37 Comparison with 80%/20% mix of Solar System and WR material Ratio SS(Lodders) 80%/20% SS/WR mix Cu Zn Ga Ge Ratio For these isotope ratios, the 80/20 mix is very similar to pure SS, within the accuracy of our measurement Measured ratios are consistent with either pure Solar System or an 80/20 mix of SS and massive star ejecta /63 66/64 68/64 70/64 71/69 70/74 72/74 76/74 7_29_11_ICRC-Isotope_corrections/Isotope_ratio_figure.opj 37 37

38 Elemental Abundances Relative to Fe Abundances at the top of the atmosphere Relative Abundance (Fe=1) 1E-3 Correction factors for saturated pulse heights at high-z: ACE HEAO-C2 TIGER Solar System (LPK 2009) Z 1E-4 1E-5 Corr E _2_11-Element ICRC paper/abund_rel_fe_ace_tig_heao Charge (Z) 38

39 Binns Ge/ Ge Ge/ Ge Ga/ Ga Ge/ Ge 71 Ni/ Ni Ni/ Ni Cu/ Cu Zn/ Zn Zn/ Zn 62 Fe/ Fe Ni/ Ni Ni/ Ni Fe/ Fe Fe/ Fe 5 54 Mg/ Mg Si/ Si Si/ Si S/ S Mg/ Mg Na/ Mg 23 C/ O N/ O N/Ne Ne/ Ne 12 C/ C 13 Ratio Relative to Solar System Abundances In Context of Previous Data at Lower Charge 6 WR Model CRIS data (Binns et al. 2005) Combined data corr for volatility New CRIS UH-Isotopes

40 Elemental Abundances relative to 80/20 mix of SS and MSO Elemental Abundances relative to SS only TIGER+HEAO-3 data TIGER+HEAO-C2 data Ga 1 Mg Si GCRS/Lodders-SS Refractories Fe Ni Cu P Se Al Zn Ne Volatiles S Ar Ge N GCR Source/(80% SS + 20% MSO) (Fe=1) Sr Co Ca TIGER Vol (gas) TIGER Ref (grains) HEAO-C2 Vol HEAO C2 Ref HEAO C2-Mixed Vol & Ref ACE-Volatiles ACE-Refractories 1 Refractory Sr Ni Si Atomic Mass Ga Se P Mg Al TIGER Zn S N O Cu Volatile ACE Fe Ca Ar Ge Ne Atomic Mass (A) TIGER-LDB/Meetings/COSPAR-2010/100-0 mix_tiger_bobs_fits 8_2_11-Element ICRC paper/spirce_gcrs_vs_mass_80-20.opj 40