Astroparticle physics 2. The Milky Way interstellar medium and cosmic-rays Alberto Carramiñana Instituto Nacional de Astrofísica, Óptica y Electrónica Tonantzintla, Puebla, México Xalapa, 3 August 2004

These presentations Available (soon!) as  alberto/cursos/ap2004_1a.ppt  alberto/cursos/ap2004_1b.ppt  alberto/cursos/ap2004_2.ppt  alberto/cursos/ap2004_3.ppt  alberto/cursos/ap2004_4.ppt

The interstellar medium of the Galaxy ISM: gas, dust, magnetic field, cosmic-rays. Feedack: {gas (SF)  stars (Winds, Sne)  gas} Stars enrich (& steer) gas; gas forms new stars. Pressure equilibrium. GCDisk Halo 15 kpc 300 pc

A little note: Oort’s limit Statistical study of motion of stars in the Solar neighborhood: first evidence of “missing mass”. Can be baryonic (or it can be non-baryonic...).

ISM clouds Most of the ISM (70%) is HI, H 2, HII: –diffuse HI clouds: 30 to 80 K, 100 to 800 cm -3, 1 to 100 M . –translucent molecular clouds: 15 to 50 K, 500 to 5000 cm - 3, 3 to 100 M , several pc accross. –giants molecular clouds: 20 K, 100 to 300 cm -3, up to 10 6 M , 50 pc GMC cores : 100 to 200 K, 10 7 to 10 9 cm -3, 10 to 1000 M , 0.05 to 1 pc. – Bok globules : 10 K, n>10 4 cm -3, 1 to 1000 M , 1pc, (all?) harbour young stars in their center. –HII regions: ionized by massive near star.

Dark clouds Brighter cloud!

Stars About of them in the Milky Way (M g > 1.5  M  ). Form, live and die: –M<8 M  : pufff... –M>8 M  : bang! –M>30 M  : bang!? pufff? bang!!? SN 1987A

Stellar remnants Planetary nebula + white dwarf: –Vexp  100 km/s Supernova remnant (SNR) + neutron star: –Vexp > 1000 km/s

E  1 keV

At 408 MHz

Cosmic-rays Energetic particles in Earth’s environment Basic questions: –Energy? –Composition? –Origin? –Isotropy?

Cosmic-rays: measured abundances Charged particles: 99% nuclei + 1% electrons. Heavy nuclei more abundant in CRs than solar. {Li, Be, B} and {Sc, V, Ti,...} high C/O and Fe spallation Cross sections spallation  X = 5 to 10 g cm -2  L  1000 kpc

Cosmic-rays: energy spectrum Power-law: Secondaries (B) have steeper spectra than primaries (C,O).

Cosmic-rays: energy density Local ISM Spectrum inferred u cr  1eV cm -3 (0.83 for p alone) CR and Galactic energetics: Are SN the sources of (Galactic) CR? –Shock acceleration models: Fermi mechanism ok! –Need the smoking gun...

Cosmic-rays: propagation Cosmic-rays do not propagate in straight lines: trapped by Galactic magnetic field (average 3  G) Transport equation: –Leaky box model: CR travel path: Proton injection spectrum: – 10 Be (mean life 3.9 Myrs) analysis: (Garcia-Muñoz, Mason & Simpson 1977)

Galactic radio emission Galactic radio emission = e-synchrotron Inferred electron spectrum: 1 eV cm -3 –n(E)  E for 70 MeV to 1200 MeV –n(E)  E -3.0 above 1 GeV Electrons 1% of Earth’sCR spectrum.

Cosmic-ray nuclei and matter Galactic  -ray emission model: –e-bremssthralung –pion production (secondary e produced) –e-inverse compton Model needs HI & CO data input. Hunter et al. 1997

Galactic  -ray spectrum  0 production spectrum  68 MeV bump Galactic emission fairly well modelled. Evidence for electrons and nuclei. Strong, Moskalenko & Reimer 2004

Nearby galaxies Only LMC detected as (weak)  -ray source. Limits on SMC, M31, nearby starburst  cosmic- rays (E<10 15 eV) are Galactic (local).

Cosmic-ray and  -ray sources High energy sources must accelerate particles to produce  -rays.

Galactic  -ray sources Solar flare Pulsars (aside: bound on photon mass) Unidentified Galactic sources: young & old –SNR positional coincidences (so, maybe....) –young & old radio quiet pulsars –wind nebulae –microquasars

Photon mass Crab pulsar pulse coherent from (at least) 100 MHz to 1 GeV. Pulse period = 33 ms. Pulse broadening < 5% Distance = 2 kpc(1 pc = 3  m) What is the limit on the mass of to photon?

Cerenkov observations Certain detection of Crab nebula. Probable PSR , Vela, SN1006. Results not fully consistent (Č to Č, Č to EG) Weekes (2000)

Crab spectrum Kuiper et al. (2001) Nebula: can fit synchrotron + inverse Compton. Pulsar: syncrotron + curvature + inverse Compton.

Rotating neutron star: R * =10 km, M * =1.44 M , I = g/cm 2 Pulsar energetics: the Crab 

Pulsars >1000 radio pulsars know Power: up to few erg/s (Crab) per pulsar vs 2  erg/s (CRs)  Probably sufficient Pulsar models: pure electron acceleration –in vacuum: eV available; –in e + e - magnetosphere: only a “fraction” Romani 1994

What do we need? The hadronic  0 smoking gun! And GLAST

Very high energy cosmic-rays Pulsar and Sne models can only reach eV (the knee) At 100 TeV gyro-radius  thickness of Galactic disc. To continue...