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 http://www.inaoep.mx/  alberto/cursos/ap2004_1a.ppt http://www.inaoep.mx/  alberto/cursos/ap2004_1b.ppt http://www.inaoep.mx/  alberto/cursos/ap2004_2.ppt http://www.inaoep.mx/  alberto/cursos/ap2004_3.ppt http://www.inaoep.mx/  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. Halo 300 pc Disk GC 15 kpc

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 : 0.05 to 1 pc.

100 to 200 K, 10 7 to 10 9 cm -3 , 10 to 1000 M  , – 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 10 11 (M g of them in the Milky Way > 1.5  10 11 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

[email protected]

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   L  1000 kpc X = 5 to 10 g cm -2

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 -2.14

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  10 15 m) • What is the limit on the mass of to photon?

Cerenkov observations • Certain detection of Crab nebula.

• Probable PSR 1706 44, Vela, SN1006.

• Results not fully consistent (Č to Č, Č to EG) Weekes (2000)

Crab spectrum • Nebula: can fit synchrotron + inverse Compton.

• Pulsar: syncrotron + curvature + inverse Compton.

Kuiper et al. (2001)

Pulsar energetics: the Crab • Rotating neutron star: R * =10 km, M * =1.44 M  , I = 10 45 g/cm 2 

Pulsars • >1000 radio pulsars know • Power: up to few 10 38 erg/s (Crab) per pulsar

vs

2  10 40 erg/s (CRs)  Probably sufficient • Pulsar models: pure electron acceleration – in vacuum: 10 16 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 10 15 eV (the knee) • At 100 TeV gyro-radius  Galactic disc.

thickness of • To continue...