Astroparticle physics

2. The Milky Way interstellar medium and cosmic-rays

Alberto CarramiñanaInstituto 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.

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, H2, 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 106 M, 50 pc

• GMC cores : 100 to 200 K, 107 to 109 cm-3, 10 to 1000 M, 0.05 to 1 pc.

– Bok globules : 10 K, n>104 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 1011 of them in the Milky Way (Mg > 1.5 1011 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

CO@2.6mm

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 ucr 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 3G)

• Transport equation:– Leaky box model:

• CR travel path:

• Proton injection spectrum:

– 10Be (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<1015 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 = 31015 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

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 = 1045 g/cm2

Pulsar energetics: the Crab

Pulsars

• >1000 radio pulsars know

• Power: up to few 1038 erg/s (Crab) per pulsar vs 2 1040 erg/s (CRs) Probably sufficient

• Pulsar models: pure electron acceleration– in vacuum: 1016 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 1015 eV (the knee)

• At 100 TeV gyro-radius thickness of Galactic disc.

• To continue...