Extragalactic Jetsand GLAST

Łukasz StawarzKIPAC, Stanford University

Outline

1. What are extragalactic jets?2. Why are they so interesting?3. Why is it so difficult to

understand them?4. Why do we need GLAST?

What are extragalactic jets?Jets are extremely well

collimated streams of magnetized collisionless plasma emanating from the centers of active galactic nuclei (AGNs), and propagating with relativistic bulk velocities up to kpc/Mpc distances.

Although widely studied at different frequencies (from low-frequency radio up to very high γ-ray photon energies) they are still superficially understood objects.

First jet ever detected:M 87 (Curtis, 1918)

Why are they so interesting (I)

(Cheung,Stawarz)

B0925+42 GB 1508+5714

z = 4.3

1745+624z = 3.89

Extragalactic jet are the largest structures in

the Universe, reaching even Mpc scales. They are

being found everywhere up to the highest redhsifts.

size: ~

2.5

M

pc

Why are they so interesting (II)

(Komissarov)(Hawley & Krolik)

Jets are produced by rapidly rotating supermassive (~ 106-109 M⊙) black holes surrounded by magnetized accretion disks. Thus, jets are direct probes

of black hole physics.(Blandford, McKinney)

Why are they so interesting (III)

Jets are strictly connected withthe evolution of galaxies /

clusters of galaxies. They may be key players in shaping suchevolution, since total energies transported by jets can be huge:

Ljet ~ 1047 erg/s, tlife ~ 107 yrs, i.e. Etot ~ 1062 ergs .

Cygnus A

(Allen, Madejski)

Perseus A

Why are they so interesting (IV)

Jets are extremely efficient accelerators of particles to

ultrarelativistic energies. They are known to produce electrons with 1014

eV energies, and are claimed to accelerate protons up to the highest

observed energies ≥1020 eV .

Mrk 501Centaurus A

(Blandford, Petrosian, Reimer, Stawarz)

shocks?

Why is it so difficult to understand jets (I)

Huge range of jet parameters(Ljet ~ 1038-1048 erg/s, Dj ~ pc-Mpc),

huge variety of jet morphologies,huge variety of jet spectra.

(Cheung, Costamante)

Why is it so difficult to understand jets (II)

Jets are strictly relativistic phenomena. They areproduced in a strong gravitation field of SMBHs,and propagate with highly relativistic bulk velocities (3 ≤ Γ ≤ 30). Special relativistic effectssuch as beaming, light aberration, time contraction, and the Doppler frequencyshift, shape their observed properties.

3C 120

(collaboration with anumber of radio people)

Why is it so difficult to understand jets (III)

Jet plasma is collisionless: all the interactions of particles are mediated by themagnetic field. In addition, jets are highly supersonic relativistic outflows, and

hence one expects formation of strong relativistic shocks and turbulence.Understanding multi-scale structure of the jet plasma and jet magnetic field is

extremely difficult, and cannot be fully addressed (yet?) by numerical simulations.

λe ~ c/ωe ~ 108 (ne/10-3cm-3)-1/2 [cm]rg ~ Ee/eB ~ 1015 (γ/108) (B/10-4G)-1 [cm]Rj ~ 1015-1022 [cm] , Dj ~ 1016-1024 [cm]

3-D HD, PICsimulations(MHD, GRMHD,in progress)

(Abel, Spitkovsky)

Why do we need GLAST (I)Despite 40 years of extensive investigations, many key questions

regarding extragalactic jets remain open:• Jet composition (B and ultrarelativistic e-e+; something else?)• Jet magnetic field (how strong? what is its structure?)• Jet launching (rotating SMBHs vs accretion disks)• Jet evolution and energetics (kinetic power, lifetimes, „feedback”)• Particle acceleration (shocks? turbulence? reconnection?)

Limitations of theoretical and numerical approaches can be partly overcome by multiwavelength observations.

• Radio: VLBI, VLBA, VLA, several planned instruments• IR-UV: Spitzer Space Telescope, Hubble Space Telescope, several

ground-based instruments• X-rays: Chandra X-ray Observatory, XMM Newton, Suzaku, Swift,

several planned missions• GeV γ-rays:

………………………………………………………………………………………..………

• TeV γ-rays: H.E.S.S., Magic, CANGAROO, Veritas, planned large-array systems (CTA)

Why do we need GLAST (II)

EGRET on board of Compton Gamma-Ray Observatory has

detected tens of jetted AGNs, however only the brightest

small-scale ones („blazars”), and only during their flaring states. Nevertheless, EGRET observations

revolutionized our understanding of extragalactic jets: • bulk of the radiated jet power at γ-rays !• extreme variability on very short timescales !

>150 EGRET blazars (Romani)

Why do we need GLAST (III)

OJ287: optical

Mrk 421: X-raysPKS 2155TeV γ-rays(H.E.S.S.)

Extragalactic jets are characterized by the extremely variable broad-band emission (tvar ~ 200 s at TeV energies).

With GLAST, we can think for the first time about long, truly

multiwavelength campaigns for a large number of sources.

(Carson, Chiang, Madejski, Paneque, Reimer, Romani)

What do we expect from GLAST

GLAST is expected to detect several thousands of extragalactic jets. In addition to flaring blazars, also large-scale (> kpc) jet structures and quiescent levels of emission are expected to be studied.

By means of investigating jet variability and spectra at „crucial” GeV photon energy range, GLAST will hopefully provide some answers to the long-standing questions regarding these most extreme manifestations of the black hole activity:

Where is bulk of the jet energy dissipated? Do the extragalactic jets contain protons? (UHECRs?) How strong is the jet magnetic field? What accelerates jet particles to ultrarelativistic

energies?