1. Extragalactic Jets and GLAST
Łukasz Stawarz
KIPAC, Stanford University

2. Outline What are extragalactic jets? Why are they so interesting?
Why is it so difficult to understand them?
Why do we need GLAST?

3. 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)

4. Why are they so interesting (I)B GB
z = 4.3
size: ~2.5 Mpc
(Cheung,
Stawarz)
z = 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.

5. Why are they so interesting (II)
Jets are produced by rapidly rotating supermassive (~ M⊙) black holes surrounded by magnetized accretion disks. Thus, jets are direct probes of black hole physics.
(Blandford, McKinney)
(Komissarov)
(Hawley & Krolik)

6. Why are they so interesting (III)
Jets are strictly connected with
the evolution of galaxies and of
intergalactic medium. They may
be key players in shaping such
evolution, 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

7. 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 .
(Blandford, Petrosian, Reimer, Stawarz)
Centaurus A
Mrk 501

8. Why is it so difficult to understand jets (I)
Huge range of jet parameters
(Ljet ~ erg/s, Dj ~ pc-Mpc),
huge variety of jet morphologies,
huge variety of jet spectra.
(Cheung,
Costamante)

9. Why is it so difficult to understand jets (II)
Jets are strictly relativistic phenomena. They are
produced in a strong gravitation field of SMBHs,
and propagate with highly relativistic bulk
velocities (3 ≤ Γ ≤ 30). Special relativistic effects
such as beaming, light aberration, time contraction,
and the Doppler frequency
shift, shape their observed
properties.
(collaboration with a
number of radio people)
3C 120

10. Why is it so difficult to understand jets (III)
Jet plasma is collisionless: all the interactions of particles are mediated by the
magnetic 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 ~ [cm] , Dj ~ [cm]
3-D HD, PIC
simulations
(MHD, GRMHD,
in progress)
(Abel, Spitkovsky)

11. 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)

12. 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)

13. Why do we need GLAST (III)
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.
OJ287: optical
(Carson, Chiang, Madejski, Paneque, Reimer, Romani)
PKS 2155
TeV γ-rays
(H.E.S.S.)
Mrk 421: X-rays

14. We need 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 products 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?