Extragalactic Jets and GLAST Łukasz Stawarz KIPAC, 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) B GB z = 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. size: ~2.5 Mpc

Why are they so interesting (II) (Komissarov) (Hawley & Krolik) 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)

Why are they so interesting (III) Jets are strictly connected with the evolution of galaxies / clusters of galaxies. They may be key players in shaping such evolution, since total energies transported by jets can be huge: L jet ~ erg/s, t life ~ 10 7 yrs, i.e. E tot ~ 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 eV energies, and are claimed to accelerate protons up to the highest observed energies ≥10 20 eV. Mrk 501 Centaurus A (Blandford, Petrosian, Reimer, Stawarz) shocks?

Why is it so difficult to understand jets (I) Huge range of jet parameters (L jet ~ erg/s, D j ~ 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 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. 3C 120 (collaboration with a number of radio people)

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. λ e ~ c/ω e ~ 10 8 (n e /10 -3 cm -3 ) -1/2 [cm] r g ~ E e /eB ~ (γ/10 8 ) (B/10 -4 G) -1 [cm] R j ~ [cm], D j ~ [cm] 3-D HD, PIC simulations (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-rays PKS 2155 TeV γ-rays (H.E.S.S.) Extragalactic jets are characterized by the extremely variable broad-band emission (t var ~ 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?