Lunch discussion on motivations for studying blazar variability Greg Madejski, SLAC

1. Lunch discussion on motivations for studying blazar variability Greg Madejski, SLAC Parts of this presentation use slides by Benoit Lott and Jun Kataoka * Introduction and general comments: * “Blazar” is a phenomenological term, defined by observational characteristics * Variability over ALL energy bands is a defining property of blazars * Other characteristics include: * compact radio source (not always resolved, even via radio interferometry) * polarization in radio through optical * appearance of a large-scale jet in radio, opt., X-ray • * many blazars show that they are hosted in galaxies (but galaxy is not always detected) • * Variability holds a promise to understand the blazar phenomenon • * Best model (“paradigm”) has the blazar emission originating • in relativistic jet, pointing close to our line of sight * Relativistic motion of the jet Doppler-boosts the emission in the direction of motion • * Within this, “misdirected blazars” are probably radio galaxies • (generally, much more numerous in the Universe) • * For the purpose of this discussion: blazars are strong and variable g-ray emitters, and • correlation of variability patterns should shed light on the origin and structure of the jet

2. Radio, optical and X-ray images of the jet in M 87 * Jets are common in AGN – and radiate in radio, optical and X-ray wavelengths * Blazars are the objects where jet is pointing close to the line of sight * In many (but not all) blazars, the jet emission dominates the observed spectrum

3. Unified picture of active galaxies Diagram from Padovani and Urry

4. EGRET All Sky Map (>100 MeV) 3C279 Cygnus Region Vela Geminga Crab PKS 0528+134 LMC Cosmic Ray Interactions With ISM PSR B1706-44 PKS 0208-512

5. Evidence for beaming Simple light travel argument relates the emission size scale to the variability time scale Source “compactness” (old radio astronomy arguments) if the source is as small as variability scales indicate, particle and photon energy are v. high -> the radiative losses due to Compton emission would be prohibitive - violation ⇒beaming Elliot Shapiro relation assume stationary emission, Eddington-limited flow Dt > Rs/c ~ 103 M8 s LEdd =1.26 1046 M8 erg s-1 L / Dt < 1043 erg s-2violation ⇒beaming Gamma-ray transparency (to e+/e-pair production) R < cdDt/(1+z) if X-rays are produced in the same region as g-rays tgg >> 1 ⇒ beaming Magnetic field limits (Catanese 1997) (somewhat model dependent) Correlated variability between optical/X-ray and GeV/TeV (EsyndDt)-1/3 < B < Esynd /Ec2 violation ⇒beaming

6. Blazars are variable in all observable bands

7. Blazar models There is such a thing as a “standard model” for blazars (well, one “standard” and one “competing” model) Standard (leptonic) model Photons are produced by energetic electrons low energy peak is produced by synchrotron emission, high energy peak is due to Compton emission both due to non-thermal population of relativistic electrons, synchrotron peak – particle interaction with B field, Compton peak – particle interaction with ambient photon field Competing (hadronic) model Protons are accelerated, lose energy mainly due to p-p or p-g interaction, produce pions, … Both models require acceleration of particles to very high energies (we now little about it!) BUT ALL MODELS INVOKE RELATIVISTIC JET – INDEPENDENTLY, “BULK” ACCELERATION IS MOST LIKELY REQUIRED

8. Two examples of blazar spectra

9. blazar variability: what can we learn? • Variability time scale: origin of flares constraints on source size ⇒ beaming tests, bulk motion identification of source as a blazar • Correlated variability - time lags: acceleration/ deceleration processes source geometry (one zone…) importance of external fields: disk, BLR, torus jet matter content (e+/e- vs p+/e-) • Loop diagrams (flux vs index): acceleration/ deceleration models, SSC vs ERC models • “Orphan” flares - anomalous components: test of SSC models jet matter content (e+/e- vs p+/e-) UHECR acceleration? • Radio knot ejection after GeV flares?: jet launching sites, jet acceleration/deceleration • X-ray precursor: jet matter content (e+/e- vs Poynting flux, p+/e-), jet environment • Correlated variability in different bands: counterpart association • Steady component: distinction between inner jet and extended Chandra jets

10. G 1+2 G1 G2 from Jun Kataoka What makes a rapid variability ? X-ray/g-rays BLR cloud BLR cloud 1016-17cm (sub-pc) G1 G2 • Assume that the central BH mass is108-9 M and10rg = 1014-15cm. • Modulation of relativistic flows - faster shell (G1) catches up with the • slower one (G2) at D~ 10 G1+2 2 rg ~ 1016-17[cm] • e-e+ (and possibly smaller fraction of p ) are accelerated in the shock, • and emit Sync/ inv Comp radiation. • Similar to the GRB prompt emission, but tacc ~ tcool ≲R/ dvshock ~ 1 day.

11. daily flares - only visible at the LE/HE peak. - changes in acceleration eff. “steady” component - commonly observed in all freq. - changes in the mass acc rate ? from Jun Kataoka Flare and Quiescent ? -1 2D0 1 1 G1 • flare duration : tcrs ~ c G1+22 G1+22 G22 G2 • internal E: Em ~ Mc2 (G1 + G2 -2G1+2) gmax   • Max electron E: vs/c G1+2 = (G1G2)1/2 D-1 • If DG ( G1 - G2)is large, collision takes place at small distances, with large/short variability. significant increase in gmax JK+ 2001; Tanihata+ 2003 • If DGis small, collision at large distance, with only small variability. 1day Mrk 421 Mrk 501

12. from Jun Kataoka Soft-Xray flare (bulk Compton) Gfast Gslow g-ray flare soft-X (fast) g-ray flare (int. shock) soft X (slow) Soft X-ray “precursor” before the GeV flare? • “Seed” for the ERC process is UV photons reflected by the BLR. • Ediff ~ 10 eV, Ldiff ~ 1046 erg/s • Before the collision, both the fast and slow shells upscatter UV photons • via the “bulk-Comptonization” to EBC ~ GBLK2Ediff~ 1 keV. • After the collision, g-rays are emitted via the ERC process, peaking at • EERC ~ gp2 Ediff ~ 1GeV(gp ~ 104 for shock accelerated electrons) Moderski+ 2004 Broad Line region

13. from Jun Kataoka pure e-e+ Matter content of the jet? • Such scenario, however, assumes cold pair plasma (e- e+) as • a matter content of jets. • If significant protonsare involved, such precursor will not be observed. • Absence of “bump” feature? →Ne/Np < 50? • Also, “no precursor” may imply that g-ray flares are produced by • reconnection events rather than by internal shocks. • jets at pc-scale are still dominated by B-field??? Collaboration with SWIFT and Suzaku will Clarify this further ! Sikora et al. 1994 Sikora & Madejski 2000

14. from Jun Kataoka t=0 of radio -knot ejection EGRET radio Radio knot ejection after GeV flare (QHBs) ? • Radio-knots in QHBs often shows super-luminal motion; vapp /c ~ 10. • Jet is highly relativistic even on pc-scale, at least in QHBs • g-ray flares were followed by the appearance of new radio-knots. • g-ray events “trigger” the ejection of radio-knots? key to understanding launching site of the jets ! Jorstad et al. 2001a, b

15. Tests of the Compton-scattered CMBR interpretation of extended X-ray jets PKS 0637-752 X-ray (Chandra) +optical Radio map + fractional polarization

16. GLAST LAT’s ability to measure the flux and spectrum of 3C279 for a flare similar to that seen in 1996 (from Seth Digel) The picture on the left leads to Benoit’s presentation: GLAST’s improvement in variability studies over EGRET goes only as the ratio of effective areas * In summary, to learn about the structure of blazars, origin of relativistic jets, acceleration and radiation processes, g-ray variability must be studied in the Context of as many bands as possible! * Most other bands study objects “one at a time”– we will need lots of resources