BL LAC OBJECTS

Marco Bondi

INAF-IRA, Bologna, Italy

A “beamed” review

This review includes:

Recent (2-3 years) developments on a few selected

topics.

This review will NOT cover:

Polarization properties

Parent population of BL Lacs and unified schemes

Outline

The Blazar family

New samples of BL Lacs

Pc-scale kinematics

Broad-band correlations

Future developments

The Blazar Familye.g. Urry & Padovani '95

SED dominated by sync and

IC processes from radio to

gamma-ray.

Flat radio spectra, extreme

variability, high polarization

(radio & optical), different opt

spectroscopic properties.

Unified scheme: BL Lacs as

low luminosity blazars.

New samples of BL Lacs:

why we need them ? The starting point: the “blazar sequence” (Fossati

et al.1998)

HBL, LBL, FSRQ

Warning !!! Based on 3 highly

biased samples

lack of : low power low-energy peaked obj high power high-energy peaked obj

New samples of BL Lacs: testing the blazar sequence with CLASS

The CLASS Blazar Sample (Caccianiga & Marcha '04): 300 flat spectrum, > 30 mJy, sources.

Motivation: looking for weak X-ray emitter BL Lac, i.e.

steep radio-to-X-ray spectral index.

Results: a significant and large fraction of low luminosity

blazars in the sample lie outside the blazar sequence

See also H. Bignall's talk.

New samples of BL Lacs:

HST and VLBI obs of nearby objectssee M. Giroletti poster

Nearby (z<0.2) BL Lacs from the HST snapshot

image survey (Giroletti et al. '06).

Core dominance, jet/counter-jet ratio, SSC

models used to constrain beaming parameters:

Г ~ 4

Common origin for radio and optical “core” emission

AGN Jets: the fundamental questions modified from Lister '03

AGN jet speed distribution:

fast or slow jets ? what is the maximum jet speed ?

Velocity profile:

radial: decelerating jets ?

transverse: spine & layer ?

Relation of jet speed to other AGN properties:

dependence on BH mass ? optical class ?

are more luminous jets faster ?

which AGN have fastest jets ?

Jet speed distribution

Jorstad et al. 2005:

7mm, 17 epochs,

Some of the most

extreme values

confirmed (e.g. Piner

et al. '06)

Pc-scale kinematics: TeV sources Jet motions in TeV BL Lacs (Piner & Edwards

'04): multi-epoch 15 Ghz observations

TeV BL Lacs: pc-scale kinematics

Jet motions in TeV BL Lacs (Piner & Edwards

'04): multi-epoch 15 Ghz observations

Similar jet morphologies: collimated, bending,

transition to diffuse emission (see also Rector,

Gabuzda & Stocke '03)

Components in TeV BL Lacs are predominatly

stationary or subluminal: Г ~ 2-4 (also Giroletti

etal '04)

TeV BL Lacs: radio and gamma ray

beaming factors Г(VLBI)~2-4 Г(SED,gamma-ray)~10-50

Jet velocity structure

Radial: strong deceleration (Georganopoulos & Kazanas '03)

Transverse: fast spine and slow layer (Ghisellini et al '05)

one component sees the beamed radiation produced

from the other and this yields to enhanced gamma-ray

emission.

TeV BL Lacs: radio and gamma ray

beaming factors

Conical jet model (Gopal-Krishna et al. '06):

each element of the jet cross section is boosted

by a different amount because having different

misaglinement. The inferred Г are

underestimated.

Coordinated broad-band campaigns:

radio-optical Whole Earth Blazar Telescope (WEBT) campaigns

provided an unprecedented time sampling for radio and

optical light curves:

BL Lac (Bach et al. '06)

3C 66A (Bottcher et al. '05)

0235+164 (Raitieri et al. '05)

Major optical bursts linked to flux density and polarisation

variations in the VLBI core with no apparent changes in the

VLBI jet. Confirmed in OQ530 (Massaro et al. '04)

WEBT Campaigns on BL LAC itselfBach et al. '06

10 years optical and VLBI monitoring.

VLBI allows to disentangle the different

components contributing to the single dish radio

light curves.

Results:

spectral variability in the single-dish data traces the

variability of the VLBI core.

fair correlation (time delay between 50-150 days)

between variations in the optical and radio band.

Coordinated broad-band campaigns:

radio-gamma-ray Connection between gamma-ray outbursts and

the ejection of VLBI components have been

found (Pohl et al. '95, Jorstad et al. '01, Lähtenmäki &

Valtaoja '03).

Correlated radio and TeV variability in Mkn 421

investigated by Charlot et al. 06:

variations on few weeks timescale in the VLBI core

no significant variations in the VLBI jet

Future: AGILEhttp://agile.rm.iasf.cnr.it

Gamma-ray (30 MeV-30

GeV) and hard X-ray (15-

45 keV) imaging

Consortium of Italian

partners

Launch 2007

AGILE gamma ray detector

Source location determination:

5-20 arcmin (about twice better than EGRET)

Sensitivity:

comparable to EGRET on-axis, better for off-axis

FOV:

3 sr, about 6 times EGRET's

sensitivity for a 1-year all sky survey 3 times better than

EGRET

Broad-band monitoring of AGNs