Direct imaging of AGN jets and black hole vicinity Tiziana Venturi Active Galactic Nuclei 9 Ferrara,

Radio VLBI as the most direct way to look into the inner regions of AGNs Knowledge of the inner jets in AGN even more relevant these days due to the current γ -ray observatories: true simultaneous radio/ γ -ray studies of correlated variability, essential to locate the γ -ray emission. Current hot VLBI studies of AGNs - Simultaneous radio/ γ –ray monitoring (radio imaging) of flaring blazars - The very faint Universe: low power nearby AGN (see Giroletti) & powerful high-z quasars z=0.01 -> 1 mas = 0.2 pc z=0.1 -> 1 mas = 1.8 pc z=2 -> 1 mas = 8 pc

Unified view of Radio Loud AGN Low power FR I and BL Lacs High power FR II and FSRQ Unification models (Orr & Browne 1982; Urry & Padovani 1995) successfully tested in the radio band for the two power ranges : viewing angles and intrinsic relativistic speeds at the jet base

AGNs all very similar from a morphological point of view when looked on the parsec-scale: mostly core-dominated with an asymmetric jet, regardless of the classification (radio galaxies, BL Lacs, FSRQ) Orientation and relativistic velocities at the jet base Markarian 421 – Blue BLBL Lac – Red BL3C FSRQ Cygn A - FRII M87 - FRI Images from MOJAVE at 15GHz Mkn 421 BL Lac 3C454.3 M87 Cygnus A

Sample of low/intermediate power radio galaxies (Giovannini et al. 2001) Sample of neraby BLLacs (Giroletti et al. 2004) Consistency in the distribution of Lorentz factors

Sample of low power radio galaxies (Giovannini et al. 2001) Sample of nearby BLLacs (Giroletti et al. 2004) Distribution of viewing angles consistent with the idea that the two classes of radio sources belong to the same population of objects seen under differentangles to the line of sight

The nuclear radio properties of highly beamed sources The Blazar World When we look at the powerful radio sources aligned at small angles to the line of sight, the most extreme properties are found: -Strong flux density variability -Morphological changes implying superluminal speeds -Instabilities in the radio jet Observer

Flux density variability Venturi et al & 2003 Expanding cloud of relativistic electrons initially thick at some frequencies and viewed very close to the line of sight

PKS HPRQ; z=0.36 βapp= 23.76c BLLac; z= βapp= 10.57c C454.3 HPRQ; z=0.859 βapp= 14.19c Structural variability and superluminal motion Favourable viewing angle and high intrinsic speed of the radio emitting plasma, lead to superluminal proper motion Polarization and total intensity movies from MOJAVE

3C279 VLBA 43GHz HPRQ, z=0.536 β app = 20.57c Radio galaxy, z=0.033 β app = 5.43

Current studies. I. Statistics from the MOJAVE survey The sample & the project - Nearly 300 compact AGN in the Northern Sky, 135 of which form a complete flux density limited sample (δ > -20 o, S 2cm > 1.5 Jy at any epoch between 1994 and 2004) - Monitoring carried out with the VLBA at 2 cm starting from Statistical analysis made on the basis of the original sample: 135 sources 526 separate features in 127 jets (no speed measurements for 8 sources) database consisting of 2424 images Ideal band: high angular resolution, very good image sensitivity and better reliability compared to BU monitoring

Analysis carried out for BL Lacs, FSRQ and radio galaxies separately (Lister et al. 2009) Fastest component moving at 50.6c and interpreted as the upper end of the AGN jet Lorentz factor distribution Peak at ~ 10c Apparent velocity vs redshift: the distribution is not the result of observational limitations

Locus of (β app,L) for sources with γ=32 and L=10 25 W/Hz VLBA observational limit set at S=0.5 Jy and μ=4 mas/yr Radio galaxies BL LacsQuasars

Before the advent of AGILE, FERMI and ground-based new VHE observatories,only a handful of simultaneous multiband campaign carried out on the best known blazars (i.e. 3C279, Mrk 421 …) with a variety of results (Hartmann et al. 2001; Blazejowski et al. 2005), or a posteriori correlations (Jorstad et al. 2001) Current studies. II. Simultaneous radio/ γ -ray monitoring with VLBI imaging radio γ -ray γ- ray flare Superluminal ejection

PKS (Marscher et al. 2010) VLBA 43 GHz monitoring & Fermi LAT and AGILE observations Optical and γ -ray flares in good coincidence Rotation of the optical polarization vector 2 new superluminal features with speeds of 24±2 c and 21.6±0.6 c Multiband observations interpreted as a single feature (seen as superluminal) moving through a helical magnetic field in the jet acceleration zone

3C454.3 (Vercellone et al. 2010) VLBA 15 GHz monitoring & AGILE observations 15 GHz - 7 Aug 2007 Total flux density increase due to the radio core (component C) Flux density of the main jet components stable or decreasing No proper motion along the jet No birth of new components so far From the core variability at 43 GHz it was derived that the source is viewed at θ~1.5° and that Γ~20 Flares in the optical and γ -ray band Slow monotonic flux density increase at radio wavelengths

The case of M87 (Giroletti et al. 2010) Coordinated radio-VHE (VERITAS) observational campaign VHE flares on 9/2/2010 and April 2010 Second radio galaxy, beyond 3C84, detected at high energies

ATel #2431 – VHE flare on 9 Feb 2010 eVLBI monitoring – 2 epochs before the flare and 4 during and after the flare Inner jet HST-1 Evidence for flux density increase at the jet base (~10%) and continued proper motion in HST-1 with v app ~ 7c

VLBI results: EVN detection rate 100% at 1.6 GHz (top row) as well as at 5 GHz (bottom row) (the sample was not selected on flat radio spectrum!) Compact sources, but 4 out of 5 have steep spectrum (α~-0.6) on this scale Current studies. III. VLBI Imaging of high-z quasars - Frey et al. High-z radio quasars with available SDSS spectroscopy Sample selection: z>4.5; compact on FIRST with 8.8 mJy < S 1.4GHz <28.8 mJy z=4.92 α=-0.60 z=5.01 α=-0.58 z=4.73 α=-0.55 z=4.87 α=-0.58

Main current ground VLBI facilities VLBA (δ≥ -30 o) : 327 MHz - 43 GHz, 512 Mbps GMVA (δ≥ -30 o ): up to 86 GHz LBA (southern hemisphere): up to 22 GHz European VLBI Network (δ ≥ -10 o ): GHz, 1 Gbps e-EVN, more flexible and more frequent than EVN Major support provided to new users by the JIVE staff

Future Space VLBI missions Space Radio Telescope – MHz, 1.6, 4.8, GHz ASTRO-G – Dual Pol. – 8.4, 22, 43 GHz sub-mas to μas resolutions from 327 MHz to 43 GHz

Final Considerations VLBI is the only way to directly image the central regions in AGNs The present performances and flexibility of VLBI and e-EVN make AGN cores and jets and very faint AGN the most targeted sources these days The new space and ground-based high energy observatories have revived the interest in the study of the inner regions in powerful radio galaxies: monitoring of large samples are the current approach

Current radio programs - I. Imaging Monitoring MOJAVE Imaging + monitoring survey ( ~ 200 sources) – GHz TANAMI southern monitoring of blazars (~80 sources) – 8.4 & 22 GHz BU Blazar Group 22 & 43 GHz VLBA imaging monitoring of ~ 20 sources VIPS VLBI Imaging and Polarimetry Survey, GHz, ~1200 sources USNO-RRFID Database of geodetic observations at 2.3/8.4 GHz and 22 GHz DXRBS EVN observations at 5 GHz of ~ 100 sources from the DXRBS sample

Current radio programs - II. Single dish monitoring UMRAO UMich Radio Observatory, full polarization long term monitoring at 4.8, 8.4, 15 GHz of ~ 50 bright sources Ratan monitoring survey of ~ 700 bright sources Metsahovi long term monitoring (~ & 37 GHz OVRO daily monitoring of ~ GHz FGamma Eb (11cm to mm)/IRAM (1,2,3 mm) simultaneous monitoring Medicina and Noto Monthly monitoring of ~ 30 sources at 5, 8.4 and 22 GHz