Direct imaging of AGN jets and black hole vicinity Tiziana Venturi [email protected] Active...
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Transcript of Direct imaging of AGN jets and black hole vicinity Tiziana Venturi [email protected] Active...
Direct imaging of AGN jets and black hole vicinity
Tiziana Venturi
Active Galactic Nuclei 9 Ferrara, 27.05.2010
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 pcz=0.1 -> 1 mas = 1.8 pcz=2 -> 1 mas = 8 pc
Unified view of Radio Loud AGNLow 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 BL BL Lac – Red BL 3C454.3 - FSRQ
Cygn A - FRIIM87 - 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. 2001 & 2003
Expanding cloud of relativistic electrons initially thick at some frequencies and viewed very close to the line of sight
PKS 1510-089HPRQ; z=0.36βapp= 23.76c
2200+420BLLac; z=0.0686βapp= 10.57c
1995 - 2010 1995 - 2010 1995 - 2010
3C454.3HPRQ; z=0.859βapp= 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
βapp = 20.57c
Radio galaxy, z=0.033
βapp = 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 > -20o, S2cm > 1.5 Jy at any epoch between 1994 and 2004)
- Monitoring carried out with the VLBA at 2 cm starting from 1994
- 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 (βapp,L) for sources with γ=32 and
L=1025 W/Hz
VLBA observational limit set at S=0.5 Jy and μ=4 mas/yr
Radio galaxies BL Lacs Quasars
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 1510-089 (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 decreasingNo proper motion along the jetNo birth of new components so farFrom 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 2010eVLBI 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 vapp~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 < S1.4GHz <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≥ -30o) : 327 MHz - 43 GHz, 512 Mbps www.nrao.edu
GMVA (δ≥ -30o ): up to 86 GHz
LBA (southern hemisphere): up to 22 GHz
European VLBI Network (δ ≥ -10o): 1.4- 22 GHz, 1 Gbps
e-EVN, more flexible and more frequent than EVN
www.evlbi.org
Major support provided to new users by the JIVE staff
Future Space VLBI missions
Space Radio Telescope – 2011 327 MHz, 1.6, 4.8, 15-22 GHz www.asc.rssi.ru/radioastron/news/news.html
ASTRO-G – 2014 www.vsop.iasa.ac.jp/vsop2
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) – VLBA @15 GHz
TANAMI
southern monitoring of blazars (~80 sources) – LBA @ 8.4 & 22 GHz
BU Blazar Group
22 & 43 GHz VLBA imaging monitoring of ~ 20 sources
VIPS
VLBI Imaging and Polarimetry Survey, VLBA@5 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 (~ 100 sources) @ 22 & 37 GHz
OVRO
daily monitoring of ~ 1000 sources @ 15 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