Transcript Document

Direct imaging of AGN jets and black
hole vicinity
Tiziana Venturi
[email protected]
Active Galactic Nuclei 9
Ferrara, 27.05.2010
Radio VLBI as the most direct way to look into the inner
regions of AGNs
z=0.01 -> 1 mas = 0.2 pc
z=0.1 -> 1 mas = 1.8 pc
z=2 -> 1 mas = 8 pc
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
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
Mkn 421
3C454.3
BL Lac
Markarian 421 – Blue BL
M87 - FRI
BL Lac – Red BL
M87
3C454.3 - FSRQ
Cygnus A
Images from MOJAVE at 15GHz
Cygn A - FRII
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
Sample of nearby
BLLacs
(Giovannini et al. 2001)
(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:
Observer
-
Strong flux density variability
-
Morphological changes implying
superluminal speeds
-
Instabilities in the radio jet
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
Structural variability and superluminal motion
Favourable viewing angle and high intrinsic speed of the radio emitting
plasma, lead to superluminal proper motion
1995 - 2010
PKS 1510-089
HPRQ; z=0.36
βapp= 23.76c
1995 - 2010
2200+420
BLLac; z=0.0686
βapp= 10.57c
1995 - 2010
3C454.3
HPRQ; z=0.859
βapp= 14.19c
Polarization and total intensity movies from MOJAVE
3C279
VLBA
43GHz
HPRQ, z=0.536
Radio galaxy, z=0.033
βapp = 20.57c
βapp = 5.43
Current studies. I. Statistics from the MOJAVE survey
The sample & the project
Ideal band: high angular
resolution,
very good
- Nearly 300 compact AGN in the Northern Sky,
135 of which
formimage
a
and better
o, S
complete flux density limited sample (δ > -20sensitivity
2cm > 1.5 Jy at any
reliability compared to BU
epoch between 1994 and 2004)
monitoring
- 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
Analysis carried out for BL Lacs, FSRQ and radio galaxies
separately (Lister et al. 2009)
Peak at
~ 10c
Fastest component moving at
50.6c and interpreted as the
upper end of the AGN jet Lorentz
factor distribution
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
Current studies. II. Simultaneous radio/γ-ray monitoring with
VLBI imaging
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)
γ-ray
radio
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
Flares in the optical and γ-ray band
Slow monotonic flux density
increase at radio wavelengths
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
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
vapp~7c
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
z=5.01
α=-0.60
α=-0.58
z=4.73
z=4.87
α=-0.55
α=-0.58
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
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