Tiziana Venturi tventuriirainafit Active Galactic Nuclei 9 Ferrara 27052010 Radio VLBI as the most direct way to ID: 378921
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Slide1
Direct imaging of AGN jets and black hole vicinity
Tiziana Venturi
tventuri@ira.inaf.it
Active Galactic Nuclei 9 Ferrara, 27.05.2010Slide2
Radio VLBI
as the
most direct
way to look into
the inner regions of
AGNsKnowledge 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 Slide3
Unified view of Radio Loud AGN
Low power
FR I and
BL Lacs
High power
FR II and FSRQUnification 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 Slide4
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 - FRIImages from MOJAVE at 15GHzMkn 421BL Lac3C454.3M87Cygnus ASlide5
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 factorsSlide6
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 sightSlide7
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 variabilityMorphological changes implying superluminal speedsInstabilities in the radio jet
ObserverSlide8
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
Slide9
PKS 1510-089
HPRQ; z=0.36
β
app= 23.76c
2200+420BLLac; z=0.0686β
app= 10.57c
1995 - 20101995 - 20101995 - 20103C454.3HPRQ; z=0.859βapp= 14.19cStructural variability and superluminal motionFavourable viewing angle and high intrinsic speed of the radio emitting plasma, lead to superluminal proper motionPolarization and total intensity movies from MOJAVESlide10
3C279 VLBA 43GHz
HPRQ, z=0.536
β
app
= 20.57c
Radio galaxy, z=0.033
βapp = 5.43Slide11
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 sources526 separate features in 127 jets (no speed measurements for 8 sources) database consisting of 2424 imagesIdeal band: high angular resolution, very good image sensitivity and better reliability compared to BU monitoringSlide12
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
~
10cApparent velocity vs redshift: the distribution is not the result of observational limitationsSlide13
Locus of (
β
app
,L) for sources with γ=32 and L=1025
W/HzVLBA observational limit set at S=0.5 Jy and
μ
=4 mas/yrRadio galaxiesBL LacsQuasarsSlide14
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 radioγ-ray γ-ray flareSuperluminal ejection Slide15
PKS 1510-089
(Marscher et al. 2010)VLBA 43 GHz monitoring & Fermi LAT and AGILE observations
Optical
and γ-ray
flares
in good coincidenceRotation of the optical polarization vector2 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 zoneSlide16
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 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~20Flares in the optical and γ-ray bandSlow monotonic flux density increase at radio wavelengths Slide17
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 energiesSlide18
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~7cSlide19
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 scaleCurrent studies. III. VLBI Imaging of high-z quasars - Frey et al.High-z radio quasars with available SDSS spectroscopySample selection: z>4.5; compact on FIRST with 8.8 mJy < S1.4GHz <28.8 mJyz=4.92α=-0.60z=5.01α=-0.58z=4.73α=-0.55z=4.87α=-0.58Slide20
Main
current
ground VLBI facilities
VLBA (δ≥ -30
o)
: 327 MHz - 43 GHz, 512 Mbps www.nrao.eduGMVA (δ≥ -30o ): up to 86 GHzLBA (southern hemisphere): up to 22 GHz European VLBI Network (δ ≥ -10o): 1.4- 22 GHz, 1 Gbpse-EVN, more flexible and more frequent than EVNwww.evlbi.orgMajor support provided to new users by the JIVE staffSlide21
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 GHzSlide22
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 approachSlide23
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 sourcesVIPSVLBI Imaging and Polarimetry Survey, VLBA@5 GHz, ~1200 sourcesUSNO-RRFIDDatabase of geodetic observations at 2.3/8.4 GHz and 22 GHzDXRBSEVN observations at 5 GHz of ~ 100 sources from the DXRBS sample Slide24
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 sourcesMetsahovi
long term monitoring (
~ 100 sources) @ 22 & 37 GHz OVRO daily monitoring of ~ 1000 sources @ 15 GHzFGammaEb (11cm to mm)/IRAM (1,2,3 mm) simultaneous monitoringMedicina and Noto Monthly monitoring of ~ 30 sources at 5, 8.4 and 22 GHz