Global Millimeter VLBI: Where do we
stand ?
T.P.Krichbaum
Max-Planck-Institut für Radioastronomie
Bonn, Germany
tkrichbaum@mpifr.de
people involved in Global Millimeter VLBI (GMVA):
MPIfR: W. Alef, U. Bach, A. Bertarini, T. Krichbaum, R. Porcas, J.A. Zensus, et al.
IRAM:
M. Bremer, A. Grosz, S. Sanchez, K. Schuster, et al.
OSO:
J. Conway, M. Lindqvist, I. Marti-Vidal, et al.
OAN:
P. Colomer, P. de Vicente, et al.
INAF:
S. Buttaccio, G. Tuccari, et al.
NRAO: W. Brisken, C. Chandler, M. Claussen, V. Dhawan, C. Walker, et al.
KVN:
B.W. Sohn, T. Jung, S.S. Lee, et al.
plus: A. Marscher's BU group
1mm VLBI, EHT collaboration (in 2013) :
APEX:
R. Güsten, K. Menten, D. Muders, A. Roy, J. Wagner, et al.
Haystack: S. Doeleman, V. Fish, R. Lu, M. Titus, R. Capallo, et al.
CARMA: G. Bower, R. Plambeck, M. Wright, et al.
since 2015: + BHC Team:
JCMT:
P. Friberg, R. Tilanus, et al.
SMA:
R. Blundell, J. Weintroub, K. Young, et al.
SMTO:
R. Freund, D. Marrone, P. Strittmatter, L. Ziurys et al.
C. Brinkerink, H. Falcke,
R. Tilanus, et al.
The Origin of Jets: Understanding BH – Disk – Jet coupling
Image Credit: Astronomy/Roen Kelly
- VLBI at mm- l overcomes opacity barrier
- mm-VLBI and space-VLBI probe jet origin
How are jets made – a sketch of present knowledge
image: Rani@MPIfR, Marscher@BU
this region can be probed by mm-VLBI and by variability studies (at high energies)
with mm-VLBI we can measure:
• jet brightness temperature as function of BH separation for r < 1000 RS
• opacity and radial dependence of t=1 surface (core shift)
• polarization / magnetic field vs. r
• BH mass and spin, respectively set observational limits to these
Blandford – Payne mechanism:
BP versus BZ mechanism
centrifugal acceleration by
magnetized accretion disk wind
Blandford – Znajek mechanism:
measure
electromagnetic extraction of
rotational energy from Kerr BH
Jet speed f(r,z)
Jet width f(z)
TB f(z)
→
Shape of Nozzle
BP:
Magnetic Field
BH Spin
BZ:
Jet
etc.
Light cylinder
need to reach
scale of
a few RG
B-field
A 3mm VLBI survey of 127 AGN:
Brightness temperature decreasing with
increasing frequency ?
Lee et al. 2008, 2015
86 GHz data
Figure adopted from
A. Marscher (1995)
M87
Brightness temperature increasing along
jet; evidence for intrinsic acceleration ?
mm-VLBI imaging of
AGN can discriminate
between fundamental
models of jet formation
VLBI with ALMA
Lee et al. 2008 (AJ)
3C279 @ 230 GHz:
86 GHz (GMVA)
APEX
beam: 37 x 15 mas
compactness:
EHT @ 230 GHz
10-15 % !!
SNR ~ 10-20
SMA-SMTO
Apex-SMTO
Apex-SMA
VLB-Arrays observing at mm-wavelength
• 43 GHz: VLBA(10), EVN (5), KaVa (7), HSA (12+)
• 86 GHz: GMVA(15), VLBA(8), HSA(10) KVN(3)
• 129 GHz: KVN(3), PV, PdB, SMTO, ....
no joined activity yet
• 230 GHz: PV, APEX, SMTO, SMA/JCMT, LMT,
planned: ALMA, SPT, NOEMA, GLT, ....
future:
• 350 GHz: PV, PdB, SMTO, SMA/JCMT, APEX, ALMA, SPT, KP12m
The Global Millimeter VLBI Array (GMVA)
Imaging with ~45 mas resolution at 86 GHz
Baseline Sensitivities
GBT100m
in Europe:
30 – 250 mJy
in US with GBT:
50 – 250 mJy
Yebes (OAN)
best transatlantic:
30 – 100 mJy
Array:
0.5 – 1 mJy / hr
(assume 7s, 100 sec, 2 Gbps)
http://www.mpifr-bonn.mpg.de/div/vlbi/globalmm
• Europe: Effelsberg (100m), Pico Veleta (30m), Plateau de Bure (35m), Onsala (20m),
Metsähovi (14m), Yebes (40m), KVN (3 x 21m), planned: SRT, NOEMA, ...
• America: 8 x VLBA (25m), GBT (100m), planned: LMT, ALMA, ...
Proposal deadlines: February 1st, August 1st
3mm VLBI sensitivity enhanced by inclusion of large
European mm-telescopes:
Effelsberg 100 m (MPIfR)
Plateau de Bure, 6 x 15 m
(IRAM, France)
Yebes 40 m (OAN, Spain)
Pico Veleta 30 m (IRAM, Spain)
Baseline lengths (km):
PV PdB Yb
EB 1700 658 1352
PV
1146 384
PdB
866
fringe spacing: 0.4 – 1.8 mas,
sensitivity > 15 - 50 mJy (7s, 2Gbps)
participating since
2011
Green Bank 100m telescope participates
in GMVA 3mm VLBI observations
1st test observations in Feb. 2013
2 Gbps, 1 RDBE, PFB mode
SEFD ~ 164 K
app. eff ~ 0.26 (for s = 173 mm)
POSSM plot after FRING:
(solint 2min)
RR
LL
Polarized sub-structure in jet of BLLac on 0.1 mas scales
Jan. 15
Feb. 18
43 GHz
86 GHz
VLBA
GMVA
polarized jet emission on scales down to 50 mas
3mm VLBI Array Sensitivities
Array
Stations
VLBA, 2 Gb/s
GMVA, 2 Gb/s
+ Yb
+ LMT + GBT
+ ALMA
VLBA(8)
VLBA+EB+PV+PB+ON+MH
present GMVA+Yebes
present GMVA+Yebes+LMT+GBT
present GMVA+Yebes+LMT+GBT+ALMA
Baseline
Array 12hr Map Comment
[mJy]
[mJy/hr] [SNR]
> 164
> 33
> 27
> 10
> 5
2,33
0,86
0,67
0,30
0,19
1.0e03
2.8e03
3.7e03
8.2e03
12.9e03
no HN, no SC
68 mJy VLBA-IRAM
68 mJy VLBA-Yb
31 mJy VLBA-GBT
5 mJy ALMA-GBT
assuming: 512 MHz bandwidth (2 Gbit/s), t=20 sec, 7sigma fringe detection, 2 bit sampling
• Combining European mm-telescopes with the VLBA improves the angular
resolution by factor ~ 2 and imaging sensitivity by a factor of ~2 - 3.
• The addition of telescopes with large collecting area (GBT, LMT,SRT, ...) will
give another factor of 2 - 3.
• Participation of ALMA leads to mJy sensitivities and will improves the overall
sensitivity by a factor of 5 over present day values.
• Another factor of sqrt(rate/2Gbps) in sensitivity can be obtained via a
further increase of the observing bandwidth.
First Fringes between KVN and GMVA (86 GHz, May 2012)
3 x 21 m, baselines 305 – 478 km
0716+714
KVN – PdBI: SNR ~ 11 on 1 Jy source
PB-KU
256 Mbps
KY-KU
RR
LL
86 GHz VLBI Fringes VLBA to KVN
GMVA Session May 2015 (PFB, now 1 Gbps)
LCP
KVN Yonsei – VLBA Brewster:
B= 7860 km
SNR ~ 22 on 0716+714 (Stot ~ 2 Jy)
tint = 388 sec, 1 Gbps
RCP
S. Koyama+
S. Koyama+ 2015
Dec +20
Dec +50
KVN stations improve uv-coverage and resolution of GMVA
long baselines
with Europe at
start
KVN
KVN
VLBA
Europe
Europe
long baselines with
VLBA at end
VLBA
baseline sensitivities:
KVN – GBT ~
0.07 Jy
KVN – IRAM ~
0.15 Jy
KVN – VLBA ~
0.35 Jy
(7 s, t=10 sec, 1024 Mbps)
OJ 287: Spectral decomposition of core using GMVA
VLBA 15 GHz
VLBA 43 GHz
GMVA 86 GHz
G
M
V
A
beam: 0.22 x 0.043 mas
Rcore < 0.04 mas
The core is South!
(180 Rs9)
TB ~ 2.4 E11 K
modelfit: 0.21 x 0.043 mas beam
total spectrum from FGAMMA monitoring program
VLBI component spectra from VLBI at 15 + 43 + 86 GHz, need to add 230 GHz
The next step towards truly global 1.3 mm VLBI array (EHT)
Status March 2013 with APEX added
GLT
PdBure
CARMA
Pico Veleta
SMTO
LMT
JCMT+SMA
APEX/ALMA
existing
planned
SPT
fringes established
M87 at 86 and 230 GHz
May 2009
GMVA @ 86 GHz
(11 stations)
beam (290 x 50) mas = (37 x 6) RS
EHT @ 230 GHz:
Mar. 2013
(4 stations)
Modelfit + Clean Map
uvtaper 0.3@6Gl
Core jet structure traced down to ~25 mas
scale
small core size indicates BH spin a > 0
beam 59 x 24 mas = (7.4 x 3.9 RS)
M87's core size is smaller than previously thought
VLBI core size at 86 GHz, new
VLBI core size at 230 GHz, new
new data point
core size:
23 mas or
2.9 Rs
I
This is smaller
than the
photon ring for
an a=1 BH !
APEX baselines are more N-S oriented, than the E-W orientation of the US-array:
the above numbers may measure the N-S jet width or sheath rather than the core !
Competing Jet Models
synchrotron self-absorbed conical jet plus
relativistic shocks (Blandford-Königl jet)
2 R0 ≥ 10 RS (a=0)
stratified (MHD) jet with moving hot
spots/shocks or filamentary patterns
Figure from Hada et al. 2011, Nat.
last stable orbit radius: 1 → 6 Rs for BH spin a = 1 → 0
still unclear of what is seen at 1mm, need complementary imaging with GMVA
230 GHz structure may trace edge-brightening in 3C279
Krichbaum+2013, Wagner+ 2015
EHT 230 GHz
May 7, 2012
GMVA 86 GHz
0.6 pc
May 17, 2012
core < ~1300 RS
beam: 274 x 73 mas
beam: 37 x 15 mas
base of jet is transversely resolved and has a width of ~1 pc (~104 RS)
size of individual components (emission regions) < 0.1 pc (1000 RS)
Cygnus A: stacked VLBI image at 86 GHz
(3 epochs, 2009 – 2010, 512 Mbps)
1 mas = 1.1pc
0.1 mas ↔ 0.11 pc ↔ 440 Rs9
• jet transversely resolved on pc-scales
core size: ≤ 46 mas or 200 Rs9
• evidence for conical jet opening on jet side (at r < 1pc)
• c-jet opening angle more narrow by factor 2
Boccardi et al. 2015
Ridgeline at 86 GHz, Oct. 2009
(work in progress)
Cyg A
core
ridgeline separation : ~ 0.1 mas (~ 400 Rs9) for jet & cjet
evidence for conical opening both in jet and c-jet
Boccardi et al., in prep
Astrometry at mm-wavelength
Because of phase self-calibration in VLBI, the absolute position
information is lost.
Due to rapid atmospheric phase-variations classical phase-referencing
VLBI via position switch is limited to close source pairs.
With the phase-transfer method applied to 2 or more frequencies
observed simultaneously, VLBI maps at different frequencies could be
aligned. The positional accuracy of the alignment will be of order of a
fraction of the beam (< 50 micro-arcseconds at 86 GHz).
An accurate image alignement is required for:
• spectral index measurements of cores and jets
• source kinematics at different frequencies (stratification)
• measurement of opacity shifts in RA and DEC
• determination of rotation measure
Phase-referencing at 86 GHz is possible for close source pairs
Phase vs. time
1308+326, 709 mJy
hybrid map of
calibrator
1308+328, 85 mJy
phase-reference
map of target
distance: 14'.3
cycle: 10 – 20 s
rate: 256 Mbps
VLBA supports rapid enough switching
Porcas & Rioja, 2002
VLBI frequency agility between 22-129 GHz
(preliminary)
Station
Country D
BW
Effelsberg
Pico Veleta
P. de Bure
Yebes
Onsala
Noto
Metsahovi
Germany
Spain
France
Spain
Sweden
Italy
Finland
100m
30m
6x15m
40m
20m
32m
14m
GBT
VLBA
USA
USA
KVN
Vera
Alma
13mm
7mm
3mm
2 Gbps
16 Gbps
1 Gbps
2 Gbps
2 Gbps
2 Gbps
2 Gbps
y
n
n
y
y
y
y
y
n
n
y
y
y
y
y
y
y
y
y
n
y
n
y
y
n
?
n
?
30 min- 1hr
simultaneous
simultaneous?
minutes
no
no
no
100m
10x25m
2 Gbps
2 Gbps
y
y
y
y
y
y
n
n
no
seconds
Korea
Japan
3x21m
4x20m
1 Gbps
1 Gbps
y
y
y
y
y
n
y
n
simultaneous
no
Chile
66x12m
32 Gbps
n
planned
y
y
sub-arraying
2mm Freq. agile
note: consider hybrid phase transfer: some stations observe only at one frequency
need to develop strategies how to tie in phases for these stations
Summary and Outlook
• the Origin of Jets in AGN can be studied at 7mm, 3mm and now also at 1mm
• 3mm and 7mm VLBI is almost standard (< 2 Gbps), VLBI @ 1mm is nonstandard (16 Gbps in 2015, aim at 32 Gbps)
• participation of large collecting area dishes now provide much higher sensitivity
(IRAM, GBT, Effelsberg, Yebes, soon: LMT, ALMA, ...)
• VLBA provides important uv-coverage and frequency agility (43/86 GHz)
• calibration limitations due to weather are over-come with an increased
antenna number, which facilitates the use of closure amplitudes (N > 12)
• advanced methods in global-fringe fitting could be implemented to further
optimize the array sensitivity (incoherent averaging, etc.)
• a further increase of the observing bandwidth beyond 2 Gbps at 3mm/7mm
is highly desirable (ALMA: 32 Gbps)
• dual/multi frequency phase transfer capabilities are not yet in place
• a denser time sampling is necessary to better trace rapidly evolving sources
• 1.3 mm-VLBI (EHT) is limited and requires complementary global 7 & 3 mm
VLBI (better uv-coverage, sensitivity, beam size within a factor of 2)