1. Global Millimeter VLBI: Where do we stand ?
T.P.Krichbaum
Max-Planck-Institut für Radioastronomie
Bonn, Germany
This is the final version

2. 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.
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.
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.
plus: A. Marscher's BU group
since 2015: + BHC Team:
C. Brinkerink, H. Falcke, R. Tilanus, et al.

3. 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

4. How are jets made – a sketch of present knowledge
image:
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

5. BP: BZ: BP versus BZ mechanism Blandford – Payne mechanism:
centrifugal acceleration by magnetized accretion disk wind
BP versus BZ mechanism
Blandford – Znajek mechanism:
electromagnetic extraction of rotational energy from Kerr BH
measure
Jet speed f(r,z)
Jet width f(z)
TB f(z) →
Shape of Nozzle
Magnetic Field
BH Spin
etc.
need to reach
scale of
a few RG
Light cylinder
BP:
Jet
B-field
BZ:

6. A 3mm VLBI survey of 127 AGN:
Brightness temperature decreasing with increasing frequency ?
Lee et al. 2008, 2015
86 GHz data
M87
Figure adopted from
A. Marscher (1995)
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 (AJ)

7. 3C279 @ 230 GHz: compactness: 10-15 % !! 86 GHz (GMVA) APEX
230 GHz
SMA-SMTO
Apex-SMTO
Apex-SMA
SNR ~ 10-20
beam: 37 x 15 mas
APEX
compactness:
10-15 % !!
3c279, z=0.5362, 1 mas=6.31pc, 0.1 mas= 0.63pc=6476 Rs9, 0.15 muas= 0.095pc=973 rs (1pc =10280 Rs9)

8. 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

9. The Global Millimeter VLBI Array (GMVA)
Imaging with ~45 mas resolution at 86 GHz
Baseline Sensitivities
in Europe:
30 – 250 mJy
in US with GBT:
50 – 250 mJy
best transatlantic:
30 – 100 mJy
Array:
0.5 – 1 mJy / hr
(assume 7s, 100 sec, 2 Gbps)
GBT100m
Yebes (OAN)
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

10. 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):
participating since 2011
fringe spacing: 0.4 – 1.8 mas,
sensitivity > mJy (7s, 2Gbps)

11. POSSM plot after FRING:
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

12. Polarized sub-structure in jet of BLLac on 0.1 mas scales
43 GHz
VLBA
86 GHz
GMVA
Jan. 15
Feb. 18
polarized jet emission on scales down to 50 mas

13. 3mm VLBI Array Sensitivities
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
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.

14. First Fringes between KVN and GMVA (86 GHz, May 2012)
3 x 21 m, baselines 305 – 478 km
KVN – PdBI: SNR ~ 11 on 1 Jy source
PB-KU
256 Mbps
KY-KU
RR LL

15. 86 GHz VLBI Fringes VLBA to KVN
GMVA Session May 2015 (PFB, now 1 Gbps)
LCP
90 mas
RCP
KVN Yonsei – VLBA Brewster:
B= 7860 km
SNR ~ 22 on (Stot ~ 2 Jy)
tint = 388 sec, 1 Gbps

16. S. Koyama+
S. Koyama+ 2015

17. KVN stations improve uv-coverage and resolution of GMVA
Dec +20
Dec +50
KVN stations improve uv-coverage and resolution of GMVA
KVN
VLBA
Europe
long baselines with Europe at start
long baselines with VLBA at end
baseline sensitivities:
KVN – GBT ~ 0.07 Jy
KVN – IRAM ~ 0.15 Jy
KVN – VLBA ~ 0.35 Jy
(7 s, t=10 sec, 1024 Mbps)

18. OJ 287: Spectral decomposition of core using GMVA
VLBA 43 GHz
GMVA 86 GHz
VLBA 15 GHz
beam: 0.22 x mas
Rcore < 0.04 mas
(180 Rs9)
TB ~ 2.4 E11 K
The core is South!
modelfit: 0.21 x mas beam
total spectrum from FGAMMA monitoring program
VLBI component spectra from VLBI at GHz, need to add 230 GHz

19. The next step towards truly global 1.3 mm VLBI array (EHT)
Status March 2013 with APEX added
APEX/ALMA
LMT
SMTO
CARMA
JCMT+SMA
Pico Veleta
PdBure
SPT
GLT
existing
planned
fringes established

20. M87 at 86 and 230 GHz GMVA @ 86 GHz (11 stations) EHT @ 230 GHz:
beam (290 x 50) mas = (37 x 6) RS
May 2009
86 GHz
(11 stations)
230 GHz:
(4 stations)
Modelfit + Clean Map
uvtaper
Mar. 2013
1mas = 126 Rs
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)

21. M87's core size is smaller than previously thought
VLBI core size at 86 GHz, new
VLBI core size at 230 GHz, new I
new data point
core size:
23 mas or
2.9 Rs
This is smaller than the photon ring for an a=1 BH !
1 mas = 126 Rs, photon ring size for max. spinning 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 !

22. last stable orbit radius: 1 → 6 Rs for BH spin a = 1 → 0
Competing Jet Models
synchrotron self-absorbed conical jet plus relativistic shocks (Blandford-Königl jet)
stratified (MHD) jet with moving hot spots/shocks or filamentary patterns
2 R0 ≥ 10 RS (a=0)
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

23. 230 GHz structure may trace edge-brightening in 3C279
Krichbaum+2013, Wagner+ 2015
GMVA 86 GHz
beam: 274 x 73 mas
May 17, 2012
EHT 230 GHz
beam: 37 x 15 mas
May 7, 2012
0.6 pc
core < ~1300 RS
3c279, z=0.5362, 1 mas=6.31pc, 0.1 mas= 0.63pc=6476 Rs9, 1pc=10289 Rs9
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)

24. 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
core size: ≤ 46 mas or 200 Rs9
jet transversely resolved on pc-scales
evidence for conical jet opening on jet side (at r < 1pc)
c-jet opening angle more narrow by factor 2
Boccardi et al. 2015

25. 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

26. 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

27. Phase-referencing at 86 GHz is possible for close source pairs
Phase vs. time
, 709 mJy
hybrid map of calibrator
, 85 mJy
phase-reference map of target
distance: 14'.3
cycle: 10 – 20 s
rate: 256 Mbps
Porcas & Rioja, 2002
VLBA supports rapid enough switching

28. VLBI frequency agility between 22-129 GHz
(preliminary)
note: consider hybrid phase transfer: some stations observe only at one frequency
need to develop strategies how to tie in phases for these stations

29. 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), 1mm is non- standard (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)

30. End